Ecological and Morphological Studies of the Genus

Oncorhynchus (Salmonidae) with particular
Consideration on Phylogeny.
Toyohiko HIKITA

Contents

I . INTRODUCTION

II . ACKNOWLEDGEMENTS
III. MATERIAL AND METHODS
N . DESCRIPTIONS
1. General Remarks
1. External and ecological features of the Pacific salmon.
2. Osteological structures of the chum salmon (0. keta).
A) Axial skeleton
Skull, Hyoid arch, Branchial arch and Vertebral column.
B) Appendicular skeleton .. Vertical fins, paired fins and their girdles.
3. Morphological characters for species discrimination.
( 1 ) Coloration and some spot-patterns(2 ) Lateral line scale( 3 ) Number of fin rays
( 4 ) Number and form of gill-rakers( 5 ) Number of branchiostegal rays
( 6 ) Number of vertebral column( 7 ) Transverse fold of the intestine and its number( 8 ) Form and structure of scales( 9 ) Number of pyloric caeca(10) Form and number of pseudobranchiae(11) Form of appendicular scale(12) Number of the chromosomes
Part 2. Difference of external characters between salmon fingerling and adult stages.
Part 3. Observations of the Pacific salmon, including their distribution.
1. Oncorhynchus heta (Walbaum)
2. Oncorhynchus gorbuscha (Wal baum)
3. Oncorhynchus rnasou (Brevoort)
4. Oncorhynchus tschawytscha (Wal baum)
5. Oncorhynchus nerka (Walbaum)
6. Oncorhynchus kisutch (Walabum)Part-

7. Oncorhynchus rhodurus Jordan and McGregor
Part

8. Oncorhynchus hawarnurue Jordan and McGregor
4. Interspecific relationships of the Pacific salmon with some phylogenetic considerations.

V . SUMMARY

m. REFERENCES
EXPLANATlON O F PLATESContribution No. 170, Hokkaido Salmon Hatchery.

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

I , INTRODUCTION
The Pacific salmon are one of the important resources as commercial or game fish in
Japan as well as in Canada, North America and eastern Siberia. Of salmon, the following
species keta, gorbuscha and masou, are very common in waters around Japan, particularly
abundant in northern areas, and are caught by fishermen in coasts and streams of Hokkaido.

The Pacific salmon have belonged to the genus Oncorhynchus which means ‘‘hooked snout,”
and are distinguished from the Atlantic salmon, Salmo salar which corresponds to “salmon”
in Latin, mainly based on the fact that the latter may spawn more than once in their life
cycle, while Pacific salmon almost all die after spawning. T h e salmon, which have generally
been regarded as cold water inhabitants, are known to naturally spawn only in some definite
regions in the upper reaches of rivers or streams. Therefore, if the spawning environments
would be damaged by certain causes, they would be unable to spawn there, and in consequence there would follow a gradual decrease in the population of the succeeding generation.
Recently, in Hokkaido there have been an increasing number of fatal obstacles such as river
blockades by the dams of electrical plants and by irrigation works, or water-exhaustion due
to deforestation which hinders ascending spawners, and also water pollution flowing intodrainages, the Ivastes from various factories and dwellings in cities, which all combined
are injurious to descending migrants. For the conservation and maintenance of future salmon
population, it is, therefore, necessary to legally enforce the fisheries administration against
various harriers to stream reservations on the one hand, and on the other hand to powerfully push forward to further the artificial propagation from the ecological point of view
Reference to the literature indicates that a number of essential studies on Pacific salmon
mainly on their morphology and ecology have long been conducted by many zoologists andichthyologists, and that there have been published a considerable amount of work concerning
their life histories, distribution, propagation and managements. These previous investigations
are, however, mostly fragmentary and incomplete, and therefore one’s knowledge on themorphological and ecological aspects of Pacific salmon has remained quite in sufficient.
T h e basic data for understanding the taxonomy and phylogeny of salmon are incomplete
at present.

In general, the Salmonidae are the fishes in which the classification has been

carried out with many difficulties.

There are many controversies in the classification of

the Salmonidae because of incomplete status of knowledge on their morphology, ecology
and other taxonomic character.

Morphologically the salmonid fishes are rather variablein many respects, and on this basis they are highly difficult to discriminate or identify the
specific, or sometimes generic relation. Recently, the salmon population is showing a generaltendency to decrease in number, due to a number of environmental obstacles. In addition,
the production of hybrid fishes in the field population and the artificial condition seems toenhance the difficulty of taxonomy of salmon because of considerable confusions of theirexternal features.

Farther, there is some difficulty in collection of favourable material,

particularly in securing the material in good season available for taxonomical study-. Inview of the above status, therefore, the need fore more exact knowledge of morphology

Ecological and Morphological Studies of the Genus Oncorhynchus

and ecology in various species of the Salmonidae has been increasing for the sake of theestablishment of the scientific current taxonomy of this economically important group offishes. In order to make some contributions to this field, the present author has undertaken
a comparative morphological and ecological, investigation in the Salmonidae, with particularregard to the phylogenetic significance of morphological and ecological characters on one
hand, and on the other hand with hope to formulate any morphological relationship into
systematics. In observation, special attention has been paid towards the morphological andecological differences through a close comparison between related species, in order to understand the mechanism and processes of species formation and to obtain any critical information on the phylogenetic relationship of salmonid fishes.
The results of the present observations will be described in four parts in the following
pages. In part 1 are given general remarks on external morphology and ecology of thepacific salmon, some osteological structures of the chum salmon, and morphological characters for species discrimination, such as coloration, lateral line scale, number of fin rays,
vertebral column, chromosomal conditions, and so on. Part 2 deals with the difference of
external characters between fingerling and adult salmon.

?

art 3 is devoted for generalinvestigations regarding some morphological and ecological features of the Pacific salmon
including their distribution. In part 4, the interspecific relationships of the Pacific salmon
are to he discussed with special regard to their phylogeny

1 . ACKNOWLEDGEMENTS
Before going further the writer’s cordinal thanks are due to Emeritus Professor Dr.
Tohru Uchida, Hokkaido University, and Former Instructor Mr. Toyoji Hikita, the FisheriesInstitute at the same University, for their valuable advices and important suggestions given
with course of this work. The writer also wishes to express his sincere gratitude to Professor Dr. Sajiro Makino, Faculty of Science, Hokkaido University, for his continuous guidance and encouragement, and for his kindness in critical reading and improving of thismanuscript. Sincere thank are also due to Dr. Atsuhiko Ichikawa, Faculty of Science,
Hokkaido University, for his powerful encouragement, and to Dr. C. C. Lindsey, the Institute of Fisheries, the University of British Columbia, Mr. Milo E. RIoore, Former Directorof the Washington State Department of Fisheries, and to Mrs. T. B. Egorova, Chief ofthe Kuril T-ake Salmon Counting Observatory, under the Pacific Fisheries-Oceanographic
Institution, Kamchatka, for their kind help and facilities in examining specimens preserved.
Deep gratitude is to be recorded for many other persons who placed materials to theauthor’s disposal, and provided with generous advice and assistance ; Dr. Tokiharu Abe,
Tokai Reg. Fish. Res. Lab., Mr. Tatsuro Kuho, Mr. Kiyu Kobayashi and Mr. Jun Kosaka,of the Fisheries Department, Hokkaido University, Mr. Tsutoinu Hisa, Nikko Trout Hatchery, Fisheries Agency, Mr. Sadaji Arai, Former Director, Drs. Seizo Sano and Tetsuo
Kobayashi, Messers. Hiroshi Eguchi, Kazuhiko Nishino, Toshinobu Tokui, Ei-ichi Sakano,
Shinichi Abe, Twao Miura, Takashi Kurohagi, Minoru Osanai, Ariaki Nagasawa, Shoichi
Ohkubo, Yoshiji Ozaki, Ryuji Fumoto, Yokichi Sasaki, Mrs. Mitsue Sato, of the hatchry,
3

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

5staff members of the Shiga Prefectural Fisheries Station, and Messers. Seiro Kimura andOsamu Tabeta, Postgraduate Research students of the Fisheries Department, Kyushu
University.

5 . MATERIAL AND METHODS
T h e vast majority of materials examined in the present study was obtained from thefollowing localities, including two foreign countries. they werc collected during a period
from 1950 to present date. Collecting streams and lakes are as follows:
Iwaobetsu, Tokoro, Horonai, Rausu, Shynkarikotan, Kunbetsu, Nishibetsu, Shibetsu,
Kushiro, Tokachi, Memu, Ishikari, Teshio, Yobetsu, Shizunai, Oboro, Yufutsu, Yurappu,
Moheji, Shiriuchi, Shubuto, Toshibetsu, Makomanai, Atsubetsu, Kamihara and Muromi(northern Kyushu), Lakes ; Shikotsu, Akan, Chimikeppu, Kutara, Toya, Towada and Tazawa(Akita Prefecture), Biwa (Shiga Prefecture), Chyuzenji (Tochigi Prefecture), Takadomari
Reserviour, Uryu Reserviour ; Brigade Bay and Swelter Creek (Canada), Lake Kuril(Russia), North Pacific Ocean and Bering Sea.
All specimens herein dealt with were preserved in 10 per cent formalin, except for apart of fresh materials which were observed in the field and used for a osteological study.

The meristic measurements and orders of various parts of the body were made as
below :
Total length-From

the tip of snout to the posterior end of the developed caudal fin ray.

The caudal fin tip is often fray or worn off, especially in spawning adults.
Fork length-From

the tip of snout to the fork of the caudal fin.

Standard length-Fromsnout tip to the last scale on the lateral line of the caudal fin base.

This length often termed by several authors concerned in ecological investigations
as “Body proper length”, which seems more accurate than total length.
Head length-From
Depth-Vertical

tip of snout to the opercular margin.

distance of body measured at deepest part, excepting just before dorsal

fin.
Snout length-From

tip of snout to the anterior rim of eye.

Eye-Antro-posterior

diameter of the eye ball measured horizontally.

hlaxillary - From anterior tip of maxillary to its distal end.
Postorbital part of headTFrom the posterior margin of the orbit to the extreme end of theopercular flap.
Interorbital width-The
shortest distance between left ,and right orbit on head.
Depth of the caudal peduncle-The least vertical depth of the caudal peduncle: the lengthof the same is the distance from the base of last anal ray to the lower origin of
the caudal fin.
Hight of fin-From base of the longest ray to its apex: the length of the same fin is measured the distance from the origin of fin ray to base of the last ray, excepting
caudal fin.
All of the fin rays are counted, and when the last fin rays of dorsal and anal are
divided into two at terminal part they were counted as one.
4

Ecological and Morphological Studies of the Genus Oncorhynchusf

Pectoral and ventral fi-umbers-All the rays are enumerated, including a stout rudiment
ray which clo ely adhere to the second one.

Lateral line scale-Counted

as scale in lateral line from the first scale bearing a tubularpore above operculum to last one on the caudal base, running longitudinally the
middle part of body side.
Gill-rakers-All

the rakers are counted.

Vertebral counts-The

last vertebra combined with an upper hypural, thence number ofvertebrae enumerated from first vertebra to the hypural on the vertebral column,
the vertebra bearing a well developed haemal spine is treated as the first caudal
vertebra.
Position of fin-Measured

a straight length from the tip of snout to the commence of dorsal,

pectoral, anal and ventral fins.
All the materials for the osteological study were used mainly in fresh, and they werelightly boiled to remove the flesh from the bones, some of them after being held in theformalin for a day.
T h e measuring as shown above is mostly made by a straight line along the length offish placed on a rular board, and others by means of needle-like divider, and read on theruler.

IV. DESCRIPTIONSPart 1. General Remarks
1. External and ecological features of the pacific salmon.
There are some features common to all salmonid fishes, including the pacific salmon.
First of all the general form is moderately elongate or oblong and more or less compressed,
covered with small cycloid scale. It is a typical form suited fur swimming in the water so
as to give the least resistance in movement.

The anterior end of body is pointed or conical.

and its profile becomes gradually high to dorsal fin. T h e ventral outline of body islittle more curved than the dorsal so as to balance the heavy muscle region.

The body

behind dorsal fin is tapering to the caudal, the deepest part of the body being generally
in front of the middle, between the snout and caudal peduncle.

The dorsal fin is locatednearly in the middle portion of body on the back, while the ventral fin is situated on the
opposite side of the dorsal fin.

A small fleshy adipose fin without ray is situated above

posterior part of anal, nearer to the caudal than the dorsal fin. On the adipose fin of themale is commonly larger than that of the female. Head is moderate in form and naked.

But the general form of the body is usually more or less modified in different season:
when spawning season approaches the salmon undergo drastic change in color and body
proportion, particularly in head portion.

The coloration of sea migrants is above bluish,

below uniformly bright silvery white. On the ecological aspects the species of the pacificsalmon are widely distributed in temperate and cold waters, specially more abundant northwards, in the northern hemisphere. Although all species of the pacific salmon have different anadromies, they are naturally of two types, anadromous and land-locked form.
5

Scientific Reports of the Hokkaido Salmon Hatchery No. 17
Furthermore, they are spawned and hatched in freshwater streams or lakes.

They havea strong home instinct, practically all of them are returning to spawn in their motherstreams of origin or in the adjoining districts within limited extent. The spawning is
operated in some suitable gravel beds where the fish bury their eggs to protect them frommany predators or other elements in the streams. The spawned eggs hatch in the gravels
and the fry live there for a time absorbing the nutriment from yolk sac attached to their
belly.

When the yolk is consumed early in the following spering, the fingerling emerge

from gravels and begin to swim about actively in the stream.

2.

Osteological structures of the Chum salmon (0. keta).

Since the beginning of the last century, the studies on the skeleton of fishes have beenmacle by many zoologists, since the skeleton is one of the important characters in thefundamental structure of the body for the classification among genera and more higher
categories.

I%%),

Among them, of especial importance are those published by Giinther (1866,

Boulenger (1904), Hertwig (1906), Goodrich (1909) and Vladykov (1954) who haveadded many precious contributions to our knowledge of the skeleton and anatomy of somespecies of salmonid fishes. In comparative study of various fossile and extant fishes, Berg

(1955) have shown systematically their relationships, and described the osteological characters of Coregonus species of the Salmonidae. Tchernavin (1923) also recorded the changeof skull in breeding seasons of salmo and qqcp-hynchus. According to him, they show
so much resemblance that the bones of the genus Oncorhynchus are not easily distingu-

ishable from those of other species, and the lack of sharply defined characters may be
attributed to their recent origin. T h e writer wishes to describe here the skeleton of the chumsalmon (0. k d a ) as a representative of the genus Oncorhynchus which are abundant in
Hokkaido.
T h e skeleton is generally divided into an axial and appendicular skeleton.
T h e order therefore indicates from the cranium, afterwards the reminder constituentsof the skull, then on the vertebral column and unpaired fin and finally the paired fins andtheir girdles.

A)

Axial skeleton-Thisis the most important part of body, consisting of two partsof skull and vertebral column.
1. Skull-The skull composed of the cranium, forming brain case in which the brain
is contained, and a lot of facial bones.

C~aniz6nz: (Figures 13-18)
It is a highly important character that the cranium yet keeps the feature of the primor-

dial cranium as in that of the elasmobranchii. l n the cartilaginous cranium, fat masses arescattered everywhere in various forms, especially abundant in posterior part except the
rostrum. In the adult male of spawning season, the rostrum of the cranium is much elongated and more or less curved and bear a knob at its apex which is attached to the premaxillaries on each side. On the cranium several cartilaginous and membranous bones
are formed as follows. On the upper part of cranium the following bones are seen; thenasal, mesethmoid, prefrontals, frontals, parietals, supraoccipital, epiotics, sphenotics, pterotics
6

Ecological and Morphological Studies of the Genus Oncovhj..nchu;

and opisthotics. The bones placed on the lower part are vomer, parasphenoid, basioccipital,
orhitosphenoids, alisphenoids, prootics, opisthotics, exoccipitals, sphenotics and pterotics.
when the bones described above are completely removed from the cranium, the featuresof cartilagenous cranium becomes more or less as irregular, but the main body is held
almost in original form and identified in respective parts of its body as brain case, orbit,
auditory and nasal cavity and even in the attached places of many bones.

Basioccipdal : (Figures 34, 36-39)
A stout bone, rather long, almost hexahedron in form, partly cartilagenous in front,
and bearing the single concave occipital condyle for the cranium of the first vertebra, atlas.
About it a small region of the floor of the foramen magnaum is constituted. Mid-ventrally
it exhibits a deep groove to which fits the posterior terminal portion of the parasphenoid.
T h e canal constructed by this bone and the parasphenoid is a passage for eye muscle.
thin process on dorsal side is inserted into rear part of both prootics.

A

The basioccipitalis bounded above by the exoccipital, laterally by the prootics and below by the parasphenoid.

Exoccipital : (Figure 39)
A pair of very thick bone with nearly tetrahedron is shape. It is completely ossified,cartilagenous in front and upper side, and forms latero-ventrally most of the occipital foramen or foramen magnum.

Each exoccipital bears a prominent and concave facet called

paroccipital condyle, for the corresponding process on the atlas.

T h e exoccipital is bounded

above by epiotic, laterally b y opisthotic, in front by the prootic, and below by the basioccipital.

It hears a conspicous foramen transmitting thevagus nerve, and also a small porefor the first spinal nerve.

Su-bmoccipital: (Figure 27)

It is placed in the front far from the foramen magnum. A larger cartilagenous bone,almost square in form on dorsal side, and thick bone constitute the posterior part of theprimodial cartilage.

Its basal part is surrounded with much cartilage, and owing to its

form being directly the upper wall of tlie brain case, and when this bone is removed, anearly square pore is opened at upper part of the brain case.

The supraoccipital crest ari-sing from central part of it moderate, not long, rod-like extends backward, its posterioredge is branched into about three.

Along each side of the bottom of this bone depressionsof anterior semicircular canals are formed.

The supraoccipital is bounded in front by thefrontals, laterally by the parietals and epiotics.
The auditory capsule of Oncurhynchus is formed by the following five hones as inother fishes.

Sphenolic or post frontal bone: (Figure 21)
Small stout bone, irregular in form, its basal part cartilagenous contains many small
fat masses, downward reaching to articular groove for hyomandibular. This bone forms
a process on the posterior wall of the orbital cavity.

The sphenotics are bounded aboveby frontal, below by the alisphenoid and prootic, and behind by pterotic.

Proolic or @ t r ~ ~ a(Figurel:25)
Nearly pentagonal thick, stout bone surrpounding by a quantity of cartilage, upward7

Scientific Reports of the Hokkaido Salmon Hatchery No. 17
extending to the articular groove for hyomandibular. Just in front of this bone it is perforated by the large canal or foramen transmitting the trigemino-facial nerve and also by
smaller jugular and carotid foramen.

It is bounded by the parasphenoid, alisphenoid,

sphenotic, opisthotic, exoccipital and basioccipital.

Efi'otic : (Figure 22)
Stout bone, irregular in shape, its basal cartilage with many small fat masses. I t bears
a strongly large process which are attached to the upper limb of the posttempral.

is the posterior semicircular canal passing through the basal part.

There

I t is bounded by thesupraoccipital, parietal, pterotic, opisthotic and exoccipital.

Pterotic : (Figure 24)
Elongated bone, irregular in shape. It bears backward a long process which is called
pterotic process.

Laterally it has about half of the anterior of the articular groove for thehyomandibular.

There is a trace of the part of the horizontal semicircular canal along theinner side of the bone.
and prootic.

It is bounded by the sphenotic, frontal, parietal, epiotic, opisthotic

Opisthotic or intercalar : (Figure 23)
Nearly rectangular small bone, one arm of it forming a part of the upper wall andthe other one the hind wall of the cranium.

It bears a preocess produced from the angle

which attached the lower limb of the posttemporal. It is bounded by the epiotic, pterotic,
exoccipital and prootic.

Parietal : (Figure 20)
Flat small membrane bone containing no cartilage, right and left parietal separated
by the intervention of the large supraoccipital covered by the terminal portion of the frontals.

The parietal is bounded by the frontal, supraoccipital, pterotic and epiotic.

Alisphenoid : (Figure 26)
Small, almost oval bone, containing thick cartilage with many small fat masses in thebasal part.
the

It forms the anterior boundary of the eye muscle canal and the foramen fortrigemino-facial nerve.

It is boundedby the parasphenoid, prootic, sphenotic andfrontal.

Orbitosphenoid : (Figure 34)
Rather small, almost square bone, the right and left bone closely fused together with
the inner surface seen as one bone.

They are located just in front of the brain case between

both orbits, these bones spongenous, not only contain many small fat masses but also in
the interspace between both bones and the basal cartilage.

There is an entrance transmi-

tting two optic nerve, on the posterior middle wall of these bones but this entrance divided
into two canals, on the way through these bones. The orbitosphenoid is bounded by theparasphenoid, aIisphenoid, frontal, prefrontal and cartilage.
Frontal : (Figure 33)
T h e largest polygonal membrane bone with a longitudinal curved ridge along the medianpart and covering the interorbital region. The dorsal and the ventral surface are rugged,
cartilaginous containing many fat masses; the right and left frontal are separated by the8Ecological and Morphological Studies of the Genus Oncorhynchus

median intervened cartilage. The posterior marginal part of the frontals overlapped theposterior parts of the supraoccipital, parietal, sphenotic and pterotic, while the anterior
parts covered by the mesethmoid. T h e frontal is bounded by the mesethmoid and prefrontal, behind by the sphenotic, pterotic, parietal and supraoccipital.

Prefrontal: (Figure 32)
Small, thick, almost head-gear like bone, located between the orbit and nasal cavity,
the basal part of which is cartilaginous wall of the orbit and articulating the palatine,
unlike other fishes it is not perforated by a foramen transmitting the olfactory nerve. T h e
prefrontal, w h k h is called by other authors ectethmoid, lateral ethmoid, parethmoid orpaired ethmoid, is bounded by the nasal capsule in front, by the frontal above and thepalatine below.

T h e orbit is bounded by the prefrontal, frontal, sphenotic, prootic, paras-

phenoid, alisphenoid, orbitosphenoid and cartilage.

Mesethmoid : (Figure 30)
A large thin triangular bone, more or l e s s emergination on the posterior margin, placedon the dorsal side of the basal part of the rostrum, just in front of the frontals and it isalso in opposite to the anterior part of the vomer of the ventral side, its terminal portion
overlapped to the anterior region of both frontals. T h e mesethmoid is bounded behind by
the frontals, further the nasal near the posto-lateral side of it.

Nasal: (Figure 31)
One of the smallest membrane bones, placed over the nasal cavity, just in front of thelongitudinal medial ridge on the frontal.

On the anterior part, small two nerve pores

opening for the nasal chamber and also a large one for the entrance of the olfactory nerveon the posterior end.

by the prefrontal.

It is bounded in the above by the frontal and mesethmoid, behind

It is sometimes celled the turbinal.

Vomer: (Figure 28)
A large, ship-like, unpaired membrance bone divided into a anterior part and a posterior shaft, the ventral surface of the anterior part is flat but its dorsal side has a keel-likeridge fixed to the cartilage, the posterior shaft concave lodging into the concave cavity of
the anterior part of the parashenoid and it has a median high ridge which bears vomerian
teeth arranged in a single series. T h e vomer is bounded by the parasphenoid behind.

Parasphenoid : (Figure 29)
A very large, ship-shaped, triangular membrane bone and also the appearance of thisbone is cruciform, so as to produce triangular process on each side from near middle part.
On the cross part, there are four small pores for the blood vessel, the anterior part of it
covered by the shaft of the vomer, as already mentioned above, the posterior portion grooved along the dorsal side and it fits each other with the groove of the ventral side of thebasioccipital, then, there a canal for the eye muscle constructed, its posterior end concave
and nearly reaching to the occipital condyle. The parasphenoid is bounded by the vomer,
orbitosphenoid, alisphnoid, prootic, basioccipital and exoccipital.
T h e plate-pterygoid arcade. (Figures 11-12>

Hyomandibular :9

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

It is a broad cartilaginous bone, the head of this bone which is very cartilaginousarticulates with the long articulate groove which stretches along the bases of the sphenotic,
prootic and pterotic, the lower portion of the shaft of the hyomandibular cartilaginousarticulates to the symplectic and interhyal, the posterior projection articulating with thehead of the operculum and also it attached with the upper part of the preoperculum behind and metapterygoid in front.

The hyomandibular is hounded by the operculum, metap-

terygoid, sphenotic, pterotic and prootic.

Symplectic
Small rod-like bone, its head forms with the shaft of the hyornandibular the cup forthe upper end of the interhyal and also bears a cartilaginous epiphysis.

Its head portionis attached to the metapterygoid in front and its upper posterior edge to the preoperculum.
Ventrally its lower part is wedged under the quadrate.

The symplectic is bounded by thehyomandibular, preoperculum, quadrate and metapterygoid.

Quadrate :Nearly triangular hone, the upper part cartilaginous : it bears posteriorly a strongly
calified spine attached with the preoperculum.

In front it articulates with the pterygoid

above the metaptrygoid and below its free extremity bears a stout knob articulating to thearticular of lower jaw.

It is bounded by the pterygoid, metapterygoid, symplectic andpreoperculum.

Metapterygcid :Nearly triangular bone, its lower part cartilaginous.

It is attached to the hyomandihularabove, the symplectic, the quadrate below, and rnesopterygoid.

Mesoptmy goid or cntoptery goid :A thin leafy bone, almost without cartilage. It is attached to the metapterygoid behind,the pterygoid and palatine below.

Pterygoid or ectopterygoid :An elongated bone and more or less curved without cartilage. It is attached with thepalatine in front, the mesopterygoid above, and the quadrate behind.

Palatine :A rather elongated bone, bearing a high ridge along the dorsal side. It has a large
cartilaginous mass on the anterior part of this bone, the mass hears two processes whichis articulated for two processes of the nasal capsule of the cranium respectively and also
the lower process of the mass contacting with the maxillary.

The thin cartilaginous platearises from the posterior part is elongated backward and continue from under the mesopterygoid to the symplectic.
along the lower edge.

The palatine bears canine-like teeth (ca. 11) arranged in a series

It is attached to the pterygoid behind and mesopterygoid above.

T h e jaw apparatus. (Figures 11-12>
Bearing a saddle shaped articular surface for the quadrate, behind which it send up a
prominent i. e. post-glenoid process.

The bone is stoutest at this region, but becomes

gradually lameliform forwards, and its anterior margin is furcate, the lower limb fitting
to that of the dentary, the upper limb larger inserts to the curveture of the inner side ofEcological and Morphological Studies of t h l Genus Oncorhydzus
the dentary.

The outer face of the articular is convex, the inner concave.

Angular :T h e smallest bone, roundish among the other bones of the skull, situated at the posteroinferior angle of the articular.

MeckeE's cartilage or mandibular cartilage :It is a very long roundish rod or cartilage, lying along the inner side of the articularand its anterior end reaching almost to near the anterior extremity of the dentary.

Dentary :A thin, elongate membrane bone, but well ossified anteriorly and strongly attached tothe dentary of the other side, by the symphysis.. It is forked behind and contains a large
triangular cavity for the reception of the limb of the articular.

Like the latter, its outerface convex and the inner concave. Along the upper edge, canine-like teeth arranged in aseries, and the anterior several ones are more larger than the posterior teeth and curved
at the terminal part, backward.

when the mouth closed, the tip of the lower jaw fits tothe palate of the upper jaw behind the inner lip.

Maxillavy :An elongated membrane bone and forms dorsal part of the gape as the premaxillaryin the upper jaw.

T h e anterior part attached to the lateral side of the cartilaginous cranium

below the nasal cavity, but the posterior part free covers a part of the lower jam and theoblong small supplemental bone attached on the terminal part.

Along the lower edge

canine-like teeth arranged in a series and they are smaller than those of the premaxillary.

Premaxillary :A smaller membrane bone, situating in front of the mexillary. On the spawning season,that of the adult male prolonged and curved accompanied with the prolongation of therostrum of the cranium but on the female it is nearly not prolonged.
are larger than those of maxillary.

Teeth on this bone

There are about eight teeth in number and more orless cnrved at the terminal part.
T h e opercular bones. (Figures 11-12)

Operculum or opercle :A thin, large, laminate membrane bone containing no cartilage except at the cup whicharticulated with a process on the posterior margin of the hyomandibular.

T h e posterior

margin roundish and its lower part overlapping the suboperculum.

Subopercdum :A leafy membrane bone, thinner and smaller than the operculum, the posterior margin
also roundish and the upper and lower part overlapped by the operculum and interoperculum.
T h e operculum and suboperculum support the posterior free margin of the opercular fold.

fnte~operculum:
A thin membrane bone but stouter than the suboperculum, it stiffens the ventral
margin of the opercular flap,

Its marginal edge also roundish and the posterior partoverlapped the anterior part of the suboperculum, and the anterior part of the interoperculum and operculum laying under the preoperculum.

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

Preoperculunz 1
A thickish semilunar membrane bone. This is ususlly considered to be a modified
lateral line bone i. e. a bone developed primarily around a portion of the lateral line system

and is therefore probably not homologous witht:i ,?t her opercular bones. It is closely
connected with the hyomandibular, symplectic and almost completely covers the interhyal.
I t ts the stoutest of the opercular bones, the posterior part roundish overlapped the operculum and suboperculum and interoperculum.
The orbital bones. (Figure 12)
The orbital bones are composed of preorbital, suborbital and supraorbital. T h e preorbital bone is the smallest in the orbital bones attached the first suborbital bone behind.
Thp suborbital or infraorbital consists of seven bones in number, and these bones conjoined
each other, the first and second suborbital more elongated than the prefrontal.

T h e third,

fourth, fifth, sixth and seventh suborbital bone notably laminate situated behind the eye
and their posterior ends reching to front of the preoperculum, the uppermost seventh suborbital attached to the sphenotic. T h e supraorbital bone about oblong attaching to thelateral edge of the frontal above eye.

The eye is surrounded by the preorbital, supraor

bital and these bones protecting the eye.

There is no sensory through the orbital bones as

seen in other teleosts.
The hyoid apparatus. (Figure 49)
T h e hyoid arch is an apparatus of the visceral skeleton, composing of partly cartilage
and partly carcified bone.
Glossohyal

A median anteriormost element of the hyoid apparatus bearing large cartilage on thebase, is oblong in form, directed horizontal forward, the posterior part is loosely attachedto the anteriormost basioccipital and hypohyals.

On the dorsal side, several canine-liketeeth arranged in two series.

Hypohyal :A short rodular bone, bearing also large cartilage on the basal part and it loosely
articulating in t h e middle line with the same element of the other side. In front, it united
with the glossohyal and anteriormost basioccipital and behind the ceratohyal.

Ceratohyal :The ceratohyal is very large nearly rectangular in form, intervening between the epihyal
formed the main part of the hyoid arch together the epihyal. T h e upper and lower marginof the bone shallowly concave. T h e anterior and posterior part of the bone cartilaginous,
attached to the hypohyal in front and epihyal behind.
Eflihyal :It is of a somewhat triangular form, containing cartilaginous tissue in the surrounding
part and attached to the interhyal at the upper posterior end. T h e upper margin nearlystraight or slightly concave but the lower margin roundish, it is truncated anteriorly andseparated by a narrow cartilaginous interhyal from the ceratohyal.

Interhyal or stylohyal :I2

Ecological and Morphological Studies of the Genus Oncorkynchua

The interhyal or the dorsalmost ossification of the hyoid apparatus is of small rod-like
form, directed, tipped with cartilage and fits into the cupshaped articular facet between
the hyomandibular and symplectic. T h e lower end of the bone firmly attached to theupper posterior end of the epihyal.

Urohyal or interhyal ;The urohyal is a elongate unpaired bone, placed between the right and left hyoidarch and invested in the muscle of the isthmus.

T h e anterior end of this bone securely

fastened, by the muscle ligament, with the tip of the lower surface of the anteriormost
basibranchial and both hypohyals, this is longer than the length of the ceratohyal.

Theanterior part is a rod-like form but the posterior part becomes gradually thinner and wider,and bears a high ridge along the median line, therefore formed deeply groove along eachside of the ridge and sharply pointed posteriorly.

Branchiuslegal rays
T h e branchiostegal rays belong to the membrane bone.
(12-16)

They are mostly thirteen

in number, ususlly five of them are borne by the ceratohyal and the remainderby the epihyal.

The rays are always laminated and curved, diminishing progressively inlength from the back to forward.
T h e branchial arches. (Figures 46-48)
The branchial arches is an apparatus of the visceral skeleton composing of four basibranchial and five paired of the branchial arch, these elements are of partly cartilage,
partly calcified bones. T h e basibranchial consists of four elements.

T h e first basibranchial
A nearly rectangular hone, attaching in front with the glossohyal and hypohyals andbehind with the second basibranchial and hypobranchials of the first branchial arch.

T h e second basibranchial
Its form is as similar as the first basibranchial but slightly short and more or lessconcaved on each side, attaching in front with the first branchial and hypobranchials of
the first each and behind with the third basibranchial and hypobranchials of the secondarch.

T h e third basibranchial :A narrow laterally compreseed bone, attaching in front with the second basibranchialand hypobranchials of the second arch and behind with the fourth branchial and hypobranchials of the third arch. T h e first, second, and third branchial as above mentioned,
formed on the median rod-like cartilage.

T h e fourth basibranchial :An elongated cartilage bone, wedged in between the bases of arches 111 and 1 V . There
are only three segments in the arch, while the first, second and third arch bearing
four segments. It is obvious that basal segment of this arch is homologous with theceratobranchial. Hence the basibranchial may represent either the two vestigial hyposegments fused together or it may have been formed by the basi-and two-hypo-elements
fusing up.
13

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

The first branchial arch:
I t is consists of four elements i. e. the hypobranchial, ceratobranchial, epibranchial andpharyngobranchial.

The hypobranchial nearly rectangular, attached to the cartilage between

the first and second basibranchial. The ceratobranchial and epibranchial elongated. theceratobranchial is deeply grooved ventrally for the blood vessels.

The epibranchial notchedon the posterior end, the pharyngobranchial is very small rod-like bone attached to theprootic region of the cranium.

The second branchial arch :It is constructed by the four elements as the first branchial arch.
branchial attached to the cartilage between the

The head of hypo-second and third hasibranchial.

Theepibranchial and pharyngobranchial produced a process respectively on the posterior end,
the posteriormost element is the smallest in all the elements.

The third bvanchial arch :It is also constructed by the four elements as the first and second branchial arch.
T h e hypobranchial fixed with the third and fourth basibranchials, the epibranchial andpharyngobranchial produced a process respectively on the posterior part as the second arch.
T h e posteriormost el.ement is longer than those of the first and second arch.

The fourth branchial arch:
There are only three elements i. e. the cerato-, epi- and pharyngobranchial but thehypohranchial absent, as already mentioned. The head of the ceratohyal attached with thefourth basibranchial peculiarly roundish and the pharyngobranchial very small with canine-

like teeth which called as the upper pharyngeal teeth.

The f i f t h branchial arch :This is more reduced than any of the other arches and consists of a single bone oneach side. T h e inferior pharyngeals are stout, elongate bones separated each other.

Oneor two irregular rows of canine-like teeth are borne on the pharyngeal surface, these teeth
are called usually as the lower pharyngeal teeth.

Gill-rakers 1
The gill-rakers are produced along the inner surface of the hypo-, cerato- and epibranchial. These diminish both in size and number from before backwards, their function isto provide a rough filtering apparatus for the water passing out of the pharynx and protected the food might easily escape through the gill slits.

They are purely dermal and are

not fused on to the arches. The number and postion was in the specimens examined, nearly
constant and symmetrical, the following table denote the number and length of the gillrakers on every arch.
Rranchial arch
No. of gill-rakers

I

n

E

Iv

V

20-27

19-23

16-21

13-15

7-10

9-11

5-8

4-6

3-4

2-3

Length of gill-raker(unit: mm.)

Gill-lamellae :T h e gill rays, gill-filaments or gill lamellae are supported by series of very delicate
14Ecological and Morphological Studies of the Genus Oncorhqnchus

fragile gill rays fused together by their bases like a comb. They radiate out from thebranchial arches as usual and occur in pair. On the basal part, the inner and outer lamellae
are 111-117 on the first arch, 138-147 on the second arch, 141-147 on the third arch, 139
on the fourth arch, but no gill lamella on the fifth arch.

The vertebral cslumn : (Figures 10, 40-45)
The vertebral column of the salmon may be divided into a trunk (or abdominal) andtail (or caudal) region only, distinguished in the former by the presence of ribs and in thelatter by the haemal spine. Each vertebra is markedly amphicoelous, the anterior andposterior faces being considerably scooped out in the form of a cone, the two cones being
connected in each vertebra by the pic-hole notochordal canal (canalis dicentralis). As allthese spaces are occupied by the remain of the notochord, the latter is absolutely continuousfrom one end of the column to the other.

The vertebral column nearly straight and bears

many low, longitudinal ridges on the surface.

The first vertebra or atlas:
The first vertebra called as atlas bearing a neural spine on the dorsal side and a paired
ribs on the ventral side of the centrum. It has two cartilage capped facets anteriorly forarticulating with the paroccipital condyles of the exoccipital. The anterior face of thecentrum also articulates with the single occipital condyle on the basibranchial, the connectionof the skull with the vertebral column by means of :j condyles being therefore very strong.
There is no transverse process and only rib, the head of rib embraces a small cartilagebone fixed in the r a c e s of the ventral side o f the centrum, the shaft very slender extending
downward along the inner wall of the body cavity, but from about the thirty-third vertebra
the transverse process arises and gradually backward increased in length, the ribs in thisregion attached with thses processes, transverse process of about the 39th to 41st vertebrae
forming the haemal arch on the ventral side. In addition there is an accessory rib orintermuscular bone attached to the neural arch and extending backward and outward into

the body muscle. It present about to the twenty-fifth vertebra.
spine fixed in the recess on the dorsal side of the centrum.

The base of the neuralT h s neural and hawzal spines :The neural and haemal spines are simple in structure and always furrowed longitudinallyfor the reception of the large vertical sheet of ligament connecting them with each other.
All the spines included backward. On the basal part of the neural spine, there is theneural canal for the spinal cord and also the haemal canal for the caudal artery and veinon the basal part of the haemal spine.

T h e zygapophysis :There are particulary noticeable elongate stout zygopophyses which are hardly attachedto the inner side of the neural arch and also fixed with each other but these zygapophyses
entirely lacking after about thirty vertebra.

The notochord :A s already mentioned, all the vertebrae have a notochordal canal except the last andthe cone-like space in the vertebra which is occupied by the remain of the notochord. The
15

Scientific Reports of the Hookkad Slamon Hatchery NO. 17

terminal portion of the notochord, the so-called “Urosty1e” projecting backward and upwardfrom between the penultimate and last vertebra. It is yet unoccified, rod-like in form, about

19 mm. in length, bearing many segmental marks and the distal end reaching to the basal
part of fin rays. The urostyle is attached by these bones partly overlapping each other, thebasal bone is larger plate-like, probably transformd from neural spines of the terminal tm-o
vertebra except the last but the other two bones are much smaller andelongate. On theventral side of it, there are two small uppermost hypurals overlapping each other, the outer
one being larger and the anterior end of these bones forked and embracing the urostyle.
Just above it the epural bones are situated.

The caudal fin and extremity of vertebral column.

The caudal f i n : (Figure 52)
T h e caudal fin of the salmon belongs to the homocercal fin. On the terminal part ofthe vertebral column, there is found an expanded fan-shaped plates, added the neural andhaemal spines of the last five vertebrae and their free surface articulating with caudal fin
rays. The last vertebra is used together with the third upper hypural, hence looking likeone.

As already mentioned, the urostyle turns uIj backward and upward from between the

penultimate and last vertebra. Wedged in between the urostyle and last neural spine are
two partly cartilaginous bones which are closely connected by ligament with each other andwith the last neural spine, but which are not sufficiently long proximally to reach the vertebral column.

They are usually called the epural or epiural.

The hypural bones plate-

like being cartilaginous distally and strongly ossified proximally.

Each bone in the tailgiving articulation to fin rays bears a thin terminal carilaginous epiphysis. As in the otherfins there is a pad of subcartilaginous tissue intercalated between the bones of the vertebral
column and the proximal ends of the fin rays. This is embraced by the diverging halvesof the rays. T h e number of the caudal fin ray varied in the specimens examined around
41 to 44 rays in all but the developed rays always constant are 19 rays in number.

B ) T h e appendicular skeleton.
The dorsal fin: (Figure 50)
As in the paired and caudal fins all the fin rays consist of two pieces. Each fin rays
is connected with two further skeletal pieces termed the haseost and axonost. The axonostis called the interspinous or interneural bone, on account of its position between two neuralspines, whilst the baseost is always situated between and attached to the heads of tm-o halvesof the ray diverge proximally and tightly clasp the baseost which is small rod-like bone.
First axonost supports the first and second rays. The first and last axonosts have an
extraordinal shape respectively and stouter than the others. Each fin ray has six muscles,of which there are three on each side. These muscle composed of the lavator, flexor andlateral muscle, the elevator muscle arising from the anterior surface of the head of the fin
ray and being attached on the shafts of the adjacent two axonosts, the posterior flexor
muscle arising from the posterior surface of the ray and being attached on a shaft of theaxonost of just below the ray i. e. two muscles above mentioned arranging in before andbehind hut anterior about four flexor muscles (2nd to 5th) overlapping on the elevator
16Ecological and Morphological Studies of the Genus Oncovhynchus

muscles.

The elevator muscles are always larger than those of the flexor.

The elevatorand flexor muscles of the first ray are very small and attached on the first large axonost.
T h e lateral muscles arise from the head of fin ray, and being attached to the inner sideof the skin, they act to move fin rays to right and left direction. There are two muscular
bands connecting the posterior end and the first axonost and also a muscular band connecting the last stout axonost and the adipose fin.

In front of the dorsal fin there are 21

to 23 interneural spines arranged in a series and distributing one between each neuralspine, the first interneural spine situated between the second and third neural spines.

The anal f i n : (Figure 51)
T h e mechanism of the fin rays and their skeleton supports is the same as in the dorsal
fin. The axonosts are sometimes called interhaemal spines to distinguish them from theinterspinous elements.

The structure of the anal axonost is nearly square in front view.

There are two elevator muscular bands connecting its anterior face and two processes ofthe pelvic girdle and also two flexor muscular bands connecting the last baseost and thelower origin of the caudal fin.
The pectoral girdle and fin. (Figure 53)

The pectoral girdle :It is composed of the clavicle, postclavicle, supraclavicle, scapula, coracoid and mesocoracoid.

T h e clavicle or clitherum :A large curved bone. The upper part of handle is stout, attached to the inner surfaceof the lower part of the supraclavicle and bears a thin lamina behind, overlapping theanterior parts of postclavicles. T h e outer surface of clavicle body is specially expanded andconcaved. T h e elevator and flexor muscle arising from the base of the pectoral fin is
attached with the clavicle and coracoid. Below, the clavicle is connected in the midventral line with the clavicle of the other side, by a symphysis.

T h e postclavicle :It consists of two small laminate bones arranged in a series, the anterior parts ofthese bones are overlapping by the clavicle, and the upper bone is oblong in form and thelower one prolongs downward extending to under of the pectoral, its upper extremity attaching to the upper bone. Its position is partly indicated externally by a scar vn the skin.

The supraclavicle :A elongate bone, thin below but stouter above. Its lower part overlaps the clavicle
and upper postclaviele, and above it ts overlapped by the posttempral. On the upper
extremity it has a small prominence which fits to the under face of the lower limb of theposttemporal.

The posttemporal :It is also elongate stout bone, called the suprascapula. From the lower part it projects a limb forward, the upper or epiotic limb is articulated with the supraoccipital andepiotic, the lower or parotic limb is smaller and shorter, connected by a ligament with theopisthotic only.
17

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

The scapula :It is rather small roundish cartilaginous bone attached to the inner side of the clavicle.
There is a larger scapular fenestra for the first spinal nerve. It is bounded by the clavicle,
postclavicle, coracoid, mesocoracoid and the base of the pectoral fin.

The coracoid :An elongate laminated bone, separated from the scapula by the intervention of cartilageplate between these two bones.

It is attached with the clavicle on the upper and anterior

parts which are cartilaginous.

A ventral spine projecting from the posterior exterimity

backward.

The mesocoracoid
An U-shaped bone, attaching to the clavicle, scapula, coracoid and cartilage-plate on
the inner side.

Thence, it is bounded by the clavicle, scapula, coracoid, postclavicle andcartilage plate.

The radials:
Consist of four small rod-like bones, attaching to the posterior extremity of the scapula,cartilage-plate and coracoid.

The basal part of fin rays diverge and embrace the extrem-

ities of the scapula and four radials.

T h e uppermost one is the shortest and gradually

downward increasing length.

The fin r a y s :There are 14 to 17 fin rays in the pectoral fin. Each ray consists of two pieces enclosing
a central core of soft tissue as commonly occurs among teleosts.
segmented for the greater part of its length.

Each ray is completely

The two portions of the ray diverge at thescapula-coracoid articulation and embrace its subcartilaginous pad as already described.
The pelvic girdle and fin. (Figure 54)

The pIoL2ji.c girdLC :A nearly triangular bone, situated below the dorsal fin. T h e right and left pelvic
bones are attached at the anterior and posterior parts of the inner side.
region of it is thickish and stout, but the forward part thinnish.

The posterior

There is a long ridgealong the outer edge and also posteriorly a small process which is situated between theelevator and flexor muscles.

On the posterior inner extremity a articular process presents,

opposite to that of the other bone and the cartilaginous processes projecting inward andbackward from immediately behind both the articular processes.

These small cartilaginous

processes are connected by two elevator muscles with the first axonost.

The fin rays :There are 10 to 12 rays in the ventral fin. These rays articulate with the pelvic bone
as in the case of pectoral fin. The fin rays resemble those of the pectoral fin, and eachconsists of two pieces but the first ray is only a piece, never bifulcated further, a rudimental ray on the innermost of the ventral fin.

3.

Morphological characters for species discrimination.
The morphological studies of marine and freshwater fishes have been carried out in

extensive degree by many authors for a long time, and in many of them they propose
18

Ecological and Morphological Studies of the Genus Oncorhynchus

1

keta

gor buscha
nerkatschawytschamasoukisutchrhodurus
kawamurae

1

3

7

11

26

76

82

51

23

6

3

1

5

13

34

37

22

11
3

6

17

10

34
30
20
3 1 2 1 6
6
5
4
2
2

11

7
2
8
7
2

3

4

12

16

18

1

2

1

5

1
1
19

6
2
1

1

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

keta
gorbuscha

1

1

8

8

179
180

181
182

4

4

1

8

5

183
184

185
186

187
188

9

5

2

6

6

8 1 1

8

7

7 1 0 1 2 1 0

Lateral line number
189 191 193
195
190 192 194
196

197
198

199
200

201
202

203
204

2

1

nerka
tschawytschamsoukisutchrhodurus
kawamurae
Speciesketa
gorbuschaMean
135.06

7

5

1

1

nerka
tschawytschamasoukisutch172.84133.41144.61129.40133.86

rhodurus
kawamurae

129.68131.33

range 147-204 has a considerable difference from that of other seven species,

Also, in the

chinook salmon, 0. tschawylscha, the range follows to that of gorbuscha, in having 137 to150. In addition, considering the mean of the species, keta, nerka, kisutch and kawamurae
are alike to the ranges of the lateral line, while masou and rhodurus closely resemble inrange patterns and scale numbers. T h e classification of species of the pacific salmon is,therefore, difficult with only the number of lateral line scale in view, but their ranges are
more available for distinguishing each species than with degree, especially the gorbuscha
and tschazuytscha in appearance.
(31 Number of fin rsys
The number of fin rays are often counted in many cases to the descriptive accounts offish taxonomy, but, as noted previously, the writer counted herein all elements of each fin
ray in this part.

The range and mean of fin rays, except caudal fin, in all species belon-ging to Oncorhynchus genus are as indicated in Table 2.
Table 2.

keta
gorbuschanerkatschawytschamasoukisutchrhodurus
kawamurae

1

Total counts recorded for Oncorh3nchus species.

3 42 79 30 8
1 4 22 36
4
1 21 25 16 2
5 16 11
6 19 37 24
16 7
2
1 3 8 2 3 2

1
1
2
6
1

1

'

13.96
14.66
14.00
15.29
15.08
13.44
14.65
12.50

~

1

20

18 85 64
3 32 3810 43
5 13
1 15 46 38
1
2 12 10 7
1 5 17 14
5
1

31
13
23
14
4
2

1
8

3

15.54
15.21
16.19
16.79
14.33
14.70
15.28
15.00

Ecological and Morphological Studies of the Genus Oncorkynchus

keta
gorbuschanerkatschawytschamsoukisutchrhodurus
kawamurae

17

2
1 13 341
6 8 8
219 87 46
3 27 32 6
11 30 21 2
5 6 1930 81
3 8 1 38 6
1 1

I 17.06
I

2

17.51
17.15
18.56
15.04
17.32
15.00
15.75

6

2

1
90
3
7
5

89
70
60
20
3
23
21

13
3
10
14

1

11

11.06
11.04
11.14
11.41
10.01
10.88
11.10
10.00

The consideration of fin ray of the species is, in general, overlapped in all species.
The fin ray cannot easily be distinguishable by its number in each species.

In the distinctionof species, the ventral fin of the masou salmon (0.
masou) is almost always ten in number,rarely nine or eleven.

Although the paired fin is mostly of equal number on both side,

the number have differs by one or two on each side. Furthermore, the pectoral and anal
fins of the chinook is greater in number than the other members of the pacific salmon.

Also the anal fin of the masou salmon includes to the same range group as the Biwa
salmon (0. rhodurus), and each of these two species much resembles this elements. As aresult of the observation, it cannot be readily distinguished from each species by fin countonly.

(4 Number and form of gill-rakers (Figures 55-61)
T h e form and number of the gill-rakers have been extensively used in identifying
many fishes. This element is also recognized to be adopted to the species of O n c o ~ h y n c h u ~(Ohta, 1918). T h e form of the raker is smaller in distal parts on the first gill arch thanthose on angle part of both upper and lower limbs, namely they gradually reduce its length
to edge direction. I n this part the writer made the comparative observations in regard tothese elements of eight species which are found in Japan and adjacent waters.
First of all, the raker of salmons is generally rather stout, more or less taper andpointed at the tip, and its base is almost truncate.

T h e form on the first gill-rakers of eachspecies may be grouped into roughly three types : in the first type is represented by nerka,

gorbuscha and KazuamuTa.,

having much more slender spear shape, pointed at tip andthicky between rakers than the other, nzasou and rhodurus including the second type, aremore short, blunt in shape and roughly invest the interspace between rakers, and finally,keia, tschazuyischa and kisulch shows the intermediate type, because their forms are lesselongate than first type and also more slender than second case. The inner surface of eachraker is too armed with uniserial or more fine spicles on each side, which are bearing
relatively lower number and small in size of masou and rhodurus, moderate number M a ,absent or minute in gorbuscha and nerka, but numerous, prominent with naked eye intschawytscha and kisutch.
on the other hand, the count of gill-rakers has the definite range by species.

T h e result

examined with 763 individuals is shown in Table 3.
By the below table, the number of the gill-rakers are divided generally into two21

Scientific Reports of the Hokkaido Salmon Hatchery No. 17
Table 3.

Number of gill-rakers in Onco~hynchusspecies.
-~~~

Species~~

14 15 16 17 18 1920 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 30 31 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 4 0 4 1 4 2 Mean

22.91

2 5 26 51 83 53 18 3 2keta

2 2 920323419 6 12
1 2 2 6121731162116 8 5 1 1

gorbuscha
nerka ( * )tschawytscha
masou ( * )kisutchrhodurus
kawamurae

2 41817 9 3
1 3 7 20 44 38 19 8 1
2 5 18 14 2
2 5 4 4
2

1

30.42
33.66
20.67
18.40
21.21
18.66
1 36.50~~(*I Includt

and-locked form.

~.

~~~~

keta
gorbuschanerkatschawytschamasoukisutchrhodurus
land-locked
nerka

22-24
32-35
35-39
19-23
17-19
21-22
19-20

21
29-30
34-36
18-21
18-19
21
19-20

18-20
26-28
29-32
18-20
17-19
19-20
18-19

14-15
18-2 1
22-24
13-16
14-16
15-16
14-16

8-9
10-12
13-14
7
7-9
7-8
8-1 1

32-34

30-32

28-30

19-20

10-12

I

89
126
145
87
82
87
86
128

T h e counts on each gill arch are considerably overlapped or continued among thespecies.

T h e species of Oncorhynchus are also divided into two groups from the total

number of each gill-raker, having greater number in gorbuscha and nerku and small
number in other species.

As shown by the two table above, the interspecific difference ofthe gill-rakers in adult form is rather remarkable, in spite of the fact that these may probably by regarded as the influence of environmental factors as food organisms.

Therefore,

this element is most important to distinguish the species within same genus.

(5) Number of branchiostegal rays
The branchiostegal numbers is often used for identifying the higher categories of fishgroups.

Therefore, the writer has examined whether this element is useful to identify
22

Ecological and Morphological Studies of the Genus Onco~hynchus
closely related species.

Table 5 indicates the variation ranges of the branchiostegals

observed.
Table 5.

Number of branchlostegals in Oncorhqnchus species.
-~

~-

~~

Branchiostegal rays
~~

10

11

12

13

14

15

16

30
63
21

103
34
56

a4
2
27

25

4

17

ia

19

20

Mean

~~

keta
gorbuschanerkatschawytscha

1
1

3
16

8

masou
kisutch15

rhodurus

62kawamurae

46
57
24
4 1 7 2 0
15
22
4
1
. .

5
4
3
5

8

22

2

1

16

15

1

13.44
12.17
12. a2
17.50
12.68
13.73
12.20
11.85

From the results of this observation, it is evident that the range of branchiostegals is
usually all overlapped in each other, with the exception of chinook salmon.

The chinook

salmon, 0. tschazuytscha, has always greater number of branchiostegals which ranges from15 to 20 than other species here observed. In the pacific salmon the form and number ofbranchiostegal rays show no differences by the species.

This element is very convenient

to separate the chinook salmon from the other species, but cannot be used to distinguisheach species as a whole.

(6! Number of vertebral column
The vertebral count which forms a series of the segmental bones of body has beencommonly used by most authors as one of the important characters in taxonomic andecological investigations.

This element is also known undergo in some extent the influenceof the environmental factors such as a water temperature.

As minute processes are prod-

uced in ventral side of several vertebral centrum in front of the anal fin, the border
between precaudal and caudal parts give often rise to question.

As to these processes,

Clothier (1950) states that the first haemal intermediate to these process gradually becomelarger on succeeding vertebrae.

Recently, Seymour (1959) recorded in a part of his papers

that the vertebra with a process referred to the caudal vertebrae based on his study on
the chinook fingerling.

However, as paired ribs attached to tip of process, the writer

wishes to consider these elements to belong to the abdominal or precaudal vertebra.
T h e number of individuals used for this study are 137 and the results of mesurements
are shown in Table 6-a. In the light of these data, it is evident that the greater part ofcount range almost all overlappes in the precaudal and caudal vertebrae of each species,
with the exception of the data from two species, masou and tschawytscha.

of the precaudal

range, masou is slightly disparsed with smaller number than other species, and rhodurus

also shows the same tendency as masou.
Though a similar overlapping range was found, tschazuytscha shows no high numberof vertebrae.

On the other hand, the evidence regarding the total number is remarkableas shown in Table 6-b. They are generally grouped into three classes.
23

The first group

Scientific Reports of the Hokkaido Salmon Hatchery No. 17
Table

Number of vertebrae recorded for each species of Oncorhqfichus.

6-a.

~~~

~~

Vertebral number
Precaudal

Speciesketa
gorbuschanerkatschawytschamsoukisutchrhodurus

toki shi r a mhime-masu

37

38

39

2

2

40

5

2

2

1

9 1 1
8
1
1
2
7
4
2
1

1

5

I

41

42

43

4
5

1
1

1

1

4
1

0
2
5

I

Caudal

25

26

27

28

29

30

1

6
7
1 1 0
2
2

9
8

7
3

3
2

6

3
4
2

4
3

2
1

2
1

2
1

5
1

5

3
1

1
1

1

2
11

1

aeta
gorbuschanerkatschawytschamasoukisutchrhodurus
kawamurae
tokishirazu
himemasu

1

2

2
6

7 1 0
1
2

7

8

3

1
6

1

3

4

1

1

1

2

2

4
5

2
2

24

1

4

I

5

7
3

5

2

Table 6-b. Total number of vertebrae in Oncorhynchus species.
~ _ _ _
Species
63
64
65
66
67
68
69
70
71
72

-~
_ _ ~

31

Mean
68.75
67.27
71.41
64.82
66.85
65.57
67.50

5

i

66.81
67.28

Ecological and Morphological Studies o f the Genus Oncorhynchus

The interspace between folds shows a great difference by individuals, and by empty or fullconditions. However, the form of the transverse folds seems to be rather definite from
species to species: those of tschawyalscha is waving, and those of keta, kisutch and gmbuscha
are straight or slightly wave, while those of masou and rhodurus are chavezon in shape.
Furthermore, the fold of nerka is straight or slightly concave in form with one or more
subfolds occurring in the interspace between folds. In a few samples examined by meansof the binocular microscope, the folds in young and adult fishes showed a considerably
wide range in number between interspecies as given in Table 7.

Young

-_

34 (1)

37 (1)

32 (1)

34 (1)

Adult

32-43 ( 2 )

38 (1)

25-44(3)27-32(3)23-41(9)22 (2)_-__22-36 (3)On this basis it seems to be very difficult to take this character for distinguishing therelated species.

nFig. 1.

Diagrammatical sketch showing forms of transverse folds insome salmon fingerlings.
A. General aspect of the intestine. - 1. Anterior and 2. Posterior parts.
B. 0. gorhuscha ; C. 0. kisutch ; D. 0. tschatuytscha ; E.0. keta ;F. 0. rhodurus;

25

Scientific Renorts of the Hokkaido Salmon Hatchery No. 17cA

Fig. 2.

"I

Diagrammatical sketch showing different forms of the transverse
fold in the intestine in adult salmon.
A. 0. tschawytscha; B and C. 0. nerka;D. 0. gorbuscha; E. 0.keta; F. 0,
kisutch G. 0. masou ; H. 0.rlwdurus ;26

I

Ecological and Morphological Studies of the Genus Oncorhqnchus(8) The form and structure of scales
The body of the pacific salmon as well as other salmonid fishes are wholly covered
with cycloid scales, except a naked head portion.

Generally, a scale consists of exposedarea (or posterior) and conceal (or anterior), the latter possessing a focus near the center of
each scale and numerous circuli with concentric structure around the focus, whereas theformer is plain and smooth on its surface lacking circuli.

The scales show generally aconsiderable variation in size and shape according to various parts on the same body.
Therefore, for the scale reading, it is necessary to take the typical form of scale from thedefinite region on the body.

T h e figure, which is formed on the scale, is called “scalepattern” in proper : this has generally been used by several ecologists and ichthyologists
for ecological investigations, such as age-determination, scale-culculation, and growth-rateof the pacific salmon.

Since the scale pattern largely undergoes the influence of environ-mental factors such as water temperature, food nutriments and so on, they often exhibit
some different numbers of circuli within the limited range on a scale of the same species,
though of course there occur a basic difference according to life history of the species ofOncorhynchus.

T h e general outline of a scale is roughly roundish, ellaptical or oval inshape, being variable by species. Basically, both form and scale patterns seems to show
some differences by species as follows : masou, kisutch, nerka and tschazuydscha have usually
the so-called river zone, which develops by staying one or more years in freshwater, whileland-locked forms such as masou and nsrka show commonly on uniform growth.

T h e two

species, keta and gorbuscha, have scale patterns which are not recognized as the river zoneof the forgoing species on scale.
locked masou salmon.

Also, rhoclurus is closely related ecologically to the land-

The scale patterns on the scale surface is, therefore, of particularly

importance ecologically and is generally to be used as a remarkable indication to show
the life history of salmon. In short, the decision of each species is impossible by scale offingerling body, while it will generally be able to distinguish the species by means of scale
form and its pattern in the abult stage.

By these reasons, it may be unable to say thatthe scale character is wholly available for elassifying close related species.

19’; Number of the pyloric caeca
The pyloric caeca is a fring-like appendage of the digestive organ having a function ofnutriation, attaching to the junction between the stomach and intestine.

T h e form andnumber of the pyloric caeca are often prominent characters in identifying species of many
fishes.

In salmon groups, these elements are generally conspicuously small in number insome species, while in others numerous.

They are generally more variable in very wide

range, though highly differ greatly by species, than other characters such as vertebrae andlateral line scales.

In Table 8 is given the count range for several species of the pacificsa 1m o n .
From the table it is apparent that the number of the pyloric caeca overlapps or iscontinuous in a considerable wide range from species to species.

In spite of the above

feature, however, species under study can be divided roughly into two groups concerning
the number of the pyloric caeca.

T h e group which is characterized by a large number,
27

Scientific Reports of the Hokkaido Salmon Hatchery No. 17
Table

includes keta, tschawytscha, while8.

the second group chracterized bya small number are represented

1

speciesby masou, kisutch, rhodurus and~keta
gorbuschanerkatschawytschamasoukisutchrhodurus
kawamurae
tokishirazu
hime-masu

kazuamwae. The pyloric numbersof the pink, gorbuscha, and blueback, nerka, are generslly intermediate between the above two groTherefore, it is rather diffe-

ups.

Range in number of the pyloric appendage
in the species of Oncorhjnchus,_~_rent to clearly distinguish the species of Oncorhynchus by means of
the numerical difference of pyloric

Range

1

121-2 15
91-18880-117127-1 70
36-68
40-80
46-70
51-54
150-246
67-94

160.61
126.1991.00
159.61
47.05
62.60
58.00
52.50
185. a9
83.64
_ _ ~

~~

Mean

~

caeca.

UOI Form and number of the pseudobranchiae
The pseudobranchiae is a small
degenerated organ locating on the
inner surface of each preopercle hone
in a little concavity which lies behindthe strong transverse muscle forming
the roof of the pharynx.

However,

this organ rather well develops andis functional in more or less degreein the species of Oncouhynchus. The
proximal part of the gill-lamella ismounted with the membrane, whilecn..; :-.-.:-

it becomes free from the membraneat its distal region.

T h e pseudohra-

nchiae is also variable in shape frombeing nearly roundish to oblong inoutline.

In roughly speaking it israther characteristic in shape to spec-....

ies: it is fan-like in nerka, roundish

D
Fig. 3 Representatives of the pseudobranchiae.
A. 0. tschawytscha; B. 0. nerka (land-lockedform), C. 0. rhodurus ; D. 0. goybuscha ;in rhodurus and almost oblong in

gorbuscha, as shown Figure 3. The
Table

SpeciesNo. ofpseudobranchiae

1

I

9.

._..~.--.---A-

The number range of the pseudobranchiae i n the species of Oncorhynchus.

keta

13-19

I

1

gorbuscha

21-25

1

1

tscha
tschawy-

15-17! masou I kisutch 1 nerka I rhodurus

1

28

13-19

I

21-29

I

15-21

1

13-21

Ecological and Morphological Studies of the Genus Oncorhnjchus

number of the gill-lamella counted with a binocular microscope shows a wide variation to theconsiderable extent. The numbers mostly overlap from speciec to species as seen in Table 9.
Based on the above fact, it isdifficult to identify the species ofthe pacific salmon by means of thenumber of the pseudobranchiae.
Number ofappendicularscale

T h e appendicular scale or supplementary scale is a paired slender
one like appendage and attached tothe basal part on the outer side ot'
the first ventral fin ray,tapeiing

It has also abackwards at the tip.

longitudinal shallow furrow along its
middle line.

c

Generally its form is-different by different species, as well
as by individual within the same species. Also it differs in two sides of thebody.

In detailed comparison, it was

gorbuscha, nerka andfound that i;Gketa it is pointed in shape at the tip,S
tschawytscha
while in Y ~ Q ~ U Y Uandit is shorter with a blunt distal end.

Fig. 4.

T h e length range to the ventralc.

fin overlaps considerably within thespecies of Oncorhynchus (Table 10).

Length range of appendicular scale to ventral fin of the species of Oncorhjnchus.

Table 10.

Species
RanRefleft[rightSchematic drawing stawing different formsof the appendicular scale of the species.
A. 0. kisutch; B. 0. tschawytscha;0.
nerka; n. 0. masou; E. 0. rhodurus; F. 0.
keta ; G. 0. gorbuscha ;

1
~

keta

1.51-2.17
1.60-1.94

II

gorhuscha

1.68-1.96
1.93-2.23

I

i

~

nerka

2.12-3.42

1ltschawytscha'I(j-2.10

2.09-2.51

1.73-2.19

~.

masou

I

kisutch1.87-3.60

p - 2 . 2 4

1.69-3.12

2.08-2.15

1I

rhodurus~-

1.48-3.84
2.38-3.96

In the light of the above findings, it is difficult to take such an element as above asa standard to distinguish the species of Oncorhynchus.

Uj

Number of the chromosomes

It is recently that chromosome cytology has made significant contributions to the development of animal systematics.
meaning amd impetus.

Cytological and genetical analyses gave taxonomy a newThus, the mutual understanding between systematists and cyt-

f l a new approach to the concept of species.
ogenetists has enhauced

Cytologists are concernedwith the cyto-taxonomic differences which exists between related species.

They- deal withdifference in chromosome-number or in the sizes and shapes of some of the chromosome
29

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

set.

Such differences are useful to distinguish cryptic species that cannot be separated by

speci mens of merely morpholog-ical characters by non-cytologists. Since all evolutionary ch-Panges have had their origin i he chromosomes as revealed by recent extensive progress ofcytology,. it ;s t-ery valuable o use cytelogical knowledge in establishing the relationship oftaxonomic arrangements by comparing in detail the morphological features of the chromosomes among related species of organisms.

T h e hehavior and morphological changes ofchromosomes in relation to the taxonomical arrangement has become a subject of soundimportance to taxonimists. The Salmonidae is regarded as a group of fishes in which there
occur many difficulties with regards to the d e t 6 i n a t i o n of species.

Recent progress ofcytology has revealed that the differences in number and shape of the chromosomes furnish
basic and important data available for the

distinguishment ofthespecies.

Reference

to the monograph published by blakino (1956) has shown that there are 19 species and4 hybrid salmon in which the chromosome numbers have been reported so far in the
Salmonidae. More recently Nogusa (1960) has contri4uted to this field of research in publishing a monograph of fish chromosomes. According to his study, the chromosome numbersof four species of Oncorhynchzis are determined as follows : masou, r h o d 7 ~ ~and7 ~ kela~areall 50 in haploid number, while nerke is characterized by a haploid number of 54.

However,the chromosomes of gorbuscha, tschawytscha and kisutch have not been studied by any
authors.

The majority of the chromosomes of the Salmonidae is of dot like structure in

outline.

At the present situation, the knowledge of the chromosomes seems not useful forthe identification of species of the Salmonidae, partcularly of those of the genus Oncorhy-nchus.

Part 2.

Difference of external characters between salmon fingerling and adult stages.

As all the pacific salmon are, in general,similar to each other in form and also

in life history, it is difficult to accurately distinguishthe species.

In spite oftheseexternal difficulties, some remarkable features occur in the fingerling and adult stages,presenting a series of parr marks in the former, while in the latter stage, there occur
some drastic changes of head portion and nuptical coloration, properly known as secondary

sexual characters.

T h e adult spawner strongly become much darker in color, bearing various

nuptical blotches on the sides. Further their from the head, strongly curved like hook,developing falcate teeth in front of both jaws. On the other hand, the parr marks, thenumber of blotches or spots, and their distribution in fingerling varied gradually with advanceof body growth : namely the parr marks disappear already in the stream before theirdescending and are covered with silvery color by the guanin on seale, being perfectly adapted
for sea migration, while other spots gradually appear on the body. The color change
in each species will be observed in detail in the latter section. Here, the writer wishes
to deal with a comparison of different characters inearly

parr-stage fingerlings.

The

collecting localities, the total length and rates of some parts of the body are as shownin Tables 11. and 12.
The distinguishable characters were studied in each fingerlings : they described in detailin the following pages.

Oncorhynchus kela - Body form, more slender and lower depth ; parr mark, rather slender30

Ecological and Morphological Studies of the Genus Oncorh~nchus

Table 11. Collecting localities of the species under study.

I

Species

Locality
Chitose hatchery, Chitose river, and Kaisei, qubetsu river.
Port John, coastal British Columbia, Canada.
Shikotsu Lake, and Swelter Creek, Fraser river, Canada.
Chitose river, and Memu stream (Original : Dungeness river, Washington. U. S. A,;.
Memu stream, Tokachi river system, and Nizibetsu hatchery, Nishibetsu river.
Kuril Lake, Bolshaya river, Kamchatka, Russia, and Name Freshwater Fishculture Experimental Stat'on, Hokkaido University.
Nikko Trout Hatchery, Fishery Agency.

keta
gorbuschanerkatschawytschamasoukisutchrhodurus

Table 12. Ranges of some b d y proportions in the fingerlings studied.

__Species

Items
__

1,

kata
gorbuschanerkatschawytschamasoukisutchrhodurus
Land-lockednrrka

Total length (cm.)

1

7.8-9.7
8. 1-8.9
8.7-10.2
7.1-8.1
4.0-6.6

4.46-4.76
4.60-4.94
4.33-4.38
4.44-4.83
4.08-4.16
3.81-4.61

5.0-8.3

1

Tihead5.54-6.60
5.96-7.14
5.56-7.00
4.43-4.84
4.30-5.03
4.37-5.64
5.00-5.74

2.78-3.63
3.30-4.13
3.00-4.25
3.08-3.55
2.60-2.77
2.86-3.20
2.60-3.57.~

6.9-8.3,

4.76-5.56

bars, scarecely extending below lateral line ;back, sometimes from dark to light. However they have many individual variations,distal part of dorsal darkish, but other fins pale in color; ground color, greenish
iridescence on back.

Oncorhynchus gorbuscha - Body form, much slender and lower depth ; parr mark and otherspots completely absent ; dorsal and caudal fins somewhat darkish ; ground color,bluish to darkish blue on back. This species is readily distinguishable from otherspecies.

Ocorhynchus nerka - Body form, slender and lower depth ; parr mark, somewhat oval orrather bars, scarecely extending below lateral line ; black spots, commonly on backin sea-run form, but irregular, comparatively conspicuous in land-locked ; someblack dots under side below lateral line ; all fins pale ; ground color bluish on back.

Oncorhynchus masou - Body form, not slender and higher depth ; parr mark, conspicous,
ellaptical, extending completely across side of body ; other blotches, upwards ofinterspace between parr marks present oval blotches along the dorsal, sometimes
downwards small roundish present ; black spots, scattering along the dorsal ; distalof dorsal blackish, and a anterior margin of anal white, and its inner part blackish
pigments present; the first few anal rays are lengthend; ground color, darkishbrown to lighter by indivdiuals.

Oncorhynchus Risulch - Body form, similar to m a s m ; parr mark somewhat long ellaptical,
extending almost completely across the lateral line : other blotches, upper side of

Scientific Reports of the Hokkaido Salmon Hatchery No. 17parr mark present but indistinct; caudal peduncle rather high ; anterior
part of dorsal somewhat blackish;anterior distal part of anal marginedwith white; orengish tinge on pectoral, ventral and anal fins. This species close resemble to the former
species in ganeral appearance.

Oncorhynchus tschawytscha - Body form, rather similar to former two species, butslightly low depth; parr mark, moreor less elongate ellaptical, almost
completely across the lateral line ofbody ; rather large roundish markings
upwards of interspace between parrmarks ; black spots numerous, conspi-

cous along the back of sides ; anterior
basal part of dorsal jet black, butorange tinge on ventrals, caudal andanal ; caudal peduncle depth rather
low; mouth tip more blunt than theother species ; ground color, dark greenish blue to dark brown on back; thefirst few anal rays not lengthend, unlike in kisutch and masou fingerlings.
Onco~hynchusrhodurus - Body form, rather
similar to masou, but body depth
relatively lower as tschawytscha ; parrmark conspicous, elliptic, extending
almost cempletely across side of body;backwards of interspace between parrmarks oval marking present; otherblack spots scatterand distinct;

on

the

some small

backcrimsondots on anterior part of lateral lineI(about 3 to 4cm. in body length) clearly present; caudal peduncle rather
high; anterior distal part of dorsal
and anal fins margined with white,
and in its inner part black pigment
present ; ground color, darkish brown
32

D

Fig.

5.

I

Cm

3

The external forms in fingerlingsof L-ecies
belonging to genus
Oncorhjnchus :a. Land-locked nerka, b. nerka,
c. keta, d. gorbuscha, e. kisutch,
f . masou, g. tschawytscha.
h. rhodurus

Ecological and Morphological Studies of the Genus Oncorh~nchus
in preserved specimen but in life sooty grayish dark to greenish dark-brown ;orangish tinge in coudal, anal, ventral and pectoral 'fins.
U p to the present time, several important studies concerning the salmon fingerlings
have been made by Foersters and Prichard (1934) on Canadian species, Schultz (1935) on
United States of American species, and Desler (1957) on those in Russia.
Almost all the features of the six species as above mentioned agree in description
with the points presented by the previous authors.
Based on the results of above morphological observations, the species of Oncorhynchus
can apparently by separated into two groups as regard to external characters : one is apparently elongate-lower in form and the other more pudy-higher in general appearance. The
species to be classified into the former group are keta nerka and gor6zrscha, while the latterinclude the following species, masou, kisutch, tschawytscha and rhodurus. Other spots which
occur in adult salmon are gradually apparent mostly with the growth of individuals, though,of course, the appearance of those characters differs in different species.

Of the species,

keta have numerous fine black spots on back of fingerlings, though adult fishes lack tohave such spots.

However, there are often present individuals with minute dots on thebasal part of the dorsal fin or sometimes on back.

T h e fingerlings of nwrka are similar inappearance to those of keta, but the sea-migrant adults generally have on speckles on thebody, though there are often black spots scattering along the back and upper lobe of
caudal fin. Although gur6uscha fingerlings are entirely lacking the parr and other markings,
the adults have always remarkable oval or somewhat elongated black blotches on back,particularly more prominent on caudal fin.

However, there is rarely to be found the ind-ividual without markings as found in the fingerling stage. In adult masou, some small blackpunctuations are scattered, a few being on back and upper part of caudal fin, though thefingerling has in the distinct characters. In addition, the parr marks and black spots conspicously remain the land-locked forms living in the river, while those in lake-dwellers usually covered with guanin and some black spots on back. Also, although the kisutch
fingerlings have numerous brown spots on back, the adults are charcterized by a small
number of these patterns.

The last species, tschawytscha, have not s o much speckles in

the fingerling, but after about one year they begin to arrange throughout back and caudal
fin some markings as found in adult forms of the sea migrants.
In spite of the occurrence in the character as above mentioned in some extent within
species, the evidence to show that all the six species under consideration is divided into

two groups seems to be the most important morphological feature for identification of
species.
Furthermore, the external characters as revealed in salmon fingerlings are not only
mostly available for the identification of the species, as described taxonomically by theprevious authors, but also fdr separating species of each group from the phylogenetic pointof view.

Part 3.

Some ecological and morphological observations on the Pacific salmon, including their distribution.
33

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

In the following, the writer deals with general observations regarding some morphological and ecological features of the pacific salmon including the distribution of the speciesof the genus Oncorhynchus.
Family Salmonidae
Body rather elongate, subfusiform ; Head scaleless ; Mouth large, terminal ; Maxillary
and premaxillary forming lateral margin of upper jaw ; Maxillary long, have a lancelete
supplemental bone, generally extending beyond behind orbit ;Premaxillary not protrude ;Teeth
various, often lacking those of jaws with moderate teeth, especially in mature male enoumously elongate at anteriormost part; Vomer long and narrow flatish with one or two
rows of teeth both an its head and shaft; Palatine with a series of teeth; Gill four, slit

behind the fourth ; Pseudobranchiae present, well developed ; Gill-raker rather numerous ; Gillmembrane free from the isthmus ; Scale small or moderate, cycloid form ; Branchiostegals
rather numerous about 10-20; Dorsal almost median portion, its rays 11-15, only two or
more undeveloped rays in front, the others simple and branched ; Adipose fin present,
fleshy; Caudal fin forked or subtruncate ; Anal fin moderate or rather long ; Ventral abdominal, not large ; Pectorals low7 and moderate ; Lateral line well developed ; Ovum large,
not adhesive ; Air-bladder large and elongate : Stomach siphonic form ; Scaly appendage
almost the base of rentrals ; Intestine comparative short ; Pyloric caeca more numerous ; Allsalmoy almost anadromous, limited to cold and temperate waters of northern hemisphere ;Spawning in freshwater only.
1.

Oncorlzynchus ketu (walbaum)
Total length ranges 36.2-78.7 cm. ; Head 3.6-4.9 in standard ; Body depth 3.6-5.8 ;Caudal peduncle length 9.:+13.2 ; Snout to dorsal I . 9-2.2 ; Snout to pectoral 4.0-5.1 ; Snout
to anal 1.37-1.42;Snout to ventral 1.7-1.9; Snout 2.2-3.8 in head; Fye 3.6-4.9 ; Interorbital width 2.1-2.2;Mouth cleft 1.6-2.0 ; Postorbital 1.6-2.0 ; Longest dorsal 1.5-2.5 ;Idongest pectoral 1.5-2.8 ; Longest anal 1.3-3.5 ; Longest ventral 2. 0-4.6 ; Depth of caudal
peduncle 3.14-3.58 ;Dorsal 11-16 jusualiy 14); Pectoral 14-17 (15); Anal 14-18 (17); Ventral 10-12 (11);Caudal 41-44; Branchiostegals 11-15 (13) ; Vertebrae 62-69 (65-66) ; Pyloric caeca 125-215(160-180) ; Gillrakers 12-16
8-10-21-25(23); Dental range40-42;
21-28 Vomerian teeth 4-8; Palatine teeth
9-10 ; PseudoGranchae 17-20 ; 1,ateral line 132-146 (135-137) ; First row above lateral line
135-153 ; Transverse scale 34-52 ;Body rather elongate, more compressed. Caudal peduncle slender. Caudal emargenate.
Head moderate, conical. Mouth moderate.

Snout rather pointed.

Teeth small and weak

conic at sea migrants, but in mature adult becomes strongly fang-like, particular in male.
Gill-rakers comparative short, slender, widely spaced, in its inner snrface fine spicules absent
or when present with a single row.

Scale deciduous. In fresh color, grayish blue to metelic

blue above, side and below silvery white, back and side with no black spots and othermarkings but occasionally a few- speckling on dorsal base and behind head.
spawning adult wholly blackish above and side with irregular purplish red, black,yellowish, mottled streaks or bars which is known as “Buna” in Japanese. White on tips
34

Ecological and Morphological Studies of the Genus Oncorhynchus

of ventral, anal and lower margin of caudal

Generally very close to nerka, especially in oceanic migrants, but readily distinguishable
by some radial silver stripes on the basal part of the caudal fin, also separates by absenceof black spots on back, fin, and more slender caudal peduncle.
This species shows very rarely abnormal individuals which are remarkable by larger
scales, mottled coloration on body and pug-head (Hikita 1955, 1958, Sano 1958). In Hokkaido,
there were found two races in this salmon, one is the feeding school, migrating mainly toPacific coast during warm summer seasons, while another one includes the spawning migrants
which enter into streams to spawn from September to December in every fall season.
T h e former is called as “Tokishirazu” in various places of Hokkaido, while the latter are
known by proper persons as “Aki-sake” or “Aki-zake”, respectively. It is practically impossible to separate the Tokishirazu race briefly by means ef external characters from thespawning ones. However, if the specimens be observed in detail, the summer race are recognizable morphologically by imperceptible difference in number of the pyloric caeca, since theformer have more larger number than the latter, and no spicules occur on the rakers. The
catch of the spawning race from coasts and streams of Hokkaido are much more thanthat of the summer migrants.
The number of eggs is mature females is different by individuals, body length, localities orTable 13. Mature egg-number of 0. keta from several localities in
Hokkaido (after Sakano and Miura‘s unpublished data)
River name

I Tot;L&ygtl
I

Yurappu
Shiriuchi
Yufutsu

TokoroTokachi

~~

-

~~

left

right

Total

Average

1.488
1.461-1.838
1.582-2.205
2.057
1.346
1. 115-2.124
1.836-2.340
949-1.352
1.503-1.861
1.375-2.081

1.560
1.485-2.004
1.483-2.175
2.064
1.355
1.127-2.454
1.859-2.464
885-1.272
1.522-1.795
1.441-1.991

3.048
2.941-3.762
2.962-4.384
4.121
2.701
2.082-4.834
1.948-4.839
1.842-2.600
3.025-3.565
2.816-4.072

--__

,

67.0
71.0-78.0
62.5-69.0
72.0
57.0
61.0-69.8
70.0-75.8
52.0-58.4
60.0-64.5
61.1-69.4

3.352
3.650
-_--

--_-

3.530
3.997
2.309
3.320
3.238
~

returning age. Of course, the appearance of some morphological charact~-

s such as age

composition and egg-number fluctuated with considerable ranges by river or by year.
Recently, the articial propagation of this species has extensively been carried out in Japan,
chiefly in Hokkaido and Tohoku districts for the maintenance and rehabilitation of declining
populations

This species seems to require three to six years for maturity.

Local name-Aki-sake, Aki-zake, Tokishirazu (Hokkaido) ; Shiro-sake, Shiro (North Pacific
Ocean, Kuril Islands and Kamchatka); Shyake (Kanto Districts); Ohsuke (southern Hokkaido);

Bum, Bunake, Pinko, Mezika (Hokkaido) ; Ohme and Ohmanako (Miyagi Prefecture); Inu-masu(Ishikari Province, Miyagi Prefecture) ; Hanamagari (Iwate Prefecture and Hokkaido) ;Foreign name-Chum salmon, Dog salmon, Calico salmon, Hayko, Lekei salmon, Keta,
35

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

Letenaya keta, Osenniyaya keta.
Geographical range-This species is most widely distributed throughout the northernwaters of Pacific Ocean and Bering Sea, ranging southward to Japan in eastern Asia sideand to California in North America. In Japan, it also extends south to northern Kyushu
in Japan Sea coast and in pacific shoreline to Tone river, Kanto District. Along the arctic
drainage, this species is found in the majority of areas from Lena river of eastern Siberia to
Mackenzie river in Canada.

2.

Oncorhynchus gorbuscha (Walbaum)
Total length ranges 40.2-67.5cm. ; Head 3.0-5.8 in standard ; Body depth 3.1-5.0 ;Caudal peduncle length 8.8-16.8 ; Snout to dorsal 1.9-2.2 ; Snout to pectoral 3.5-5.5 ;Snout to anal 1.40-1.49 ; Snout to ventral 1.6-2.0 ; Snout 2.1-3.8 in head; Eye 7.85-10.8 ;Interorbital width 2.0-3.6 ; Mouth cleft 1.8-2.7 ; Postorbital 1.2-2.2 ; Longest dorsal
1.5-2.8 ; Longest pectoral 1.3-2.2 ; Longest anal 1.8-3.5 ; Longest ventral 1.6-3.0 ;Depthof caudal peduncle 3.21-4.15 ;Dorsal 12-18 (usuallyl5) ; Pectoral 13-17(15) ; Anal 16-19(18) ; Ventral 11-12(11) ; Caudal
40-45 ; Branchiostegals 11-14 (12) ; Vertebrae 67-70 (68) ; Pyloric caeca 91-188 (126) ; Gill10-15

rakers-26-33
16-22(31) ; Dental range-; 25-27

Vomerian teeth 7-10 ; Palatine teeth 6-12 ; Pse-udobranchiae 21-25 ; Lateral line 127-204 (178) ; First row above lateral line 131-230 ; Transverse scale 53-74 ;Body small, rather slender, somewhat compressed. Caudal peduncle slender.
emargnate or subtruncate.

CaudalHead moderate, conical in both sexes of sea migrants. In

mature female comparative plump and not transform, but in male thin, compressed, withsharp curved back, protuberance much developed and jaws extremely prolonged, but not somuch strong in female. Snout rather sharply pointed.

Mouth moderate.

Teeth small,weak, and these on the anterior part considerable developed in mature male. Scale smaller
and numerous, and easiest deciduous. Gill-rakers slender, with minute spicules of single
or two rows and its number numerous, longest gill-raker about 1 . 3 cm. in length. In fresh,
color bluish or greenish blue above side silvery. Blotches numerous, large, more or lessoval or sometimes ting-like on back, those on the caudal fin pecularly conspicuous, large
and oblong in shape. No markings on head. The spawning male grayish blue above, blackand yellowish white blotched on side. White on distal parts of caudal and flap margin of
the gill-cover.
This species is separated from other species by the small scale, great number of gillrakers and distinctive large black blotches on back and caudal fin.
prominent feature with a humpback behind head portion.

It has also the most

It is formed by an accumulationof connective tissues and fatty substance to the parts between muscle levator pinne dorsalis
and hypoderm. The number of mature roe based on the species collected from several
localities shows range differences as indicated in Table 14.
T h e pink salmon, gorduscha, is more common along the coasts of Okhotsk Sea and
Nemuro Strait. Tha spawning of this salmon takes place from late August to late September in Hokkaido.

It is caught abundantly in Hokkaido every year. The artificial propa36

Ecological and Morphological Studies of the Genus Oncorhynchus
Tablr 14. The egg number ranges of both side of ovaries based on specimens from several
localities in Hokkaido ( after Sakano and Miura's unpublished data).

River nameShibetsu
Yube ts u
TokoroTokus hi betsu

I ForFc2.ygth
44.0-48.0
50.0-54.0
48.5-49.6
50.0-53.0
45.0-47.0
51.0-55.0
48.0

Total
668-946985-1.260
713-1.441
825-956796-806
747-887866

935-913943-1.201
804-1.475
843-1.205
637-726686-1.003
85 1

1.330-1.775
1.928-2.46 1
1.517-2.916
1.668-2.099
1.477-1.532
1.477-2.000
1.717

1

Average
1.564
2.152
1.956
1': 89 1
1.483
1.711

_-_

gation has been carried out in hatcheries which located in several parts of Hokkaido, fortheir conservation and maintenance. Recently the planting and marking experiments of thisspecies are actively practising in several places of Hokkaido and Tohoku districts, because ofreaching to mature age is shorter years than other species. The maturity of this species seems
to complete in almost two or rarely three years.
Local name-Karafuto-masu, Seppari-masu (Hokkaido in proper) ; Seigo-masu (Akkeshi

and Kushiro Province) ; Ao-masu (Hamanaka and southern Hokkaido) ; Masu (North Pacific
Ocean and southern Hokkaido) ; Kan-masu (Muroran District) ; Yaichippu, Rakuda-masu,
A-masu (Kesen-numa);
Foreign name-Pink salmon, Humpback salmon, Haddo, Halia, Last salmon, Hone salmon, Dog salmon (rare in Alaska), Gorbuscha (Russia), Pukkellaks (Norway).
Geographical range-The pink salmon is a common species in Hokkaido, and reaches
northward to the Arctic Ocean. The distribution are Kuril Islands, Amur river, Okhotsk
Sea, west to Lena river on eastern Asia and east to Mackenzie river system in Canada.
I n American coast, the distribution is usually extended from Alaska to California. North
Pacific Ocean and Bering Sea is most common locality.
3. Oncorhynchus masou (Brevoort)
Total length ranges 17.9-57. Ocm. ; Head 3.5-4.6 in standard ; Body depth 3.4-4.7 ;Caudal peduncle length 8.2-13.7 ; Snout to dorsal 1.8-2.4 ; Snout to pectoral 3.9-5.4 ;Snout to anal 1.2-1.5; Snout to ventral 1.1-1.9; Snout 2.7-3.8 in head; Eye 3.2-11.7;
Interorbital width 2.3-4.3 ; Mouth cleft 2 . 3 - 3 . 2 ; Postorbital 1.7-2.2 ; Longest dorsal 1.62 . 1 ; Longest pectoral 1.49-1.90 ; Longest anal 1.5-2.6 ; Longest ventral 1.8-2.3 ; Depthof caudal peduncle 2.56-3.04 ;Dorsal 13-18 (usually 14); Pectoral 12-17 (14); Anal 13-18 (16); Ventral 9-11 (mostly10) ; Caudal 45-47 ; Branchiostegals 11-14 (13); Vertebrae 63-69 (6465); Pyloric caeca 356-9
5-9
68 (ca. 50);Gill rakers m 1 6 - 2 2 (18-19), land-locked f 0 r m - ~ ~ 1 4 - 2 (17-19)
1; Dental range- 24-25
38-42 ; Vomerian teeth 6-17 ; Palatine teeth 8-12 ; Pseudobranchiae 13-19 ; Lateral line
120-140(123) ;First row above lateral line 121-141 ; Transverse scale 43-56 ;Body moderate elongate, somewhat compressed. Caudal peduncle stout ; Caudal emarginate. Head conical. Snout slight blunt. Mouth moderate. Teeth small. Gill-rakers
shorter triangular, widely spaced, with two spicule rows and the longest raker 5 mm. in37

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

1

Shyari

Shibetsu
Tokushibetsu-~~~

44.5-49.5
51.5-52.0
44.0-49.5
52.0-50.5
44.6-49.8

1

791-1.355
1.292-1.373
1.026-1.634
1.612-1.652
1.114-1.443I723-1.091
1.011-1.138
912-1.391
1.025-1.300
748-1.383
~~

38

~.

1.569-1.081
2.389-2.430
1.932-2.879
2.858-2.912
1.987-2.698
~____

1.975
2.410
2.549
2.885
2.402

Ecological and Morphological Studies of the Genus Oncorkyzckus

Yanagippa ; Shoma, Shima (Kamchatka and southern Sxghalin) ; Ichyanui (in Aino) ;Land-locked form : Enoha (Kyushu) ; Gin-enoha, Suginoko, Yamabe, Yamame, Ginkeyamabe (Hokkaido) ; Yamabai, Yome, Yamo, Kurosobu, Karasu-masu or Kuro-masu (LakeToya) ; Towada-masu or Kawa-masu (Lake Towada) ;Foreign name-Masou

salmon, Masu salmon, Japanese salmon, Salmon trout, Cherrysalmon, Mazi, Shima (Russia.)
Geographical range-This species is a native to Japan and adjacent waters, and occuresouthward to northern Kyushu, but is most common in riijrthern Honshiu, especially in
Hokkaido.

It is the Daikokei river of Formosa where &e present species was firstly

described as Oncorhynchus formosanus by Oshima and Jordan (1919). Other localities so
far known are eastern Korea, Great Peter's Bay, Amur river, Usury Bay, Maritinie Province
and western Kamchatka coast in Russia.
Specimens which were described by Jordan and McGregor (1925) as a new species,
0. ishikawao, from many localities are nearly agreeable in several characters with thew t e r ' s results as given in the following table, and therefore the present writer wishes totreat t k species as a synonym of landlocked form of the masou salmon; 0. masou.
~~~

~

~~

Items

Original
Present count

1

I

_

_

~

I
~~

A.

B.

______-

1

12-13
13-17

11-14

11-14

1

1

~

P. c.
37-58
'

42-47

Note- A : Anal. B : Branchiostegals.
\7 : Vertebrae.

-.r I
I V . 7 1

G.

63-69

18-21

63-65

14-19

I

1

L. lat.
125-1 40

117-138

P. C. : Pyloric caeca

G : Gill-rakers. L.lat. : Lateral line.

4. Oncorhynchus tsehawytscha (Walbaum)
Total length ranges 33.6-96.2cm. ; Head 3.8-4.3 in standard ; Body depth 3.3-4.3 ;Caudal peduncle length 8.2-13.8 ; Snout to dorsal 2.1-2.3 ; Snout to pectoral 4.1-5.0 ;Snout to anal 1.40-1.45 ; Snout to ventral 1.8-1.9 ;Snout 2 . 3 - 3 . 4 in head ; Eye 7.3-13.7;
Interorbital width 2.4-3. 2 ; Mouth cleft 2. 7-3. 1; Postorbital 1. 2-2. 8 ; Longest dorsal
2.0-2.8 ; Longest pectoral 1.6-1.9 ; Longest anal 2.6-4.3 ; Longest ventral 2.0-2.4 ; Depthof caudal peduncle 2.91-3.31 ;Dorsal 14-17 (usually 15); Pectoral 15-19 (17) ; Anal 17-20 (19) ; Ventral 10-13 (11);Caudal 3 - 4 0 ; Branchiostegals 16-19 (17) ; Vertebrae 71-72 ; Pyloric caeca 127-170 (153);
8-11
Gill-rakers --20-2:3(21); Denial range41-44; Vomerian teeth 3 ; Palatine teeth 11-17 ;11-13
23
Pseudobranchae 15-17 ; Lateral line 129-152 (147) ; First row above lateral line 137-160 ;Transverse scale 50-53 ;Body rather elongate, rabust, somewhat compressed.

Caudal peduncle comparative

slender. Caudal forked. Head moderate, conical. Snout blunt. Mouth moderate. Eye small.
Teeth small, not strong, conical shape, longer on side of lower jaw than anterior part.
Maxillary stout, its posterior slightly curved, falcate shape. Gill-raker is rather slenderwith two rows spicules long inner side, longest raker 1.3cm. in length. Scale deciduous.
Coloration at sea, dusky or blackish above, side and below silvery. Head dark slaty and39

Scientific Reports of the Hokkaido Salmon Hatchery No. 17
its anterior black, more darker than body.

Numerous, roundish black spots on back, a few

dorsal and caudal fins. In mature adult, especially in male more blackish with dull reddish
blotches often on side. Pectoral, ventral and anal white, but sometimes dusky. Branchioste
gals blackish. No spots on a adipose fin. Mouth cavity and gums darker or blackish.
This species are remarkable by blunter snout, the greater number of pyloric caeca,
small eye, blackish coloration in general appearance, and black spots on back, dorsal andcaudal fin.
T h e chinook salmon, tschawytscha, is of the largest form in the spesies among O ~ C O ~hynchus. They migrate in small number
along coasts around Hokkaido, every year,
particular along the Pacific coast.

There-

fore, there is no detailed report concerning
the spawning of this species in. Japan. The
chinook which is remarkable by more orless marked secondary sexual characters hashitherto been caught in several rivers of
Hokkaido.

T h e collecting places of thisspecies were shown by the present writer as
indicated in the following map.
I n all probability, the spawning of thisspecies may occur in certain suitable rivers
in Hokkaido.

Based on the expectation,these eyed eggs were transplanted throughthe courtesy of the Washington Departmentof Fisheries in 1959, 1960,

1961 and 1962

V
Figure 6.

A map indicating several ascending
rivers of' the chinook salmon :1. Teshio 2. Yubetsu 3. Tokoro
4. Shyari 5. Oboro 6. Tokachi

for the esterblishment of a new habitat, and released aggressively a number of fingerlingsin the Tokachi river.
Local name-Masunosuke, Suke (Akkeshi Province, Kamchatka, Kuril Islands and North
Pacific Ocean) ; Satsu kei (Kamchatka) ; Itou-masu, Iuo-masu, Ohsuke (Shiogama, Miyagi
Prefecture, Kushiro and Akkeshi Provinces) ;Foreign name-King salmon, Chinook salmon, Quinnat salmon, Columbia river salmon,
Sacramento river salmon, Tyee salmon, Spring salmon, Fall salmon, Black salmon, Hookbill,
Black mouth, Chub salmon, Chauicha (Russia), SalmBn rey, Salm6n real, SalmBn deCalifornia (Chile).
Geographical range-The king salmon extends from northern Japan, Amur river, Okhotsk
Sea to Anadir of Chuktchi Peninsula on eastern Asia side and from southern California
to northwestern Alaska on American side. Also, it is common observed throughout North
Pacific Ocean and Bering Sea.

5.

Oncorhynchus nerka(Wa1baum)
Total length ranges 12.2-66.5cm. ; Head 3.8-4.7 in standard ; Body depth 3.2-4.1 ;Caudal peduncle length 7.7-12.0 ; Snout to dorsal 2.0-2.5 ; Snout to pectoral 4.1-6.1 ;Ecological and Morphological Studies of the Genus Oncorhynchus
Snout to anal 1.3-1.49; Snout to ventral 1.8-2.1; Snout 2.7-3.9 in head; Eye 5.3-8.8;
Interorbital width 2.5-3.1 ; Mouth cleft 2.5-3.6 ; Postorbital 1.6-2.0 ; Longest dorsal 1.7-

2 . 5 ; Longest pectoral 1.3-1.8 ; Longest anal 2.0-2.9 ; Longest ventral 1.7-2.7 ; Depth of
caudal peduncle 2.52-3.21 ;(usually 14 or 15) ; Pectoral 15-18 (15) ; Anal 15-19

Dorsal 12-17

11- 12 (11) ; Caudal(18) ; Ventral

45 - 47 ; Branchiostegals 11-15 (13- 14) ; Vertebrae 66 - 69 (67) ;Pyloric c'aeca 80-117 (91) ; land-locked form 67 - 94 (83) ; Gill-rakers -73-39(35-36),
18-24
9 -15
38-40
34-35
land-locked form-27-38(31-34) ; Dental range-,land-locked form; Vomerian
17-24

22

20-21

teeth 6-9 ; land-locked form 6-8 ; Palatine teeth 8-12 ; Pseudobranchiae 15-21 ; Lateral line
130-140 (133) ; First row above lateral line 137-141 ; Transverse scale 37-46 ;Body elongate, rather slender, compressed. Caudal peduncle somewhat stout. Caudal
deep emarginate.

Head short, rather shape conic.

Snout pointed.

Mouth moderate.

Teeth

extreme small. Eye large. Maxillary rather narrow, its posterior end pointed. Gill-rakers
long, slender, thick close set, with two or three minute spicule rows, and longest raker
1.2cm. in length; Flesh deep red. Scale rather large, not deciduous. Anal low. Adipose
fin small, slightly larger in male than female. At sea, color greenish blue to dark blue
above, side silvery
black.

No spots in usual, but rarely minute speckling above. Caudal fin-

Lower fins pale. In mature adult, male extreme hooked snout, humpback.

Color

in mature male, body, adipose, anal and ventral uniformly pretty blood red, excepting
head portion. Pectoral and ventral dull red, greenish dark blue on head, caudal yellowish
with black spots or absence, sidegreenish blue. In land-locked form, bluish dark-backand belly silvery white on both sex. Mature malecaudal peduncle excepting on head and caudal.

reddish on body, especially on

Dorsal, ventral and pectoral blackish,caudal and head yellowish or light olivacious with obscure black spots, in turn, femalecaudal slight reddish but side and back dusky, with on lateral line dark blotches. Headportion dark greenish on top, side more or less dull silvery.
Paired and vertical fins dark.

Anterior part of ventral side white.

T h e abnormality ofthis species has been hitherto observed in some pug-head (Sano, 1958) and larger scale
individuals (Hikits's unpublished) from North Pacific Ocean.
A sample of a spawning form was once obtained in the Shibetsu river of the easternregion of Hokkaido. T h e land-locked kokanee is well known to anglers and many persons
with Japanese name of ~~~~~~-masu" that was nominated by Mr. Moriwaki, Director of
the Hokkaido Fisheries Experimental Station, owing to its beautiful dwarf fish-form.
Considering from the fact on their transplantation in Hokkaido, Lake Shikotsu was theoriginal center of the kokanee stock. So far as the writer is aware, they have for merely
been planted from this lake into several lakes and ponds such as Ohnuma, Uryu, Panke,
Kuttara and Toya. Among them, Ohnuma was unsuccessful in transplantaion and the statusof Uryu is still unknown at present. T h e lakes in which the land-locked kokanee inhabits atpresent are as shown in Figure 7 .
T h e general form and proportions of the body, especially those of head portion andcaudal depth, of the land-locked kokanee salmon are considerably different according to
the lakes they lived.
41

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

The mature age of this species in different lakes, the average being approximately three years in male and four
years in females. T h e average numberof mature eggs as observed in the Towada lake in 644, being 290 in right and

250 in left side. The range based on
21 samples is 442 to 879. T h e body
varies from 28.8 to 34.5 in total length.
Furthermore, the gill-rakers of this species are closely set on branchial arches,and so they are chiefly suitable to takeplanktonic organisms as food.

Figure 7.

Artificial hatching of this species

has been undertaken in order to maintain the resource.

The eggs have acti-

vely been transplanting to many lakes

Distribution of the land-locked kokanee
salmon Oncorhynchus nerka, within
Hok kaido.
1. Toya 2. Kuttara 3. Shikotsu
4. Uryu 5. Chimikeppu 6. Akan
7. Panke
Shibetsu riverof Hokkaido and the Hondo.

A specimen obtained in Lake Hakone in October 1922 was described by Jordan and
McGregor (1925) as a new species, Oncorhynchus adonis. Some external characters examinedby the writer are not in agreement with their original description.

,

Therefore, the writer

wishes to treat this species as a land-locked kokanee salmon, being synonym to 0. nerka.
For reference, are shown in the following the counts in the original description.
Items
Originalcounts

I *. I

A.

10

13

~

~

/ P . c.
67-69

I

I

V.
66

I

I

G.
31-33

1 ~ . 1 a t /V 0 r m . t .

I

131-134I

5This species can be identified based on a greater number of gill-rakers, and a small
number of pyloric caeca.

In fresh samples, they are clearly distinguishable by jet blackon caudal in the open sea; in mature specimens by humpback and blood red in bodycoloration except head portion and caudal fin.

Moreover, land-locked forms are clearly

separated by their fine specklings on the body and caudal fin, and as well as by thewhole red color, somewhat dusky.
Local name-Beni-sake, Beni-masu, Beni-zake, Ekni (Kamchatka, northern Kurd Islands
and North Pacific Ocean) ; Akazake, Karetchah ;Land-locked form:Hime-masu (Lakes and marshes in Hokkaido and mainland in Japan) ;Kabacheppu, Chippu (in Aino).
Foreign name-Blueback salmon (Canada), Red fish, Red salmon, Freser river salmon,
Sockeye salmon (America), Rid (Alaska), Krasnaya ryba, Nerka (Kussia), SalmBn roji
(Chile), Land-locked form - - - Kokanee, Kokanee salmon, Little red fish.
Geographical range-The sockeye salmon are ranged in distribution from northern parts
42

Ecological and Morphological Studies of the Genus Oncorhpzchusof Hokkaido, Okhotsk Sea, Maritime Province, Kuril Islands; Kamchatka, Komandrsky

Island to Anadir of Chuktchi Peninsula on the Asia side, and from California to northeastern Alaska on American side. They are very common in the Bering Sea and the North
Pacific Ocean.

6.

Oncorhynchus kisutch (Walbaum)
Total length ranges 53.3-64.2cm. ; Head 3.0-4.4 in standard ; Body depth 3.4-3.9 ; Caudal

peduncle lenght 9.7-14.0; Snout to dorsal 2.0-2.2 ; Snout to pectoral 3.2-5.6 ; Snout to anal
; Interorbital width
1.3-1.9 ; Snout to ventral 1.4-1.9 ; Snout 2.6-3.6 in head ; Eye

2.4-2.7 ; Mouth cleft 2.6-3.6 ; Postorbital 1.6-1.9 ; Longest dorsal 2.0-2.4 ; Longest pectoral
1.7-2.0 ; Longest anal 2.0-3.3 ; Longest ventral 2.1-2.5; Depth of caudal peduncle 3.06-3.07 ;Dorsal 13-15 (usually 13); Pectoral 13-16 ; Anal 15-18 (18); Ventral 10-11 (11); Caudal
45-47 ; Branchiostegals 12-14 (13); Vertedsae 67-68 (67); Pyloric caeca 40-80 (63); Gill-rakers'-lo 19-23 (21-22) ; Dental range 21-26 . Vomerian teeth 4 ; Palatine teeth 10-12 ; Pseudo11-14
17-18 '
branchiae 21-29 ; Lateral line 137-146 ; Transverse scale 41-55 ;~~Body rather elongate or oblong, somewhat compressed.
Caudal shallow emarginate or truncate.

Caudal peduncle rather stout.

Head short, conical.

Snout more or less blunt

and its tip slightly curved. Mouth moderate. Maxillary narrow, slender. Teeth small
and needle shape. Gill-rakers rather, stout, roughly wide spaced, with two series of prominent spicules, longest raker 1.1 cm. in length. Scale deciduous. Eye moderate. Interorbital u7idth hroad and evenly convex. Crown of gum white, hroader of gums and balanceof mouth cavity darker.

At sea, color metalic blue or greenish blue, silvery white on sideand belly, irregular black spots on back and upper lobe of caudal fin.
Mature male mostly brick red and mature female a dull brozen. Also broad radialsilvery strips on caudal base. Mature malesnout strongly elongate and downward
curved with comparative small teeth. Dorsal, caudal, adipose darker, and anal andpectoral light dusky.
This species is readily distinguishable
by black spots on back and upper caudal
f i n , small needle-like firmly set teeth, ro-ughly wide spaced gill-rakers and the small number of pyloric caeca, and the stoutcaudal peduncle.

This species has formerly been reported from certain localities in Hokkaido by

Figure 8.

Okada (19:F~)and the present writer (1954).
More recently the writer found a specimen of the migrating form in the Rausu
coast, Shiretoko Peninsula: this specimen
43

A map showing several ascending
rivers of the silver salmon, 0. kisutchin Hokkaido.
1. Yurappu 2. Toshibetsu
3. Shokotsu 4. Horobetsu
5. Horonai

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

was in coloration bright greenish light blue above and silvery with luster on side and belly,with a few conspicuous dark spots on back and upper lobe of the caudal fin. It has silver
coloration on the basal part of the caudal fin.

Collecting rivers so far reported in Hokk-

aido are shown in Figure 8.
Also the writer bas obtained several samples which ascend to the Yurappu river tospawn during November. It has become clear to the writer this salmon enters in a small
number into this river every year. However, the fishing catch of this species in Hokkaido
is very low at present.

Local name-Gin-sake,

Gin-masu, Gin (Nemuro and Akkeshi

Provinces, and North

Pacific Ocean and Bering Sea); Keizi (North Kurile Islands and Kamchatka);
Foreign name-Silver

salmon, Coho salmon, Coho, Medium red salmon, Hookbill,

Hoopid salmon, Silversides, White salmon, Dog salmon, Jack salmon, Quisutch, Kizhych,
Skowitz (Russia), Bielay ryba (Russia), White fish (Kamchatka), Salm6n plateado (Chile).
Geographical range-The

silver salmon is widely distributed from Hokkaido, Kuril

Islands, Kamchatka to Anadir in Chuktchi Peninsula on eastern Siberia, and from northern
California to Alaska on American side, They have commonly been caught in the Bering
Sea and the North Pacific Ocean.

7.

Oncorhynchus rhodurus Jordan and McGregor
cm. ; Head 3.5-4.8in standard ; Body depth 4.1-5.1 ;Total length ranges 16.2-56.8

Caudal peduncle length 2.4-11.3 ; Snout to dorsal 2.1-2.2 ; Snout to pectoral 4.4-5.2 ; Snout
to anal 1.4-1.8; Snout to ventral 1.4-2.0; Snout 2.9-3.6 in head; Eye 3.9-8.0; Interorbital
width 3.0-3.6 ; Mouth cleft 2.1-3.3 ; Postorbital 1.7-2.2 ; Longest dorsal 1.6-2.1 ; Longest
pectoral 1.4-1.9 ; Longest anal 1.4-2.8 ; Longest ventral 1.9-2.5; Depth of caudal peduncle
2.36-3.25 ;Dorsal 12-17 (usually 15); Pectoral 13-17 (15); Anal 13-17 (16); Ventral 10-12 (11);Caudal 38-42 ; Branchiostegals 11-13 (13); Vertebrae 65-66 ; pyloric caeca 45-70 ; Gill-rakers
5 p ~7 17-20

10-12( 2 0 ) ; Dental range- 30-32 . Vomerian teeth 6-8 ; Palatine teeth 12-16 ; Pseudob16-18 ’ranchiae 13-21 ; Lateral line 119-137 ; First row above lateral line 132-145 ; Transverse
scale 40-47;
Body elongate, compressed.
Caudal emarginate or truncate.
Teeth relative small.

Caudal peduncle rather slender.
Head moderate, conical.

Body depth not high.

Snout short, blunt in front.

Gill-rakers short, broad, widely spaced, with two rows spicules but

a few number, and longest raker 7 m m . in length. T h e large mature specimens examined
are ranged from 44.9 to 48.2cm. in total length from Lake Biwa, and they shows thefollowing characters ; in male, body more elongate, compressed.

Jaw much hooked. The

lower jaw perfectly includes to the upper one. Head rather small. Caudal truncate. Eye
Teeth comparative small, its a few large in front. Color; head blackish withmoderate.

some black spots, grayish dark or dark brown on back. Numerous obvious black spots
on back, dorsal, adipose and caudal.

Pectoral, ventral and anal dark and anterior tip ofanal fin white. Sides with reddish and dark brown bars or streaks. Belly white. In small
44

Ecological and Morphologicai Studies of the Genus Oncouhynchus

specimens ranged 28.1 to 31.1 in total length.

Body elongate, compressed.

Caudal peduncle

slender. Head moderate, conical and pointed in front. Eye moderate. Caudal deep forked.
Teeth small. Interorbital width convex.

Body dark slaty above with numerous blackspots. Sides streaks with light gray and pinkish.

Head dark blackish.

Maxillary narrow and its edge blunt or roundish.

apex white.

Ventral and anal

T h e form of a specimen

from Kamihara river in northern Kyushu is 16.2cm. in total length, and its characters are
as follow-Body moderately elongate, much compressed.

forked.

Body depth high.

specimen dark brown above.

Head moderate.

Caudal peduncle stout. Caudal

Eye rather large.

Side and below faint to lighter.

T h e color in preserved
Parr marks oval shaped,

purplish and prominent along the lateral line and nine to ten in number, a few ventral
side below lateral line.
to caudal base.

Numerous small brown spots scattered on back from behind head

Small crimson red spots on side, chiefly above and below lateral line.
First a few anal rays lengthend.

The tips of ventral

and anal fins milky white, while posterior caudal margin blackish.

Head a few dusky

All fins pale without black spots.

blotches present. In 1962, the ten thousand eggs of this species was transplanted from
Lake Chyuzenji into the Chitose Salmon Hatchery, for some culture experiments.
This species is distinguished by more elongate form, the presence of prominent blackspots on back and dorsal fin, a small number of pyloric caeca, short gill-rakers in the lakedweller, and small crimson spots on and around the lateral line in the river-forms.
T h e river and young forms bearing parr marks and crimson specklings are commonly
called “Amago” in Hondo. This dwarf fish closely resemble land-locked forms of themasou salmon, except having small crimson spots. T h e difference between lake and riverresidents is observed as distinct species in general appearance, the former have elongate
form, no parr mark and small black spots, while the latter is higher depth, parr markspresent and peculiar red spots. T h e spawning season in Lake Biwa is late October toNovember every year.
This species was described as 0. macrostomus by Jordan and McGregor (1925) fromseveral lakes and rivers. They gave the counts of several characters which wholly coincidewith the writer‘s ones. Accordingly, the writer whishes to with this species as a synonymof river-dweller or juvenile form of 0. rhodu~us.
--~

1
I

~

~

Items
Original

A.
12-13

__-~

I
1

B.
11-14

~

1

P.

c.

40-61

I 2. I

G.

63-66

17-20

I

I

L. lat.
122-132-

Local name-Enoha, Kin-enoha (Kyushu) ; Ame (Lake Suwa) ; Amago, Amego (southern
mainland in Japan) ; Ameno-uo, Chyuzenji masu, Biwa-masu (Lake Biwa, Chyuzenji, Ashin-oko) ; Hirabe, Hirame (Chyugoku District) ; Kawa-masu (Kiso river) ;Geographical range-This is native to Japan, exclusive in Hokkaido and northern partsof Honshu.

Almost all live only in freshwater but sometimes descends to close to themouth of the river.
This species occurs in many streams and lakes which locate in Hakone, Inland sea,
Kinki, Shikoku and northern Kyushu.
45

Scientific Reports of the Hokkaido Salmon Hatchery- No. 17

Oncorhynchus kawumurue Jordan and McGregor

8.

The writer examined two old preserved specimens of this species obtained in Lake
Tazawa, Akita Prefecture, in the Taisho Era.

They were characterized by the following

measurements :Standard length range 24.5 and 27.0cm. ; Head 3.33 in male, 4.02 in female in standard ;Body depth 3.75, 4.50; Eye 5.20, 4.78 in head; Snout 2.78, 3.72; Interorbital width 3.90,
3.35; Mouth cleft 2.22, 2.57; Dorsal 12-13; Pectoral 1 5 ; Anal 15-17; Ventral 10; Branchiostegals 11-13 ; Gill-rakers17-1633-42 ; Vertedrae 66-67 ; Pyloric caeca 51-54 ; Lateral line
20-26
130-138 ; Transverse scale 39-41 ;Head conical. Snout rather acute angle, rather short.

Maxillary reaching almost to

below postorbital rim. No humpback in mature adult. Color, generally nearly black or
dark blue on back, slightly faint to the side. No dark or blackish spots on body and finsAll fins dusky.
According to the Tazawa Lake Investigation Reports (1915), this species had inhabited
before the Horeki Era (1751-1764), especially during a period from An-nei (1772-1781) toTenmei Eras (1781-1789) they werc most abundantly caught by fishermen on lake coast.
The Japanese name, Kunimasu was named to this fish in the Horeki Era. The reports
state that the fishes seem to live at great depth as inactive swimmer, and feed minuteorganisms or algae growing up on the rock in the bottom. Nearly a decade later, Jordan
and McGregor (1925) described this salmon as a new species, Oncorhynchus kazuarnurut.
Several characters recorded in thcir original description are as shown in the following
table.
-

~

Items
-.

~

I

Original
Rep. Akita Fish. St.

D.

~

11
~

14

~-~~

--

I

I

*.

1 :l

~

B.

-

I
~~

P.c.
_

11-12

51-59

13

47 ?

_

I1-

~

G.

40-4 132

In reference to the original description, the writer found a difference which is represented by the small number of pyloric caeca, while land-locked nerka have a greater numberof pyloric caeca such as 72-94.

Therefore, this species would be regarded as a distinct

species from the sockeye salmon. T h e catch of this species and decreased in the hileiji Era,
and the land-locked nerka occurring in Towada and other lakes were planted into thislake during from 1910 to 1912, for the porpose of maintaining population in this lake.
Since then, these two species inhabit together in this lake.

Several transplantations havebeen made of land-locked nerka into the lake, because of gradual decrease in number bycatch.

But, recently, this species is mostly absent in this lake.

As a result of severaltransplantations, this species may assumably be replaced by the land-locked blueback,Hime-masu, and on this basis the name Kuni-masu seems to use by many people for landlocked nerka at present. T h e writer reputes, therefore, that Kuni-masu is now nearly
extinct or interbreeding with Hime-masu in the lake for a long time.
This species is distinguishable from other salmon mainly by the black color, the46

Ecological and Morphological Studies of the Genus Oncorh3nchus
lacking of black spots, smaller number of pyloric caeca and the greatest number of gillraker.

Part 4.

Interspecific relationships of the Pacifie salmon with some phylogeneticalconsiderations.

It has generally been accepted by the number of paleontological and taxonomi,c studies
that the salmonid fishes had appeared during more recent geological periods. With regard
to its origin, Macfarlane (1923) stated that the salmonid fishes might have evolved froman ancestry of certain freshwater clupaeoid in the Miocene periods, and that their genera
gradually separated from the ancestor and differentiated during the subsequent time.
However, fossil remains of the salmon family is very few in occurrence throughout theworld, though there have been reported of teleostean fossiI fishes.

Regarding the fossilsof salmon relatives, Jordan (1925) stated that some fragments of mature jaws and otherparts were collected from the Pleistocene deposits of American continent.
It has been shown by many authors that the structure of the skeleton in salmonid
fishes is rather primitive in several respects of the head portion, particularly greater parts
being of cartilage nature, in comparison with that of other teleostean fishes.
author has also shown this fact by a thorough osteological study.

The present

Goodrich (19()9) also

has assumed that the cranium of salmon is primitive in character being composed of aprimordial cartilage or chondrocranium, the parietals being separated by the intervention ofa supraoccipital bone, and orbitosphenoids being each other on the median line under the
cranium.

Further be pointed out the presence of a homocercal caudal fin together withthe vestiges of the spiral valve in the intestine which is €ound in many selachian fishes.
Recently, Matsubara (1955) has called his attention to Gosline’s (1952) phylogenetic
figure which deals justly with the systematic relations of the whole fish orders. According
to this phylogenetic figure, the situation of the Salmonidae corresponds to one of theprimitive fish groups which were considered to be derived from the Clupeiform members.
It is well accepted at present that the Salmonidae in Japan is composed of four genera
which are represented by Oncorhynchus, Saltno, Salvelinus and Hucho.

Among them,Oncorhynchus is shown by eight species, containing the chum, silver, chinook, pink and
Lluelmck salmon.

These species furnishes the subjects for ecological studies, especially oflate regarding oceanic conditions, such as their migration, race, population and life history.
On the other hand, Giinther (1866) has pointed out that morphological characters which
serve to distinguish between genera or species of the Salmonidae are very scanty andindistict, so that their separation is hardly possible based merely on external characters.

Since then on, a considerable work has been published on taxonomic and morphologicalstudies of the pacific salmon, as far as we know, but there is a few or no reports dealing
with the genus Oncorhynchus based on phylogenetical stand-point.

I n view of the above

situation, further studies have been much needed to obtain any critical information on thephylogenetical relationship of the Salmonidae.

Here, the writer has undertaken someobservations on this subject with a hope to obtain any data available for understanding

the relationship between interspecies of the genus Oncorhynchus, and to contribute something47

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

to the study of phylogeny in fishes.
General speaking, the morphological characters of salmon species show a wide rangeof variation among species, and therefore it is rather difficult to readily identify the specieson the basis of merely a single diagnostic element. It is then evident that a couple of atleast two or more diagnostic characters would be needed for the determination or discrimination of the species. Here, we should call attantion to the features that the external
form of the parr-staged fingerlings and gill-rakers of adults serve among the major characters as important and valuable diagnostic features for consideration of the phyletic relationships of salmon species.

With the above points in mind, the present writer has attempted

to formulate a phylogenetic system of the Salmonidae. In Figure 9, a system is represented
in which a phylogenetic relationship of the genus Oncorhynchus is summarized in the formof a systematic tree.
Generally-, the salmonid fishes are divided into two major groups, Oncorhynchus andSalrno based on certain fundamental diagnostic characters, though there are some controversies in this respect among the authors.
First of all, it should be mentioned that the genus Oncorhynchus can apparently- begrouped into two types on the basis of differences in external form in the parr fingerling:
one is represented by an elongate or rather slender form and lower depth, while the otheris shown b y non-elongate form and deeper depth in appearance. Such two types of generalappearance are generally stable under any environment. Accordingly, these major characters are considered to be of special significance in the evolutional consideration of salmon.
As indicated in Figure 9, two branches diverged from the main stem of Oncorhynchus areformulated on the basis of the features as mentioned above.
Hence, for the convenience sake in this paper, an elongate-lower stem is called A-stem
and a stumpy-deeper one B-stem. T h e species involved in the A-stem are beta, gorbuscha,

nerka and kazoamurae, while the B-stem contains the following species, tschawytscha,kisutch, nzasou and rhodurus. Both the A and B stems can be, moreover, distinguishedclearly into several groups by the morphological feature of gill-rakers of adult salmon.
The similarlity and disimilarity in size and number of the gill-rakers together with someother characters show apparently- a certain relationship among the species here considered.
T h e first divergence form of the A-stem includes two species, nerka and gjrbuscha.
They are characterized hy having slender shape and numerous gill-rakers which are almost
similar in count in both species.

T h e number of gill-rakers on the first branchial arch issomewhat larger in nerka than in garbuscha, being 33.66 as average in former and 30.42
in the latter.

Furthermore,these species are strongly humpback in form in males atspawning seasons. Based on the above features, it is reasonable to consider that gorbuscha
is more close to nerka than to other species.

However, there are some remarkable facts

that the scale and pyloric caeca are larger in gorbuscha than in nerka, as shown in Tables
1 and 8. In kawamuras, the gill-rakers are most numerous of all Oncorhynchus species,
and the shape of the raker and general body-form of this specicies bear a resemblance tothose of the land-locked nerka, though the coloration in mature fish is considerably black,48

Ecological and Morphological Studies of the Genus Oncorhynchus

S A L M O N I D A E
Figure 9.

Showing the phylogenetic interrelationships of the species belonging
to genus Oncorhynchus.

49

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

instead of the reddish color in nerka. In addition, this species comes to lose humpback
as nerka, in breeding season.

In the light of the above findings, this species is closely

related to nerka, though no observation has been made on their fingerling.

Then, it seems

probably that kawamurae branches off from a gorbuscha-nerka group of the A-stem. The
last offshoot departed from the A-stem is represented by a single species, keta, which israther short in shape and has a smaller number of gill-rakers than the g ~ r b u s c h a - n ~ k agroup.

This species is somewhat related in the form and number of gill-raker5 to thoseof kisutch, but the number of pyloric caeca is the largest in Oncorhynchus sbecies, andtherefore partly related to gorduscha in this ,point. T h e branch of k d aseeihs to arise

from the basal part under kazuarnurae offshoot, and is situated in the interspace between
nerka-garbuscha and kisutch-tschazuylscha groups belonging to the B-stem. On the other
hand, the gill-rakers range of each species belonging to the R-stem is generally overlappingin wide range in each other.

Based on this feature, a suggestion seems to be possiblethat the relationships in these species is much more closely related than in those of the
A-stem. In the first gronp of the B-stem, kisudch and tsckazuyfscha are characterized bygill-rakers rather slender in outline, and its number that is very similar in both species,
though, in tschawytscha, the counts of lateral tine, branchiostegals and fin rays such as
pectoral and anal are generally greater than in KisuZch.

Considered from the above fact

it is apparent that these two species are closely relative to one another.

This group isalso near to heta in systematic relation at least in having a similarity in size and numberof the gill-rakers.

U S ,characterized by gill-rakers
T h e last groups, masou and Y ~ G ~ ~ T areshorter in length, its number being smaller than that of other species.
of the pyloric caeca is much less than in others.

Further the number

However, the count of ventral fin rays

in masou is almost always constant, being 10 in number, but in rhodurus it shows 11 or

12 in number. Furthermore, except a remarkable fact that rhodurus shows crimson spots
along the body-side, river residents of both species are unable to be perfectly distinguishedb37 the external body-form, parr marks or other black spots.
Summarizingly it may he stated that they are closely resemblant in their relationship with
one another than in other groups, and that the offshoot of this group seems to diverge
from the basal part of the main stem. Also, this group is related to kisulch, on the basisof the fact that they have almost equal number of the gill-raker.

In the light of the above consideration, the statements may be allowed that any
morphological character of Onccrhynchus species has not been thoroughly differentiatedas yet in every part of the body, particularly in axial elements, though partly some marginal features such as branchiostegals and gill-rakers are moderately differentiated as morphological characters sufficient for taxonomical diagnosis, as have been in higher teleostean
fishes. On account of the above aspects, therefore, the major conclusion may be drawnthat the related species of the genus Oncorhynch~sshould be classified or identified mostly
by means of the examination of some marginal characters such as branchiostegals andgill-rakers at present-day-standards of taxonomic knowledge of salmonid fishes.
General speaking, the species characters consist of a few diagnostic and many other50

Ecological and Morphological Studies of the Genus Oncorh3;nchus
characters. It should not be forgotten that two populations are by no means identicalbecause they do not differ in any obvious characters. We understand by taxonomic characters
any attribute of an organism by which it may differ from other organisms.

Such charactersare, in general, morphological ones, such as size, proportions, structure, coloration, or color
pattern.

I t has been found, however, that these superficial morphological characters are

generally correlated with a considerable number of physiological and biological features.
In modern taxonmy, attention has been directed to characters which are not purely morphological, such as ecological requirements, migratory status, pairing habits, seasonal occurrence, distribution and so on. Any system or classification is based on the proper evaluationof taxonomic characters. I t is important to base systematic classification schemes on as
many characters as possible.

T h e fewer the characters used, the greater is the danger that

mistakes in the classification will be made (Mayr 1949).

V . SUMMARY
T h e principle of taxonomy and its bearing upon phylogeny was reviewed in reference
to the related literature. Morphological characters together with ecological features available for taxonomic diagnoses were investigated in the pacific salmon (Oncorhynchus,
Salmonidae), with special reference to the phylogenetical relationship of eight species of thegenus Oncorhynchus. T h e specimens on which the present investigation was based numbered over 2,877 in total.

T h e results of studies were conveniently described separaifj.

2

into four parts. Part 1 presents the results of a detailed morphological and measuremental
study of the skeleton, especially of the skull which provides the important basic characterof the body valuable for taxonomical diagnosis the chum salmon common in Hokkaido.
T h e cranium of Oncorhynchus consists in greater part of cartilaginous elements, as havebeen known in many selachian fishes, though there are some ossified bones to more orless degree around it.

Based on this fact it is apparent that the salmonid fishes are ofprimitive nature in certain struatures of the body.

Part 2 deals with a detailed analysis of

tweleve items of morphological characters which seem to serve for the taxonomic classification of the pacific salmon. T h e proper evaluation of these characters for the identificationof salmonid species was discussed on their diagnostic bases.

It was then concluded thatthe characters valuable for taxonomic diagnosis were very scarce in occurrence.

So far as

the present observations have gone, the following elements ; the gill-raker, the lateral line,
the branchiostegals and sometimes markings on the body surface, are to he useful for
diagnostic characters which serve to distinguish one species from others in the pacificsalmon. Probably the characters as mentioned above seem to be ones which are moderately
differentiated in each species here concerned.

In part 3. the meristic measurements of the

body parts, and discriptions concerning several morphological and ecological features arereviewed on each species of the pacific salmon, including the range on its geographicaldistribution, the distinguishable criterion from others, and the common names which are
generally used to many localities in Japan and foreign countries. Part 4 detailed morphological and measuremental observations were carried out on the general body form in the51

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

fingerling stage and on the gill-rakers in the abult stage in particular regard to their
phylogenetical significance, since they are shown to be valuable characters for the examination of phylogenetical relationship of the species. Based on the differences of those characters of fingerlings, the geuns Oncorhynchus is to be divided into two main stems, A
and B : they are represented by the species characterized by an elongate-lower form andIn the A-stem to be included the following species: keta,
gorbuscha, nerka, and kawamurae, while the B stem seems to cover the following species:
kisutch, tschawytscha, rhodurus and masou. T h e species in groups can be classified again

by a stumpy-higher form.

on the basis of the shape and number or gill-rakers into several groups.

In the A-stem,

kawanzurm is characterized by the highest number of gill-rakers, being 36.5 on an average,
T h e species, gorbuscha
and nerka are considered to be closely related in phylogenetical relation in having a similar

while keta shows the lowest number being 22.9 on an average.

form and number of gill-rakers, as well as in showing a similar feature in developmentof the humpback.

On the other hand, the species included into the B-stem show a cons-

iderable overlapping in gill-raker counts from each other within a certain range.

On accountof the above fact, it seem probable the these B-stem species are closely related with eachother in their taxonomic relation. It is apparent that kisutch and tschawytscha stand in acloser relationship on account of their having the same number and length of gill-rakers
as rhodurus and masou.

It is remarkable that the phylogenetic relationship of the genus Oncorhynchus is shownon the basis of the body-form in early parr-fingerling and the number and shape of gillrakers in adults.

\I.
REFERENCES
Abe, T. 1952 Taxonomic studies on the puffers (Tetraodontidae, Teleostei) from Japan and adjacentregion VIII. Concluding remarks, with the introduction of two new genera, Fugu and Boesmanichthys. Jap. Jour. Ichthy. 2 : 35-44
1958 Encyclopedia zoologica illustrated in colours 11. Hokuryu-kan Pub. Co. Ltd. Tokyo
1-392 (in Japanese)
Abe, T. and Y. Takashima 1958 Differences in the number and position of two kinds of fin-supportsof the spinous dorsal in the Japanese mackerels of the genus Pneumatophorus. Jap. Jour. Ichthy.
7 : 1-11
Andreashev, A. P. 1955 A contribution to the knowledge of the fishes from the Bering and Ghuktchi
Seas. Sp. Sci. Rep. Fish. 145 : 1-81
Barlow, G. W. 1961 Causes and significance of morphological varliation in fishes. Sys. Zool. 10:
105-117
Barsikov, V. V. 1959 Fauna of USSR-Fishes Family Acarichadidae. Jour. Zool. Inst. 5 : 1-171 (in Russian)Benke, R. J. 1959 A note on Oncorhynchus formsunurn and Oncorhynchus masou. Jap. Jour. Ichthy. 7 :151-1 52
, T. P. Koh and P. R. Needham 1962 : Status of the landlocked salmonoid fishes of Formosawith a review of Oncorhynchus m o u (Brevoort). Copeia. 2 : 400-407
Berg, L. S. 1955 Classification of fishes both recent and fossil. Jour. 2001. Inst. Moscow 20 : 1-286(in Russian)1959 Vernal and hiemal races among anadromous fishes. (Translated from Russian by52

Ecological and Morphological Studies of the Genus Oncorhynchus
Ricker). Jour. Fish. Res. Bd. Canada 16: 515-537
1961 Ichthyology. VI. Akad. Sci. Print. Moscow & Leningrad 1-746 (in Russian)Boulenger, G. A. 1904 Fishes, Ascidian etc. V11. Macmillan and Co. Ltd. New York 1-727
Buen, Fernando de 1959 LOS peces exoticos en las Aguas Dulces de Chile. Inv. Zool. Chilenas 5 :103-137
Buchus, R. H. 1957 The fishes of Labrador. Bull. Amer. Pvzus. Nat. Hist. Art IV, 113 : 277-377
Biitchli 0. 1924 Vorlesungen uber vergleichende Anatomie. Julius Springer. Berlin 1-380
Calman. W. T. 1949 The classification of animal - Introduction to zoological taxonomy. Mathen and
Co. London 1-54
Chu, Y. T. 1935 Comparative studies on the scales and on the pharyngeals and their teeth in Chinese
Cyprinidae, with particular reference to taxonomy and evolution. Biol. Bull. St. John’s Univ.
2: 1-225
Clark, F. N. 1947 Analysis of populations of the Pacific sardine on the basis on vertebral counts.
Fish. Bull. 68: 1-36
Clemens, W. C. and G. V. Wilby 1949 Fishes on the Pacific coast of Canada. Bull. 68 : 1-368
Clothier, C. R. 1950 A key to some southern California fishes based on vertebral characters. Fish.
Bull. 79: 1-83
Cole, F. J. and J. Johnstone 1901 VIII. Pleuronectes. L.M.B. Mem. London 1-252
Desler, N. N. 1957 Embryoloigcal study of Oncorhynchus keta (Wal.) from Amur river. Inst. Morph.
Jour. 20: 3-70 (in Russian)Evermann, B. W. and E. L. Goldsborough 1907 The fishes of Alaska. Gov. Print. Offic. Washington
221-360
Gehringer, J. W. 1959 Egg development and metamorp 1s of the tenpounder Elofis saurus Linnaeus.
fish. Bull. 155 : 619-674
Goldschmidt, R. 1907 Zoologisches Taschenbuch fur studierende zum Gebrauch bei V o r l e a g e n und
9praktischen Uebungen. Wirbeltiqe. Georg. Thieme 2 : Berlin 1-147
Goodrich, E. S. 1909 A treatise on zoology. M Vertebrata Craniata (First Fascicle : Cyclostomes andfishes). Adam and Charles Black Co. London 1-518
Gosline, W. A. 1959 Mode of life, functional morphlogy, and the classification of modern teleostean
fishes. Sys. ZOO]. 8 : 160-164
Gregg, J. R. 1954 The language of taxonomy-An application of symbolic logic to the study of classificatory system. Columbia Univ. Press. New York 1-70
Gunther, A. 1866 Catalogue of fishes VI. London 1-171
1880 An introduction to the study of fishes. Adam and Charles Black Co. London 1-706
0Gutberlet, J. E. 1915 On thgosteology of some of the Loricati. Illinois Biol. Monqg. 2: 1-29
Hagerman, F. H. 1951 An easy method of separating king and silver salmon. Calif. Fish and Game
37: 53-56
Hertwig, 0. 1906 Handbuch der vergleichenden und experimental Entwicklungslehre der Wirbeltiere.
B. 2 : Gustan Fischer. Jena 1-890
Hikita, T. 1930 Flatfishes found in northern Japan. Bull. School Fish. Hokkaido Univ. 4 : 178-295(in Japanese)
1956 On the anatomy and develoment of carp in Hokkaido. Sci. Rep. Hokkaido Fish Hatch.
11 : 65-96 (in Japanese)
Hikita, T. Jr. 1951 Fishes of Volcano Bay in Hokkaido. Jap. Jour. Ichthy. 1 : 306-313~1953 A note on the fry of the fry of salmonid fishes rearing in the artificial hatchery in
Hokkaido, with special reference to the discrimination of these salmon fry. Sci, Rep. Hokkaido Fish Hatch. 8: 11-20 (in Japanese)
1954 On the common names of the salmonoid fishes and their related forms found in northern
Japan and its adjacent waters. Sci. Rep. Hokkaido Fish Hatch. 9 : 137-145 (in Japanese)
1955 An aberrant form of the dog salmon with abnormal scales. Jap. Jour. Ichthy. 4 : 133-135
1955 On the aberrant form of the chum salmon taken from the northern Pacific Oceanand some examples of salmonoid fishes in Hokkaido. Sci. Rep. Hokkaido Fish Hatch. 10: 63-71(in Japanese)____
1956 Pacific salmon (Genus: Oncorhynchus) kqown to occur in coasts and rivers within
Hokkaido. Sci. Rep. Hokkaido Fish Hatch 11 : 25-44 (in Japanese)%53

Scientific Reports of the Hokkaido Salmon Hatchery No. 17
1957 A preliminary list of fishes from the northern Pacific Ocean. Jour. Fac. Sci. Hokkaido
Univ. Ser. VI, Zool. 4: 162-164
katas (Walbaum). Sci. Rep. Hokk1958 Occurrence of the mottled dog-salmon, O n c o ~ h ~ u c h u
aid0 Salmon Hatch. 12: 45-49 (in Japanese)
Hoar, W. S. 1958 The evolution of migratory behaviour among juvenile salmon of the genus OncoYhynchus. Jour. Fish. Res. Bd. Canada 15: 391-428
Horie, S. 1961 Pleistocene stratigrap hy in Japan, North America and Furope (1). Quat. Res, 2 : 15-22(in Japanes)
1961 Paleolimnological problems of Lake Biwa-ko. Mem. Coll. Sci. Kyoto Ser. B. 28: 53-71
Hotta, H. 1955 On the mugilid fish from Kobashima, Nagasaki, Japan, with additional notes on theintestinal concolution of Mugilidae. Jap. Jour. Ichthy. 4 : 162-169 (in Japanese)
1958 Abnormal development of the cranial bones of ‘‘Jack mackerel” Trachzl~usjaponicus
Temminck and Schlegel with the growth. Jap. Jour. Ichthy. 7 : 115-117 (in Japanese)
Hotta, H. 1961 Comparative study of the axial skeleton of Japanese teleostei. Fish. Rep. 5 : 1-155(in Japanese)
Hubbs, C. L. 1922 Variations in the munbers of vertebrae and other meristic charactars of fishes
correlated with the temperature of water during development. Amer. Nat. 61 : 360-372____ 1945 Phylogenetlc postion of the Citharidae, a fmily of flatfishes. M i x . Pub. Mus. Zool.
Univ. Michigan. 63 : 1-38
Ishiyama, R. 1951 Revision on the Japanese mugilid fishes, especially based upon the osteologicalcharacters of the cranium. Jap. Jour. Ichthy. 1 : 238-248 (in Japanese)Iwai, T. 1955 Osteological annotations on the skull of the land-locked ‘‘Ayu’’, filecoglossus altivelis
Temminck and schlegel. Bull. Jap. SOC.Sci. Fish. 21 : 311-313
1958 Development of the com-like teeth in a salmonoid fish, Olecoglossus altivelis Temminck
and Schlegel. Bull. Jap. SOC.Sci. Fish. 22 : 12-16
Jordan, D. S. and B. W. Evermann 1896 T h e fishes of north and middle America: A descriptive
catalogue of the species of fish-like vertebrate found in the waters of North America, Northof isthmus of Panama (Part 1). Gov. Print. Offic. Washington 1-1240__- and J. 0. Snyder 1902 A review of the salmonoid fishes of Japan. Proc. 1J.S Nat. Mus. 24 :365-366
Jordan, D. S. and M. Oshima 1919 : Salmo Jormosanus, a new trout from the mountain streams o f
Formosa. Proc. Acad. Nat. Sci. Phil. 71 : 122
1925 Fishes. Appleton and Co. New York 1-773- ___ and C. L. Hubbs 1925 Record of fishes obtained by Devid Starr Jordan in Japan. 1922.
Mem. Carnegie Mus. 10 : 93-346
Kafuku, T. 1958 Specification in Cyprinid fishes on the basis of intestinal differentiation, with somerefer-ences to that among Catostomids. Bull. Freshwater Fish. Lab. 8 : 45-75
Katayama, M. 1959 Studies on the serranid fishes of Japan (1). Bull. Fac. Educ. Yarnaguchi Univ. 103180
Kishinouye, K. 1923 Contribution to the comparative study- of the so-called scombrid fishes. Jour.
Coll. Agr. Tokyo Imp. Univ. 8 : 293-275
Kitahara, T. 1904 Preliminary note on the salmon and trout of Japan. Ann. 2001. Jap. 5 : 117-120
Kohn, A. J. and G. A. Orians 1962 Ecological data in the classification of closely related species.
Sys. 2001. 11 : 119-127
Kubo, T. 1950 A Preliminary report on the study on the groups of Oncorhjnchus beta (Walbaum)(dog salmon) and the numbers of their segments. Bull. Fac. Fish. Hokkaido Univ. 1 : 1-11 (inJapanese)____ and T. Kobayashi 1953 Some populations of dog-salmon (Oncor nchus ketn (Walbaum) (inIshikari river system, Hekkaido, and the numbers of their vertebrae and lateral line scales.
Bull. Jap. Suc. Sci. Fish. 19; 297-302 (in Japanese)
1956 Peculiarity of Population of chum salmon in the Shiriuchi river in respect to thevertebral count. Bull. Fac. Fish. Hokkaido Univ. 6 : 266-270 (in Japanese)~ _ _ _1958 A note on the age and race of the red salmon in the North Pacific Ocean. Bull. Fac.
Fish. Hokkaido Univ. 8 : 304-309 (in Japanese)
Kuronuma, K. 1943 Osteological study on Japanese fish (1). Comparative osteology, especially of254Ecological and Morphological Studies of the Genus Oncorhynchus
cranial characteristics in Tetraodonid genera Lagocephulus and Spheroides. Bull. Res. Inst.
Resor. 1 : 119-130
Lang, A. 1891 Text-book of comparative anatomy (Part 1). Macmillan Co. New York 1-562
Lindkrg, G. U 1959 A list of the fauna of the sea waters of the South Sakhalin and South Kuril
Islands. Jour. 2001. Soviet Acad. Sci. 6 : 173-245 (in Russian)
Lindsey, C. C. 1955 Evolution of meristic relations in the dorsal and anal fins of teleosts. Trans.
Roy Soc. Canada. Ser. 111. 40 : 25-49
Macfarlane, J. M. 1923 The evolution and distribution of fishes. Macmillan Co. New York 1-564
Makino, S. 1950 A review of the chromosome numbers in animals. Hokurykan Co. Tokyo 1-213 (inJapanese)
Malloch, P. D. 1910 Life history and habits of the salmon, sea trout and other freshwater fish. Adamand Charles Black, London 1-264
Marr, J. C. 1957 The Problem of definding and recognising subpopulations of fishes. Sp. Sci. Rep.
Fish. 208: 1-6
Marshall, A. M. 1899 Practical zoology. Spottiswoods and Co. London 1-486
Marshall, W. 1924 Bilderatlas zur Tierkunde mit beschreibendem Text (Zweit TeiI). Bib. Inst. Leipzig
1-48
Matsubara, K. 1943 Studies on the scorpaenid fishes of Japan, anatomy and taxonomy (1-11). Cont. Res.
Inst. Nat. Resor. 20: 1-486
1955 Fish morphology and hierarchy. Part 1. Ishizaki Pub. Co. Tokyo 1-789 (in Japanese)and A. Ochiai 1955 A revision of the Japanese fishes of the Family Platycephalidae (theflathead). Metn. Coll. Agr. Kyoto Univ. Fish. Ser. IV 68 : 1-109
Mayr, E. 1949 Systematics and the origin of species. Columbia Univ. Press. New York
Mond, T. 1960 A Propos du Pseudobranchium des Anternnarius (Pisces, Lophiformes). Bell. Ser. A
22 : 620-698
Mori, 0.1927 Notes on the development of the skull of Lepidosteus osseus Zool. Mag. 39 : 282-297 (inJapanese)
Neave, F. 1958 The origin and speciation of Oncorhynchus. Trans. Roy. SOC. Canada Ser. 111 Sec. V
52 : 25-39
Ncedham, P.R. and R. Gard 1959 Rainbow trout in Mexico and California with notes on the cutthroat
series. Univ. Calif. Pub. Zool. 67: 1-124
Nikolsky, T. V. 1954 General ichthyology. Soviet Sci. Moscow 1-458 (in Russian)Nogusa, S. 1960 A comparative study of the chromosomes in fishes with particular considerations ontaxonomy and evolution. Mem. Hyogo Univ. Ser. 111. 3 : 1-62
Nomura, M. 1953 On the taxonomic characters in the mouth cavity of salmonoid fishes. Jap. Jour.
Ichthy. 2 : 261-271 (in Japanese)
1954 On the taxonomic characters in the mouth cavity of salmonoid fishes. 11. Pacific salmon. Jap. Jour. Ichthy. 4 : 162-169 (in Japanese)
Norden, C. R. 1961 Comparative osteology of representative salmonid fishes with particular reference
to the grayling (Thj.maZlus arcticus) and its phylogeny. Fish. Res. Bd. Canada 18 : 679-791
Ochiai, A. 1953 Comparative studies of branquillos of the genus Branchiosteus found in the waters ofJapan and China. Zool. Mag. 62 : 306-313 (in 'Japanesej
Okada, S. 1939 The silver salmon taken from Hokkaido. Bot. Zool. 7 : 113-ll&(in Japanese)
Okada, Y. and K. Suzuki 1956 On the similarity of the osteological characters found between Owstonidae and Cepolidae. Rep. Fac. Fish. Pref. Mie Univ. 2 : 185-194
1959-1960 Studies on the freshwater fishes of Japan. Pref. Univ. Mie 1-860
Ohta, Y. 1918 On the gill-rakers of Salmonidae. Sui-san Kaiho 2 : 261-266 (in Japanese)
Oshima, M. 1957 Studies o n the dimorphic salmon, Oncorhynchzis masou (Brevoort) and Oncorhpzchus
rhodurz4s Jordan and McGregor, found in Japan and adjacent territories. Nire Pub. Co. Sapporo 1-79 (in Japanese)
Parker, T , 1884 Zootomy. Clay Sons, and Tayler Print. London 1-397
Pimental, K. A. 1958 Taxonomic methods, their bearing on subpopulation. Sys. Zool. 7 : 139-156
Pomini. F. P. 1939 Studi sullo svillupo della trote Italiano. 4 : Studi larvali e primi stadi postlarvalidella trote del piave (Sulmo marmoratus Cuv.). Arch. Zool. 27 : 407-428____
1940 Rickrches sur Sulmo macrostigma Dum. Biol. Fasco. 3 : 13-63~~

55

Scientific Reports of the Hokkaido Salmon Hatchery No. 17
Ridgeway, G. J. 1957 The use of immnological techniques in racial studies. Sp. Sci. Rep. Fish. 208 :39-43
Rounsfell, G. A. and W. H. Everhart 1953 Fisheries science: Its methods and applications. John
Wilbey and Son Inc. New York 1-444-~
1957 Fecundity of North American salmonidae. Fish. Bull. 57: 451-468
1958 Anadromy in North American salmonidae. Fish. Bull. 58: 171-185
Saito, S. 1950 The embryological study of fishes. 1. General observation on the early development of
dog salmon, Oncorhqnchus keta Walbaum. Jour. Fac. Agr. Hokkaido Univ. 48 : 267-289
Sakamoto, K. 1935 On the so-called “Hanamagari”, curved snout of chum salmon. Yoshoku Kaishi, 5 :137-138 (in Japanese)
Sano, S. 1959 The ecology and paopagation of genus Oncorhynchus found in northern Japan. Sci. Rep.
Hokkaido Salmon Hatch. 14: 21-90 (in Japanese)
Sato, R. 1954 Fisheries biology of pond smelt HypOmesus olidus (Pallas). Aquiculture Sci. 5 : 1-99 (inJapanese)
Sato, Sh. 1935 The fauna of Akkeshi Bay VI. Pisces. Jour. Fac. Sci. Hokkaido Univ. Ser. VI 2001.
6 : 13-34
Shapovalov, L. 1941 The freshwater fish from California. Pacif. Sci. 3 : 441-446
and A. C . T a f t 1954 The life histories of the steelhead rainbow trout ( S a l m gairdnere‘
gairdnerz) and silver salmon (Oncorhynchus kisutch). Fish Bull. 98 : 1-375
Schmidt, P. F. 1950 Fishes of Okhotsk Sea. Sov. Acad. Sci. Moscow 1-370 (in Russian)S-chultz, L. P. and H. A. Hanson 1935 Salmonid game fishes in the National Forests of .northeastern
United States. U. S. Dep. Agr. For. Serv. Seattle 1-26
Seymour, A. 1959 Effects of temperature upon the formation of vertebrae and fin rays in young chinook salmon. Trans. Amer. Fish. SOC.88: 58-69
Simpsun, G. G. 1945 The principles of classification and a classification of mammals. Bull. Amer.
Mus. Nat. Hist. 85: 1-350
Slastenenko, E, 1958 The freshwater fishes of Canada. Kief printer. Tronto 1-385
Sneath, P. H. A. 1961 Recent developments in theoretical and quantitative taxonomy. Sys. Zool. 10:
118-139
Smith, H. M. 1958 The synthetic natural populational species i n biology. Sys. 2001. 4 : 116-119
Soldatov, V. K. and G. U. Lindberg 1930 A review of the fishes of the seas of the Far East. Bull.
Pacif Sci. Fish. Inst. 5 : 1-407 (in Russian)
Suehkro, Y. 1942 A study on the digestive system and feeding habits of fishes. Jap. Jour. Zool. 10:
1-303
Takagi, K. 1950 On the glossohyal bone of the gobioid fishes of Japan, with some phylogenic considerations. Jap. Jour. Ichthy. 1 : 37-62 (in Japanese)and Y. Kobayashi 1958 Vertebral characters of a congrid fish, Asteroconger myrimter, takenfrom the Tokyo Bay. Jour. Tokyo Univ. Fish. 44: 51-55
Takahashi, N. 1952 Revision of the names of head bones of Cyprinus carpio and Carussius aurutus.
Jap. Jour. Ichthy. 2 : 196-205 (in Japanese)
Taranetz, A. L. 1937 Handbook on i d e n t i f i k a t i o n of fishes of Soviet Far East and adjacent waters. Bull. Pacific. Sci. Inst. Fish. Ocean. 11 : 1-274 (in Russian)Tchernavin, V. 1923 Skulls of salmon and trout-A brief study of their differences and breedingchanges. Sal. Trou. Mag. 31 : 235-242
1932 The mystery of a salmon’s kype-Does it serve any purpose? Sal. Trou. Mag. 90: 37-44
Teng, H. T. 1959 The morphology and ecology of the land-locked salmonids in Formosan mountains.
Taiwan Fish. Res. Inst. 5 : 77-82 (in Chinese)
Uchihashi, K. and K. Inoue 1940 Some observations of vertebral column in Madai (Pagrostomus major
Temminck and Schlegel). Bull. F i s h Exp. St. Hyogo-ken 2 : 33 (in Japanese)and M. Nakamura 1950 The variation in the number of the vertebrae of the sandeel (Ammodqtes personatus Girard) in Japan. Bull. Fish. Exp. St. Hyogo-ken 9 : 29-34 (in Iapanese)
H. Shimomura and 0. Sano 1957 External form of the brain in Japanese salmonoid fishes
and its ecological meaning. Ann. Rep. Japn Sea Reg. F i s h Res. Lab. 3 : 97-116 (in Japanese)
1953 Ecological study of the Japanese teleosts in relation to the brain morphology. Bull.
Japan Sea Reg. Fish. Lab. 11 : 1-166 (in Japanese)56Ecological and Morphological Studies of the Genus Oncorhynchus
Valvirta, E. J. 1932 llntersuchungen iider die kleinmarane (Coregonus albula L.) das vaasa Acharenhofs im Bottnischen Meerhusen. Ann. Zool. Sci. 1 : 1-45
Vladykov, V. D. 1954 Taxonomic characters of the eastern North America chars (Salvelinus andCristiwrmer). Jour. Fish. Res. Bd. Canada 11 : 604-932
1956 Fecundity of wild speckled trout (Salvelinus fontinalis) in Quebec lakes. Jour. Fish.
Res. Bd. Canada 13 : 799-841
1962 Osteological studies on Pacific salmon of the genus Oncorhynchus. Bull. 136 : 1-172
Walters, V. 1953 The fishes collected by the Canadian Arctic Expedition, 1913-18, with additional
notes on the ichthyofauna of western Arctic Canada. Bull. 128 : 1-18
1956 Fishes of westsrn Arctic America and eastern Arctic Siberia. Bull. h e r . Mus. Nat.
Hist. Art V. 106 : 26-267
White, M. J. D. 1954 Animal cytology and evolution. Cambridge Press. London~.
1957 Some general problems of chromosomal evolution and speciation in animals. Serv.
Biol. Prog. 3 : 109-147
White, M. J. D. 1957 Cytogenetics and systematic entomology. Ann. Rev. Entomol. 2 : 71-90
Widrig, T. M. and B. A. Taft 1957 Measurement of population movement by observation of meristic
or morphometric character. Sp. Sci. Rep. Fish. 208: 29-34
Willimovsky, N. J. 1954 List of the fishes of Alaska. Stanf. Ichthy. Bull. 4 : 279-294

57

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

EXPLANATION OF PLATES
1.
Fig. 10. The general aspect of the endoskeleton showing the vertebral column and their several
bones supporting the body of the chum salmon (Oncorhynchus beta).
1. Zygapophysis : 2. Epipleural ; 3. Anterior facet of the first vertebra for the occipital condyle ;4. Neural spine ; 5. Interneural spines ; 6. Ribs ; 7. Axonosts ; 8. Interhaemal spines ; 9. Haemal
spines; 10. Urostyle; 11. Hypurals; D. Dorsal f i n ; Ad. Adipose f i n ; A. Anal f i n ;Plate

Plate 2.
Fig: 11. Laterai view of bones forming the skull and the outline of the pectoral girdle from left
side in male salmon.
1. Supraoccipital ; 2. Supraoccipital crest ; 3. Sphenotic ; 4. Epiotic. ; 5. Opisthotic ; 6. Pterotic ;7. Orbitosphenoid ; 8. Alisphenoid ; 9. Frontal ; 10. Mesethmoid ; 11. Prefrontal ; 12. Parietal ;13. Nasal ; 14. Nasal cavity ; 15. Hyomandibular ; 16. Symplectic ; 17. Quadrte : 18. Mesopterygoid ; 19. Metapterygoid ; 20. parasphenoid ; 21. Pterygoid ; 22. Palatine; 23. Articular ; 24. An,
gular ; 25. Dentary ; 26. Premaxillary ; 27. Maxillary ; 28. Jugale or supplementary ; 29. Operculum ; 30. Suboperculum ; 31. Interoperculum ; 32. Preoperculum ; 33. Glossohyal ; 34. Posttempral ; 35. Supraclavicle ; 36. Clavicle ; 37. Postclavicle ; 38. Coracoid ; 39. scapula ; 40. Radials; 41. Branchiostegal rays.
Fig. 12. Side view of the skull in female salmon showing superficial bones.
1. Mesethrnoid ; 2. Nasal ; 3. Frontal ; 4. Parietal ; 5. Supraoccipital crest ; 6. Opisthotic ; 7 Pterotic ; 8. Hyomandibular ; 9. Premaxillary ; 10. Maxillary ; 11. Supramaxillary ; 12 Dentary ;13. Articular; 14. Angular; 15. Quadrate; 16. Pterygoid; 17. Palatine; 18. Preoperculum;
19. Interoperculum ; 20. Suboperculum ; 21. Operculum ; 22. Supraorhital ; 23. Prefrontal;
24. Suborbitals ; 25. Branchiostegal rays ; 26. Musculus masseter ; 27. GLossohyal ;Prate 3.
Figs. 13-15. Lateral (1% dorsal (14) and ventral (15) aspects of the chondrocranium, including sitesof the articulated facets of the cranial bones and others.
1. Mesethmoid ; 2. Rostra1 cartilage; 3. Prefrontal ; 4. Nasal ; 5. Frontal : 6. Parietal ; 7. Supraoccipital; 8. Exoccipital : 9. Occipital cartilage; 10. Pterotic; 11. Sphenotic; 12. Alisphenoid;
13. Parasphenoid ; 14. Orbitosphenoid ; 15. Vomer ; 16. Semicircular canal ; 17. Epiotic ; 18. Palatine; 19. Knob;
Plate 4.
Figs. 16-18. Lateral (161, dorsal (17) and ventral (18) aspects of the cranium, especially showing several
bones around the chondrocraniurn.
1. Mesethmoid; 2. Nasal; 3 Frontal: 4. Prefrontal; 5. Sphenotic; 6. Parietal; 7. Epiotic;
8. Supraoccipital crest; 9. Pterotic; 10. Exoccipital ; 11. Basioccipital ; 12. Opisth-otic ; 13.
Prootic ; 14. parasphenoid : 15. Alisphenoid ; 16. Orhitosphenoid ; 17. Vomer ; 18. Vo-merian
teeth; 19. Orbit; 20. Foramen of trigemino-facial nerve, 21. Exit of eye muscle; 23. Ar;
ticular facet for hyomandibular ; 24. Nasal cavity:
Plate 5.
Fig. 19. Hind view of the cranium. 1. Pterotic; 2. Exoccipital; 3. Occipital condyle; 4. Parasphenoid ; 5. Epiotic ; 6. Supraoccipital crest ; 7. Opisthotic ; 8. Foramen magnum ; 9. Paraoccipital
condyle ;Fig 20. Parietal (left side). Fig. 21. Sphenotic (left side).
Fig. 22. Epiotic (left side). Fig. 23. Opisthotic (left side).
Fig. 24. Pterotic (left side) - 1. Lateral and 2. Inner views.
Fig. 25. Prootic (ventral aspect). Fig. 26. Alisphenoid (ventral aspect).
Fig. 27. Supraoccipital-UorsaI (l), ventral (2) and lateral (3J views. Ssc. Depression of semicircular
canal.
Plate 6.
Fig. 28. Lateral (1) and ventral (2) aspects of the vomer.
Fig. 29. Ventral (I), dorsal (2) and lateral (3) aspects of the parasphenoid with 4 foramens of bloodvessels.
Plate 7.
58

Ecological and Morphological Studies of the Genus Oncorhqnchus
Fig. 30. Dorsal view of the mesethmoid. Fig. 31. Lateral view of left nasal.
Fig. 32 Dorsal view of the prefrontal. Fig. 33. Dorsal (1) and ventral (2) aspect of the frontal
Plate 8.
Fig. 34. Bones surrounding the eye muscle groove (ventral view).
0.Orbitosphenoid; Of. Pores of optic nerve; A. Alisphenoid: B1. Site of brain case; P. Prootic ; Tff. Trigemino-facial foramen ; E. Exoccipital ; B. Basioccipital ; Emg. Eye muscle groove ;Fig. 35. Hind (I), front (2) and lateral (3) views of the orhitosphenoid with opening of the optic
nerve.
Fig. 36. Lateral (I), ventral (2) and hind (3) views of Basioccipital with paroccipital and occipital
condyle, and shallow depression of the eye muscle groove.
Plate 9.
Fig. 37. Relationships showing several hones of the cranium.
1. Sphenotic ; 2. Parietal ; 3. Supraoccipital ; 4. Epiotic ; 5. Prefrontal ; -Pt. Pterotic. P. Parietal. S. Supraoccipital. F. Frontal. E. Epiotic. Nc. Nasal cavity.
Fig. 38. Ventral view of bones surrounding the foramen magnum.
A. Alisphenoid ; S. Sphenotic ; Pt. Pterotic ; P. Prootic ; E. Exoccipital ; Sc. Supraoccipital
crest ; Ec. Condyle for the first vertebra ;Fig. 39. Ventral view of left and right exoccipitals. Em. Foramen n a g n u m ; Oc. Occipital condyle;
Bp. Process of the basioccipital ;Plate 10.
Figs. 40-41. Lateral views of anterior part of some vertebral column.
Z. Zygapophysis ; De. Dorsal ligament ; V. Vertebral column; E. Epipleural ; R. Ribs ; Af. Anterior facet for paroccipital condyle; Do. Dorsal aorta; S. Spinal c e r d ; N. Neural spine;
Fig. 42. Frontal view of the first vertebra.
Fig. 43. A neural spine.
Plate 11.
Fig. 44. Lateral (1) and front (2) views of the abdominal vertebrae.
Z . Zygapophysis ; De. Dorsal ligament ; V. Vertebral column ; E. Epipleural ; R. Rihs ; K. Neural spine ; S. Spinal cord ; D. Dorsal aorta ;Fig. 45. Lateral (1) and front (2) views of caudal vertebrae.
N. Neural spine; Nc. Neural canal; V. Vertebral column; H. Haemal spine; Hc. Haemal
spine ; Hc. Haemal canal ;Plate 12.
Fig. 46. Dorsal (1) and ventral (2) aspects of the branchial apparatus.
Fig. 47. Lateral view of the gill arch with gill-lamella. R. Gill-rakers; T. Tongue; S. Septum; B.
Trace removed hyoid arch ; L. Gill-lamella ;Plate 13.
Fig. 48. Dorsal view of the branchial apparatus.
I-V. First to fifth branchial a r c h ; 8,-8,. First to fourth basihranchial bone ; H. Hypobranchial ;C. Ceratobranchial ; E. Epibranchial ; P. Pharyngobranchial ; U. Upper pharyngeal teeth ; L.
Lower pharyngeal teeth ; G. G lossohyal ;Plate 14.
Fig. 49. Ventral (1) and lateral (2) aspects of the hyoid apparatus.
G. Glossohyal ; H. Hypohyal ; C. Ceratohyal ; E. Epihyal ; U. Urostyle ; I. Interhyal ; B. Branchiostegal rays ; B,-B,. Basibranchials ; Vg. Depression for blood vessel groove ;Plate 15.

Figs. 50-51. The skeleton of the dorsal (50) and anal (50) fins.
F. F i n rays consisting of unbranched and branched parts ; A. Axonosts ; B. Basinosts ; M. Musculus lavator pinnae Dorsalis ; V. b~usculuslavator pinnae analis ; E. Dorsal musculus extensor pinnae caudalis ; C. Ventral musculs extensor pinnae caudalis ;Plate 16.
Fig. 52. Lateral view of several bones constituting the caudal fin. T h e posteriormost parts of thecaudal indicating in (I), two small bones supporting a urostyle in (2) and general aspect in (3).

U. Urostyle ; Ur. Uroneurals ;S. Spinal cord ; E. Epurals ; Hy. Hypurals ; V. Vertebral column ;59

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

N. Neural spine; H. Haemel spine; Cbp. Caudal bony plate ; D. Developed rays; R.
Undeveloped 06 regeneratedrays ;Plate 17.
Fig. 53. Lateral view of the left pectoral girdle and its fin.

Pt. Posttempral ; Sc. Supraclavicle; P. Postclavicles ; CI. Clavicle ; C. Coracoid ; S. Scapula ;R. Radials ; F. Fin rays ; Sf Scapula fenestra ;Fig. 54. Ventral view of the pelvic girdle.
B. Basalia ; Pf. First ventral fin ; Cp. Cartilaginous process of the bassalia ;Plate 18-20.
Figs. 55-61 Lateral views of the gill-rakers on the first branchial arch in each species indicating
the differences of their arrangement, form and spicules.
55. gorbuscha; 56 nerka ; 57. tschawytscha f 58. kisutch ; 59 masou ; 60. rhodurus ; 61 keta ;Plate 21.
Fig. 62. Caudal outline indicating some features of Oncorhynchus species.
A. keta; B. nerka; C. kisutch; D. masou; E. rhodurus; F. gorbuscha; G. tschawqtscha;
Plete 22-25.
Figs. 63-69. Sexual dimorphism on the facial parts of Oncorhynchus species. Above ; male.
Below; female.
63. keta ; 64. nerka ; 65. kisutch ; 66. tschawytscha ; 67. rnasou ; 68.rhadurus ; 69. gorbuscha

63

Ecological and Moropholgical Studies of the Genus Oncorhgnchus

Plate 1
Fig. 1061

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

Plate 2
Fig. 112

1

Fig. 12

5
4

I

9\

\

-19

20

Ecologieal and Morphological Stndies of the Genus Oncorhynchus

Plate 3Fig. 13
5

'

IT

11

1

I

13

Fig. 15

Fig. 14

2

R

/

\

\

3

17

lb

63

n

Scientific RepoJts of the Hokkaido Salmon Hatchery No. 17

Plate 4
Fig. 16

9

12

Fig. 17

Fig. 18

4

I

8

\

7

64

Ecological and Morphological Studies of the Genus Oncorhzynchzcs

Plate-5
Fig. 195

1

4

Fig. 20

Fig. 21

Fig. 22

Fig. 25

Fig. 24

Fig. 26

Fig. 27

3

2

65

Fig. 23

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

Plate 6
Fig. 28

1

2

Fig. 29'

J

66

Ecological and Morphological Studies of the Genus Oncorhnychus

Plate 7
Fig. 30

Fig. 32

Fig. 31

Fig. 33

67

Scientific Reports of the Hokkaido Salmon Hatchery NO. 17

Plate 8Fig. 34i'HC----

I'-

Fig. 35

1

2

3

Fig. 361

3

68

Ecological and Morphological Studies of the Genus Oncwhnychus

Plate 9Fig. 37

Fig. 38

Fig. 39b-P

E-

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

Plate 10

Fig 40Fig. 412

Fig. 42

Fig. 432

70

Ecological and Morphological Studies of the Genus Oncavhynchus

Plate 11
Fig. 4.5

R

Fig. 45

Scientific Reports of the Hokkaido Salmon Hatchery NO. 17

Plate 12Fig. 46

Fig. 47i'

Ecological and Morphological Studies of the Gems Oncovhymhus

Plate 13
Fig. 4873

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

Plate 14
Fig. 49

E-

74

Ecological and Morphological Studies of the Genus Oncorhynchus

Plate 15
Fig. 50

A

Fig. 5175

Scientific Reports of the Hokkaido Salmon Hatchery NO. i7

Plate 16
Fig. 52

V

76

Ecological and Morphological Studies of the Genus Oncorhynchus

Plate 17
Fig. 53

-’

I

C

77

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

Plate 1878

Plate 19

In

.-

Q
Y

79

Ecological and Morphological Sttldiks of the G e n p Olacoshqnchus

Plate 21
Fig. 6282

Ecological and Morphological Studies of the Genus OncouhjnchustPlate 2383

Salmon Hatchery No. 17

Ecological and Morphological Studies of the Gems Olzcclrla~.nchus

Plate 25
Fig. 69

85

Scientific Reports of the Mokkaido Salmon Hatchery No. 1

Plate 26
1. Oncovhjnchus kcta (Walbaum) Above : Male, Belew : Female.
2.

Oncovhjnchus kisutch (Walbaum) Above : Male, Below : Female.

86

Ecological and Morphological Studies of the Genus Oncorhynchus

Plate 2687

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

Plate 27
1.
2.

Oncorhjnchus govbuscha (Walbaum) Above : Male, Below : Female.
Oncorhjnchus nerka (Walbaum) Above : Male, Below : Female,88

Ecological and Morphological Studies of the Genus Oncorhynchus

Plate 2789

Scientific Reports of the Hoqka!do Salmon Hatchery No. 17

Plate 28
1. Oncorhynchus tschazuytscha (Walbaum)
2.

Oncorhynchus kawamurue Jordan and McGregor Above : Male, Below : Female.

90

Ecological and Morphological Studies of the Genus Oncorhymhs

Plate 2891

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

Plate 29
1. Oncorhynchus masou (Brevoort) Ahove : Male, Below : Fernale.

2. Onco~hynchusrhodurus Jordan and McGregor

92

Ecological and Morphological Studies of the Genus Oncorhynchus

Plate 2993

Scientific Reports of the Hokkaido Salmon Hatchery No. 17

Plate 30
1.

River residents of Oncorhynchus rlzodurus Jordan and McGregor, and2.

Oncorhynchus masou (Brevoort).

94

Ecological and Morphological Studies of the Genus Oncorhynchus

Plate 30

95

Scientific

Reports uf the HOkkaido

Salmon

サケ 屈，魚類の生態学 ・形態学的研究

Hatchery N0.

t7

特に系統との 関係

ヱの 研究は太平洋
産サケ属8 種の分類，形態および十態特徴を検討し，それらの系統的類縁関係を明らかにする。 これらの結果を便宜上 4 部に分け次の如 く記述することができる。
即ち出サるためにおこなわれたものであケ属の内 北海道で最も多く漁畦されるサケ (O%nc 。 杣川。 伽5 &gfa)

を代表魚種として，詳細な骨格学的研究を行なった。その結果，サケの竹格は他の硬骨魚類より軟骨が多く，各 円 ・の癒合は完全でない。
骨格の中で最も顕著
・な形態的特徴のみられるのは頭蓋骨である，これは脳を収容する軟竹部分と，その周囲に軟甘および膜甘超原の多くの化骨分化した頭蓋付からなっている。
前者を原頭蓋(Chondrocranium)といって，終生この軟骨構造を， ―部は骨化されもつ鮫類をふくむ軟骨魚類の如き頭蓋骨を残存している。
後者は末だ軟竹部分をもつけれども
原始的な要素と，分化した要素とを兼備してた分化した諸甘からなる。要するに，この 類は骨格の構成においている魚頑といらことができる。
即ち系統的にも円惜の構造上から，軟骨魚類と他の硬骨魚類の中間的存在をなすとともf イワシ型魚類(Clupeiformes) のうちでも，より原始型を保っている―群であるとい5 ことができる。

(2)サケ属各種の形態学的および分類学的研究に採用されている
諸形質の再考察: サケ属の各種は非常に相似かよっている特徴が多いために，各種類を形態学的に類別することが極めて困難とされている。
それ故現在
迄 多くの
研究者によづて種々の形質が種の特徴として
指適され，その分類に採用されてきた。
それらの形質のうちで主なもの l2 項口を選定 (l 部新しいものを包む) し ，それら各項日の再考察をおこない， どの程痩それらの形質が種の同走，識別に役立っか調べた。
各項日の測定値を検討すると，かなり山の広い分布がみられる。
また各種問でもこれらの範明が互いに屯複している。このことはサケ属 各種が―つの形質だけでは完全に類別することが困難なもので，その分類には少なくとも
2 つ以上の形質によづて綜合的におこなわなげればならぬことを暗示している。 即ちサケ類は未だ充分に形質分化がなされていない魚類ということができる。
これは他の分化した
硬骨魚類

より分頼が至難とされている
形態的根拠であろう。l2唄口中比較的類別
E 役立つものとしては側線鱗， 鰍紹， 鯛。
条骨および斑紋などをあげることができる。
(3)サケ類の稚魚と成魚の外部形態の
相逆性および類似性の検討なら成魚の比絞形態学的研究をおこなった
結果，香びに各種成魚の形態計測と生態の記載 : サケ属 各種の稚魚および相異なっていることが分る，即ちサケ憾 稚魚には，この 科持有な Pa ， r
種の形質，団 紋が碓魚と成魚とで大いに

柵 rk (カラフトマスを除く ) が体側に沿ってならんでいるが，生長するに従って消失する。反対に各種に独特な成魚の斑点，斑紋は生長するに従って順次発現して来る。 そ九故に稚魚
允育段階中の P ， 。

「

maI 。k ， tageの稚魚は，外形および諸斑紋によって明らかに類gl することがでぎる。
更にこの stage の各種を体長，体高の関係
より 2 大別することが可能で，この関係はまた‑力でサケ属魚類の系統を諭づる上にも重要な恵義を有するものである。 各種の成魚の相違並びに煩似性は先述したごとく
稚魚とは全く別の様相を呈するので，各種の形態，生・科 魚，
態および分布について
概略検討を試みた。
川サケ屈各種相互間の系統的類縁関係: 前にも述べたごとくサケ類の系統的位置は，魚類としては下等なものに属し，比較的新しい
地質時代に進忙したものと尼、われる。したがって魚体各部の形質分化が充分でないままに残っているわげである，著者は主に形態学的特徴をもとに
老察を進
めて，サケ
属各種 (0%C0 グゆ wC 伽 s 坤gcfgs) の 頽緑を系統樹に作成し，その関係にっいて述べるとつぎの
如 くで

W ぬM5 ノは二ジマス属 (SMP叩 J から分化しているものと考えられる L属間の傾縁はある。 先づサケ属 (0%co 妨

ここでわふれないことにする) 次にサケ属は稚魚の体形から A‑ Stem
StemとB‑ ， temに分けることがでぎる。
A‑に属する魚種は，体形が細長く，体高は低く，サケ，カラフトマス， べ二マスおよびク二 マスが入る。 他

力 R‑st 。 m の体形は比較的づんぐりしており， 体局は比較的に高く，

この中にはっスノスケ， ギンマス，サク

艦sに依って若T のグルーブに分化した足跡がうか

両刀のグループは史に
ラマス，ビ ? マスが包含されている。
がえる。川ち A‑ stemの ク二 マスの鯉紺数はサケ屈 中で最も多く，平均36 ． 5 であるが，サケはA‑ stem 中で最小で平均272． 9 である。 またこの両棟は庄卵期にセコンボにならない。
カラフトマスとべ
二マスは
鯉拙の形と

数が最も近似であると共にこの2 種の雄庄卵魚では，顕著なセ コソボを呈することにより，同じ系統から分化したものであろう。他方 R‑steem に属する数種は，
ら R‑ ．steinの 各魚種間の類縁関係はA‑stem

或範囲内に於いて鰍拙数が重複している。このような市夫かの各種間の類縁関係よりも系統的に互いに極く近縁であることを物語っている。しかしながらなお
詳細に比佼してみるならばB‑ stem の マスノスケとギ
ンマスの鰍抑数は殆ん
ど似ているが，前老の方が僅かに多く，むしろサケに近い。 史にこの2 種の鯛把の 形は細長形であることが同じ

96

Ecological andMOrphologicalStudies 0f the Genus

OncorhyHchus

系統から分化したものと老えられる。残りのサクラマスとビヮマスはサケ属中で最も鯉杷数が少なく，その形も短小であるから同―系統に属するものといえる。
この2 種の最も相連する形質は，ビワマスの
体側には朱色斑点が散在するが，サクラマスにはこれがない。
また前者の
腹鰭条数は通ffilo 本であるのに対し後者では 9 本であ・る，それ故この2 種は同―祖先から分化したものと考える。
要するに現段階においては．
各魚種の稚魚期の外部形態並びに成魚期の卿榔がサケ属の系統的類縁関係を諭づる形態的特徴となり得ることが明らかになった。

97