NOAA Professional Paper NMFS 4

U.S. Department 

of Commerce

June 2006 July 2012

NOAA Professional Paper NMFS 14

An atlas of reproductive 

development in rockfishes, 

genus Sebastes

Franklin R. Shaw

J. Frank Morado

Vanessa C. Lowe

Susanne F. McDermott
NOAA Professional 

Papers NMFS

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Bruce C. Mundy

Associate Editor

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National Marine Fisheries Service 

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Ann C. Matarese National Marine Fisheries Service

James W. Orr National Marine Fisheries Service

Bruce L. Wing National Marine Fisheries Service

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NOAA Professional Paper NMFS 14

An atlas of reproductive development 

in rockfishes, genus Sebastes

Franklin R. Shaw

J. Frank Morado

Vanessa C. Lowe

Susanne F. McDermott

July 2012

U.S. Department of Commerce

Seattle, Washington
Suggested reference

Shaw, Franklin R., J. Frank Morado, Vanessa C. Lowe, and Susanne F. McDermott. 

2012. An atlas of reproductive development in rockfishes, genus Sebastes. NOAA 

Professional Paper NMFS 14, 77 p.

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iii

CONTENTS

Abbreviations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Materials and methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Morphological observations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Testis development. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

 Spermatogonia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

 Spermatocytes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

 Spermatids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

 Spermatozoa. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

 Atresia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Testis phases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Gross morphological phases of the testes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Ovary development. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

 Oogonia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

 First growth interval. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

 Second growth interval. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

 Oocyte maturation interval. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Ovary phases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Gross morphological phases of the ovary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Embryonic development. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Follicular atresia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Literature cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Professional Paper NMFS 14

iv

Abbreviations

Abbreviations associated with spermatogenesis (Figs. 1–11):

ESd early spermatid Ld Leidig cell

ESz early spermatozoa LL lobule lumen

Flag flagella LSd late spermatid

Ga primary (1°) spermatogonia LSz late spermatozoa

Gb secondary (2°) spermatogonia PSc primary (1°) spermatocyte

Gc tertiary (3°) spermatogonia RSz residual spermatozoa

Gd quaternary (4°) spermatogonia Sr Sertoli cell

IT interstitial tissue SSc secondary (2°) spermatocyte

Abbreviations associated with ovarian development (Figs. 12–24):

CN chromatin nucleolus Og oogonium

EF empty follicle=post-ovulatory follicle ON oogonial nest

EL eyed larvae OV oil vacuole

Em embryo PM prematuration oocyte

EPN early perinucleus PY primary (1°) yolk

FC follicle cell REm residual embryo

GR granulosa So somite

IT interstitial tissue SY secondary (2°) yolk

LC lampbrush chromosome Sz stored spermatozoa

LPN late perinucleus TY tertiary (3°) yolk

MN migratory nucleus Y yolk

MO mature oocyte YD yolk droplets

N nucleus ZR zona radiata

No nucleolus

Abbreviations associated with embryogenesis (Figs. 25–59):

AP auditory placode M mouth opening

Bd blastodisc NC nerve chord

Bm blastomere Noto notochord

Br brain OV oil vacuole

CM chorion membrane Ot otolith

DT digestive tract OlfV olfactory vesicle

ES embryonic shield OpC optic cup

EVL outer enveloping layer OpV optic vesicle

Ey eye PA pharyngeal arches

FF fin fold PF pectoral fin

GR granulosa PG pigment granules

He heart PL pigment layer

HF head fold So somite

L lens Y yolk

Mec Meckel’s cartilages YSL yolk syncytial layer

MF mitotic figures
1

An atlas of reproductive development in rockfishes, 

genus Sebastes

Franklin R. Shaw*

J. Frank Morado (contact author)

Vanessa C. Lowe

Susanne F. McDermott

Alaska Fisheries Science Center

National Marine Fisheries Service

National Oceanic and Atmospheric Administration

7600 Sand Point Way NE

Seattle, Washington 98115-0070

*retired

Email address for contact author: Frank.Morado@noaa.gov

Abstract—The genus Sebastes consists 

of over 100 fish species, all of which are 

viviparous and long-lived. Previous studies 

have presented schemes on the reproductive biology of a single targeted species 

of the genus Sebastes, but all appear to 

possess a similar reproductive biology as 

evidenced by this and other studies. This 

atlas stages major events during spermatogenesis, oogenesis, and embryogenesis, 

including atresia, in six species of Sebastes

(S. alutus, S. elongatus, S. helvomaculatus, S. 

polyspinis, S. proriger, and S. zacentrus). Our 

study suggests that the male reproductive 

cycle of Sebastes is characterized by 11 

phases of testicular development, with 10 

stages of sperm development and 1 stage 

of spermatozoa atresia. Ovarian development was divided into 12 phases, with 10 

stages of oocyte development, 1 stage of 

embryonic development, and 1 stage of 

oocyte atresia. Embryonic development 

up to parturition was divided into 33 

stages following the research of Yamada 

and Kusakari (1991). Reproductive development of all six species examined 

followed the developmental classifications listed above which may apply to 

all species of Sebastes regardless of the 

number of broods produced annually. 

Multiple brooders vary in that not all ova 

are fertilized and progress to embryos; 

a proportion of ova are arrested at the 

pre-vitellogenic stage. Reproductive stage 

examples shown in this atlas use S. elongatus for spermatic development, S. proriger

for oocyte development, and S. alutus for 

embryological development, because 

opportunistic sampling only permitted 

complete analysis of each respective 

developmental phase for those species. 

The results of this study and the proposed 

reproductive phases complement the 

recommended scheme submitted by 

Brown-Peterson et al. (2011), who call 

for a standardization of terminology for 

describing reproductive development of 

fishes.

Introduction

The genus Sebastes is a prolific, species-rich, and important commercial 

fish taxon in the Northeast Pacific 

Ocean. Over 100 species of the genus 

Sebastes exist worldwide, occupying a 

wide range of habitats from intertidal 

to depths >1000 m (Haldorson and 

Love, 1991; Kendall, 1991). Seventytwo species occur in the Northeast 

Pacific; however, only a few Pacific 

species of the genus Sebastes (e.g., S. 

alutus, S. caurinus, S. flavidus, and 

S. schlegeli) have been well studied. 

There is limited information on S. 

elongatus (greenstriped rockfish), S. 

helvomaculatus (rosethorn rockfish), 

S. proriger (redstripe rockfish), and S. 

zacentrus (sharpchin rockfish), particularly concerning their distribution, abundance, and life history parameters. These four species, plus S. 

alutus and S. polyspinis, are found in an 

overlapping geographic region (i.e., 

the Northeast Pacific), but vary with 

respect to distribution range (Orr et 

al., 2000; Love et al., 2002) and depth. 

In a study of Sebastes spp. assemblages 

(i.e., rockfish species captured during 

West Coast assessment surveys), Weinberg (1994) determined that several of 

these six species co-occur in distribution a significant amount of the time.

The above rockfish species, with the 

exception of S. alutus and S. polyspinis, 

have been lightly exploited in the 

past, but can be captured efficiently 

with bottom trawls. With declines in 

populations of other commercial fish 

species, their importance is growing 

as the fishing industry seeks new fishing opportunities. Landings of these 

four rockfish species have already begun to increase (Douglas, 1998; Dick 

and MacCall, 2010), and information 

on life history parameters is critical for their management. Currently 

these four rockfish species are managed with other Sebastes species under 

a “Sebastes complex” quota and listed 

variously as “small rockfish,” “other 

rockfish,” or “remaining” rockfish in 

the catch statistics.

The genus Sebastes is in the subfamily Sebastinae, and family Scorpaenidae (Kendall, 1991). Sebastes and the 

other three genera in the subfamily 

Sebastinae are all live-bearing (or viviparous), while most other genera in 

the family Scorpaenidae are oviparous 

(Takahashi et al., 1991). Fertilization 

occurs internally in Sebastes; embryos 

develop, hatch in the ovaries, and are 

extruded as larvae.

Our study suggests that oocyte development for each respective species is group synchronous, producing 

only one brood per year (Asturiano 

et al., 2002), although there is evidence to indicate that under certain 

environmental conditions and food 
2 Professional Paper NMFS 14

availability, some species (i.e., S. elongatus) are capable 

of producing multiple broods (Love et al., 1990). After 

ovarian recrudescence is well underway, two modes of 

oocytes are found: one mode at resting stage and one 

progressing synchronously through vitellogenesis or 

maturation. In Sebastes there is a delay between copulation and oocyte fertilization during which sperm is 

stored in the inter-lamellar tissues of a mature ovary 

(Moser, 1967a). As a result, the reproductive development of males and females is asynchronous temporally. 

The mating season precedes the maturation of the 

oocytes, imposing a need for sperm storage. Copulation 

can precede oocyte maturation by as long as six months 

(Moser, 1967a, 1967b; Shaw, 1999). 

Research detailing sexual maturity in Sebastes has included a combination of several methods. A number of 

studies were limited to gross anatomical criteria for staging of the ovaries. Sometimes a gonadosomatic index 

was used as a measure of sexual maturity. Microscopic 

analysis and complete oocyte staging of rockfishes is 

often incomplete. Even less has been done to document sperm development in Sebastes. The presented 

observations will contribute to a better understanding 

of reproduction in this genus by providing additional 

and more detailed descriptions of this process. 

We present in this paper a histological scheme to 

divide the reproductive cycle of Sebastes into 11 phases 

of male reproductive development, with 10 stages of 

sperm development and 1 stage of spermatozoa atresia. 

Female reproductive development was divided into 12 

phases, with 10 stages of oocyte development, 1 stage 

of embryonic development, and 1 stage of oocyte 

atresia. Embryonic development up to parturition was 

divided into 33 stages. The developmental phases of all 

species reviewed in this histological study (S. alutus, S. 

elongatus, S. helvomaculatus, S. polyspinis, S. proriger, and 

S. zacentrus) followed the developmental classifications 

listed above. As a result, the proposed classifications may 

apply to all Sebastes species regardless of the number of 

broods produced per year; some species from Southern 

California and farther south have more than one brood 

per year (Moser, 1967b; Love et al., 1990). In this study, 

because of completeness of sample collection for some 

species, S. elongatus is the standard example for sperm 

development at the microscopic level, while S. proriger 

and S. alutus serve as similar standards for oocyte and 

embryological development, respectively. 

This study blended together existing information on 

rockfish life history parameters, examined existing data 

sets, and made special collections to fill data gaps to assemble a complete description of the life histories of the 

six targeted rockfish species. The mortality rates, age and 

size composition, depth and geographic distribution, 

food habits, and habitat requirements for four of these 

species were examined in order to determine if they 

can be managed as a group (Shaw, 1999; Shaw and 

Gunderson, 2006, 2008). All of this information is necessary to determine the productivity and resilience of 

these stocks. This information, along with responsible 

management, will enable long term exploitation of 

these species without endangering their populations or 

diminishing their role within their respective ecosystems. This atlas focuses only upon the reproductive 

biology of the above six rockfish species, while specific 

information addressing 50% maturity, age-length relationships, weight-length relationships, natural mortality, 

and total mortality for S. elongatus, S. helvomaculatus, S. 

proriger, and S. zacentrus can be found elsewhere (Shaw, 

1999; Shaw and Gunderson, 2006, 2008).

Materials and methods

Collections at the rate of 15 specimens per species per 

month were targeted from January to October 1995 

from commercial catches for S. elongatus (n=123), S. 

helvomaculatus (n=82), S. proriger (n=115), and S. zacentrus (n=124) landed at Astoria, OR. Under the collection scenario for these four species, fish were captured 

in bottom trawls at locations within a few hours travel 

from Astoria (near the mouth of the Columbia River). 

Specimens of S. alutus (n=172) and S. polyspinis (n=323) 

were collected primarily by fisheries observers aboard 

commercial trawlers, but also by Alaska Fisheries Science Center personnel on research cruises in Alaska 

waters from October 2003 to March 2004. Physical data 

collected at the time of capture included fork length 

to the nearest millimeter, somatic weight to the nearest 

gram, and gonad weight to the nearest tenth of gram; 

maturity stage of both male and female fish was visually 

determined. A total of 939 gonads were collected.

Both gonads (ovaries and testes) were excised whole 

from fish. Depending upon the mass of the gonad, several small incisions were made throughout the gonad. 

The incisions were intended to allow more rapid and 

thorough penetration of fixative into the gonad, without severely damaging the integrity of the gonad or 

excessive loss of representative gonadal cells. A label 

was prepared containing species, sex, size, haul number, 

and location (unless specimen and catch position data 

was proprietary information, as is the nature of fisheries 

observer data). The label and entire gonad were then 

placed in linen bags and preserved in 10% formalin 

buffered with sodium acetate trihydrate.

At the laboratory, small longitudinal cross-sections 

encompassing the anterior, middle, and posterior portion of the ovaries and testes were taken to ensure organ 

homogeneity. A small segment (0.5 × 0.5 × 1.0 cm3) of 

tissue was excised from the center portion of each section of organ sampled. Tissue sections were prepared 
3

for histological examination as noted by Sheehan and 

Hrapchak (1980). In brief, tissues were thin-sectioned 

with a rotary microtome to a thickness of 5 μm and 

placed on glass slides. Sections were de-paraffinized, 

passed through a graded ethanol series, stained with 

Harris’ haematoxylin and eosin (H&E), and cover 

slipped. All slides were read blind, that is without prior 

knowledge of species, sex, size, or maturity. 

Hematoxylin and eosin are stains routinely used 

within a histology laboratory. Hematoxylin possesses 

a deep blue-purple color and stains nucleic acids (i.e., 

DNA, RNA) and other acidic compounds by a complex 

reaction that is not entirely understood. Eosin is pink, 

and stains proteins and other basic compounds nonspecifically and to varying degrees of intensity. In typical H&E stained tissue, nuclei are stained blue and the 

cytoplasm and extracellular matrix have varying degrees 

of pink staining. Not surprisingly, depending upon the 

state of the cell, the bluish nature or content of cells can 

vary considerably as RNA may be abundant within the 

cytoplasm of immature cells.

The size of the most advanced oocyte was used as 

a measure of ovary development (Clark, 1934). The 

diameter of the fifth largest oocyte in a random cross 

section from the middle portion of each ovary was used 

to represent the most advanced mode. Several investigators have used the diameter of the largest single oocyte to 

represent the most advanced mode (Yuen, 1955; Bunag, 

1956; Otsu and Uchida, 1959). West (1990) reported 

that in unpublished studies at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) 

Marine Laboratories on the threadfin bream (Nemipterus 

furcosus), correlation to the most advanced mode was improved from 0.97 to 0.99 (P<0.01) when the fifth largest 

oocyte was used, rather than the largest. This eliminated 

the situation where the largest oocyte might be an outlier 

from the distribution. In his comprehensive review of 

methods of assessing ovarian development, West (1990) 

found “little point in using measures more complicated 

than maximum (largest) oocyte diameter.”

Oocyte and embryo diameters were measured from 

histological cross sections, using an ocular micrometer 

and compound microscope. If embryos were present 

in the ovary or if embryos had hatched, an estimated 

standard length of the larvae was calculated using image 

analysis software.

Morphological observations

Collections of S. elongatus, S. helvomaculatus, S. proriger, 

and S. zacentrus were well distributed across all sizes, 

representing late immature to mature phases for both 

males and females. Collections of Sebastes alutus and S. 

polyspinis were not sufficiently distributed to provide 

a good overview of gonad development for these two 

species. The large majority of collections were of mature 

females harboring embryos and mature males postspawning. As a result, S. alutus was used as the “model” 

for embryonic development. Small numbers of representatives of other developmental phases were collected 

that permitted general agreement with similar gonad 

developmental phases with the other four species.

Gonadal development of these six species was similar 

to that reported for most other northern species of 

Sebastes (Moser, 1967a, 1967b; Leaman, 1988; Nichol, 

1990; Takahashi et al., 1991; McDermott, 1994). Under 

the sampling scheme in this study, reproductive development is generally group-synchronous, producing only 

one brood per year. However, under different environmental conditions, S. elongatus is capable of producing 

multiple broods (Love et al., 1990). After ovary recrudescence was well underway, two modes of oocyte stages 

were found, one mode at resting or pre-vitellogenic 

stages and one synchronized at a vitellogenic or maturation stage. The indices of gonadal development (GSI, 

ovary phase, and oocyte diameter in females; GSI and 

testis phase in males) produced similar results except 

that the peak in the GSI was slightly earlier than the other 

indices (see Table 1). This was due to the release of spermatozoa or embryos as the spawning season progressed.

The reproductive development of males and females 

is offset temporally (e.g., male gonad development anticipates female development). As a result, the mating 

season precedes the maturation of the oocytes, imposing a need for sperm storage (Fig. 17), while increasing 

the probability that spermatozoa will be available when 

oocyte maturation has occurred. Copulation preceded 

oocyte maturation by a minimum of one month in S. 

helvomaculatus to as long as six months in S. proriger. 

Parturition occurs in the late spring for four of the six 

examined species (Table 1).

We prefer to use the term “phase,” as opposed to 

“class,” to describe visual reproductive organ development and its aligned microscopic features because 

the term implies transition and not rigid categories. 

Indeed, a phase may be represented by several cell 

stages. The term “stage” is used to identify cellular development within both male and female reproductive 

organs, while the term “interval” refers to a group of 

related stages within an organ phase. Using this terminology, gross developmental phases of the ovary (5) 

and testes (4) were fewer in number than histological 

phases and therefore less precise in reflecting gonad 

status. Visual accuracy was also a problem. Immature 

phases were often difficult to differentiate from late 

spent or resting phases in both sexes, and misclassifications sometimes occurred. To assess maturity without 

histological confirmation, gross observations should be 

made during the mating season (late fall to winter) for 
4 Professional Paper NMFS 14

males and at the time of parturition (late spring) for 

females since no misclassifications were made of fish 

sampled at these times.

Finally, we wish to emphasize that inconsistent terminology presents complications in describing fish reproductive development as evidenced in a recent paper 

by Brown-Peterson et al. (2011). We have adopted the 

general terminology and organ development convention of Brown-Peterson et al. (2011) and Parenti and 

Grier (2004) in this atlas although we recognize the current momentum to use higher vertebrate terminology 

in describing fish germ cells in spermatogenesis and 

Table 1

Summary of life history parameters for Sebastes elongatus, S. helvomaculatus, S. proriger, and S. zacentrus. Similar data not 

available for S. polyspinis. Similar data for S. alutus can be found in Haldorson and Love (1991). Data for S. elongatus and S. 

helvomaculatus presented with permission from Shaw and Gunderson (2006, 2008).

elongatus helvomaculatus proriger zacentrus

Parameter ♂	 ♀	 ♂	 ♀	 ♂	 ♀	 ♂	 ♀

Max. age1 45 46 64 61 34 28 30 41

Max. length2 430 400 400 376 440 520 450 420

Max. weight3 980 915 910 760 1060 1700 1130 1035

L∞ (Wetherall)4 324 378 292 300 334 377 291 367

L∞ (Bertalanffy)5 301 375 279 287 295 383 269 332

K6 0.11 0.08 0.11 0.10 0.22 0.16 0.20 0.17

t

0

7 –3.27 –3.45 –2.07 –2.78 -0.72 –0.79 –0.81 –0.68

L0.5

8 230 210 228 208 243 262 209 223

A0.5

9 10 7 13 10 7 7 7 6

M1

10 0.10 0.10 0.07 0.07 0.13 0.16 0.15 0.11

M2

11 0.10 0.12 0.04 0.05 0.10 0.17 0.14 0.12

M3

12 0.15 0.04 0.13 0.12

Z13 0.43 0.31 0.35 0.39 0.95 0.62 0.70 0.73

GSI14 0.8 8.3 0.6 2.3 1.1 7.3 0.9 6.6

Mating15 Dec–Feb Dec–Apr Nov–Jan Oct–Jan

Parturition16 June May–Jun June Apr–May

Gestation17 40–50 40–60 35–50 40–60

Max. depth18 491 549 425 444

Mean depth19 158 219 156 207

Range north20 59°52′N 59°38′N 59°59′N 59°59′N

Range south21 28°10′N 32°34′N 32°43′N 32°46′N

1

Maximum age in years.

2

Maximum fork length in mm.

3

Maximum weight in grams.

4

Theoretical maximum length in mm calculated from Wetherall plot.

5

Theoretical maximum length in mm calculated from von Bertalanffy growth model.

6

Von Bertalanffy growth coefficient.

7

Theoretical age in years at zero length calculated from von Bertalanffy growth coefficient.

8

Von Bertalanffy estimated length in mm at 50% maturity.

9

Von Bertalanffy estimated age in years at 50% maturity.

10Hoenig maximum age based estimated mortality rate.

11estimated mortality rate from catch data.

12estimated mortality rate from calculated gonadosomatic index (GSI).

13Wetherall estimated total mortality.

14Gonadosomatic index.

15Period of mating.

16Spawning period.

17Gestation period in days.

18Maximum depth distribution in m.

19Mean depth of distribution.

20Northern range of distribution.

21Southern range of distribution.
5

oogenesis (Lubzens et al., 2010; Schultz et al., 2010). 

Citing previous research, these studies have done 

much to standardize terminology by careful description of cell morphology and function. For example, 

the term “lobule boundary cell” is no longer a valid 

term as considerable confusion existed in the location 

and function of this cell-type (Grier, 1993; Schulz et 

al., 2010). Furthermore, the testis appears to be of the 

unrestricted lobular type as defined by Grier (1993).

Testis development

The Sebastes testes are paired, elongate structures 

suspended dorsally in the posterior portion of the 

peritoneal cavity by a mesorchium. The two lobes of 

the testis are solid in appearance and equal in size, 

and cross-sections are roughly triangular except at the 

anterior and posterior ends. The efferent ducts of each 

lobe empty posteriorly and fuse to form a common 

seminal duct, which continues posteriorly between the 

urinary tract and intestine. It communicates exteriorly 

through a pore in the tip of the urogenital papilla.

Spermatogenesis is the transformation of primary 

spermatogonia into mobile spermatozoa through a 

series of cell divisions, both meiotic and mitotic. In 

the adult testis spermatogonial cysts develop along the 

entire length of the lobule. The cells within a cyst are 

derived from a single spermatogonium and thus represent a clone that develops synchronously (Schultz et 

al., 2010). However, within a lobule, spermatogonial 

cysts may develop asynchronously. Spermatocytes are 

formed as the spermatogonia enter meiotic prophase; 

spermatids are the result of the second meiotic division, and spermatozoa result from reorganization of 

the nucleus and cytoplasm and the formation of the 

flagellum. Spermatogenesis is dvided into 10 stages 

of cellular development following Carrillo and Zanuy 

(1977) and Gordo (1995) for stages of spermatogonia, 

and Agarwal (1996) with slight modification (spermatid and spermatozoa stages were split into early and 

late stages for each) for the remaining spermatogenesis stages.

Spermatogonia

Stage i: 1° spermatogonia (8–11 μm)

Primary spermatogonia (Ga) are the largest and 

most segregated among the spermatogenic cells. They 

possess a large, round, light-staining nucleus with a 

prominent nucleolus and chromatin threads. The 

cytoplasm has a weak affinity for basic dyes. They are 

found in higher concentration on the periphery of the 

testis and near the lobular wall, which is lined by Sertoli 

cells. All stages of spermatogonia have a diploid set of 

chromosomes.

Stage ii: 2° spermatogonia (6–8 μm) (Fig. 1)

Secondary spermatogonia (Gb) are derived from dividing primary spermatogonia and are found in small 

groups. The nucleus shows moderate staining with visible chromatin threads. They possess a large nucleus to 

cytoplasm ratio.

Stage iii: 3° spermatogonia (4–6 μm) (Fig. 2)

Tertiary spermatogonia (Gc) possess a condensed nucleus that stains dark due to the increasing density of the 

chromatin. They possess a reduced nuclear to cytoplasm 

ratio and are found in larger numbers than secondary 

spermatogonia within the Sertoli cell lined cysts.

Stage iv: 4° spermatogonia (2.5–4 μm) (Fig. 3)

Quaternary spermatogonia (Gd) have a more condensed nucleus with less cytoplasm and are found in 

even larger groups than the previous stage. 

Spermatocytes

Stage v: 1° spermatocytes (3–4.5 μm) (Fig. 4)

A short growth phase follows a quiescent period that 

gives rise directly to primary spermatocytes (PSc). A 

series of nuclear transformations (meiotic prophase) 

signals the first meiotic division. Cells possess a large 

basophilic nucleus and a large nucleus to cytoplasm 

ratio.

Stage vi: 2° spermatocytes (2–2.5 μm) (Fig. 5)

Each primary spermatocyte undergoes the first meiotic, or reduction, division and produces two daughter 

cells called secondary spermatocytes (SSc). These cells 

are very round and have a dark-staining nucleus but 

have a smaller nucleus to cytoplasm ratio than the previous stage.

Spermatids

Stage vii: early spermatids (2 μm) (Fig. 6)

The secondary spermatocytes undergo a second meiotic division, which gives rise to early spermatids (ESd) 

that now have a haploid set of chromosomes. In early 

spermatids the cytoplasm is difficult to see and the 

dark-staining nucleus is found in the periphery of the 

cell. The nucleus has a half moon shape early in this 

stage and later becomes crescent-shaped, which covers more than 180° of the circumference of the round 

cell.

Stage viii: late spermatids (2–2.5 μm) (Fig. 7)

In late spermatids (LSd) the crescent-shaped nucleus 

straightens to become more fusiform. This causes the 

shape of the cell to change from round to oval. The cell 

wall subsequently disappears.
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Spermatozoa

Stage ix: early spermatozoa (10–12 μm including the 

flagellum) (Fig. 8) 

Spermatids undergo a process of differentiation, giving rise to the mobile spermatozoa. Early spermatozoa 

(ESz) possess a long flagellum with a long pyriformshaped nucleus (~3 μm in length and 1 μm in diameter) 

that are deeply staining but remain within cysts of the 

seminiferous tubule, with their heads embedded in the 

Sertoli cells.

Stage x: late spermatozoa (10–12 μm including 

the flagellum) (Fig. 9) 

Late spermatozoa (LSz) are free of the cyst and begin 

to migrate into the tubule lumen of the spermatic duct, 

free from the Sertoli cells.

Atresia

Stage α: residual spermatozoa (Figs. 10 and 11)

Some spermatozoa remain in some lobules after 

spawning. Sertoli cells are often observed attached to or 

with engulfed residual spermatozoa (RSz), demonstrating their important role in resorption or phagocytosis 

of residual spermatozoa.

Testis phases

Ten testis development phases and one atresia phase 

(i.e., organ development that may contain several sperm 

cell types or stages) closely parallel spermatocyte stages 

(i.e., specific cellular development of testicular cells). 

Each phase is defined as beginning with the first appearance of the same stage spermatocyte and ending with 

the first appearance of the next stage spermatocyte in 

the testis as a whole. The ten development phases are 

followed by one atresia (or spent) phase. The various 

phases will be illustrated in the figures with sections 

from S. elongatus testes.

Phase I: 1° spermatogonia

No testes were found in this phase even though fish 

as small as 210 mm and testis that weighed less than 1 g 

were examined.

Phase II: 2° spermatogonia (Fig. 1)

Testes in this phase retained primary and secondary 

spermatogonia. Figure 1 illustrates a testis in this phase 

from a fish that has never spawned. Testes of this phase 

are considered immature unless there is evidence of 

residual spermatozoa (RSz). Sperm cells in mature 

testes progress past the secondary spermatogonia stage 

before all the RSz are resorbed.

Phase III: 3° spermatogonia (Fig. 2)

Phase III testes possess primary, secondary, and 

tertiary spermatogonia. Primary spermatogonia stain 

the weakest and are found singularly. Secondary spermatogonia are found in groups of 3–5, while tertiary 

spermatogonia are found in groups of 10–20 per cyst 

and stain the darkest with H&E stain.

Phase IV: 4° spermatogonia (Fig. 3)

All four stages of spermatogonia are contained in 

testes of this phase. Quaternary spermatogonia stain 

the darkest of the spermatogonia. The population of 

quaternary spermatogonia in each cyst is about twice 

that of tertiary spermatogonia, although actual counts 

are difficult. This was due to the combination of the 

shrinking size of the spermatogonia and the 3-dimensional nature of the cysts, where the 2-dimensional 

section does not reveal all of the spermatogonia within 

each cyst.

Phase V: 1° spermatocytes (Fig. 4)

Testes in this phase contain all four stages of spermatogonia plus the primary spermatocyte. Stained testes sections (H&E) have a noticeably darker appearance 

as the sperm cells begin to dominate.

Phase VI: 2° spermatocytes (Fig. 5)

Secondary spermatocytes are very round, dark, and 

about twice as numerous per cyst as the primary spermatocytes. This phase of testis development contains 

primary spermatogonia and sometimes other stages of 

spermatogonia.

Phase VII: early spermatids (Fig. 6)

This phase of testes stains very dark with H&E, with 

early spermatids and secondary spermatocytes dominating. Primary spermatogonia and other stages of 

spermatogonia are diminished in number and take on 

the role of the “reserve fund.” 

Phase VIII: late spermatids (Fig. 7)

Nearly all the cysts have developed past the secondary 

spermatocyte stage. The crescent-shaped early spermatids and the “pancaking” late spermatids dominate. Very 

few spermatogonia are noticeable.

Phase IX: early spermatozoa (Fig. 8)

The pink to light red flagella (Flag) (H&E stain) make 

their appearance at the center of the cyst with the heads 

of the early spermatozoa oriented to the perimeter. 
7

Early and late spermatids and early spermatozoa are 

numerous while spermatogonia stages become rare.

Phase X: late spermatozoa (Fig. 9)

At this testis phase, all sperm cells within the cyst have 

arrived at the late spermatozoa stage. A few primary 

spermatogonia can be found among the cyst lining 

Sertoli cells. Late spermatozoa have moved into the 

efferent ductules and the spermatic duct. Here, they 

accumulate until mating occurs.

Phase XI: residual spermatozoa (Figs. 10 and 11)

Spermatogenesis occurs within the stoma (epithelium) of seminiferous tubules and as spermatogenesis 

progresses, that epithelium becomes attenuated (e.g., 

becomes shorter in height), yielding to the increasing number of developing spermatozoa. Eventually, 

the once robust cuboidal Sertoli cells become shorter 

in height as the mature and profuse spermatozoa fill 

the lumen. After mating and release of mature spermatozoa, the tubular epithelium of the seminiferous 

tubules begins a recovery process.

In this phase of the testes, the dark spermatozoa give 

way to the recovering Sertoli cells and interstitial tissue. 

A few pockets of residual spermatozoa can be found, 

often in the process of resorption which is generally 

facilitated by the Sertoli cells.

Table 2

Summary of the gross and histological phases and cell stages of testes in Sebastes. Table partially reproduced and with 

permission from Shaw and Gunderson (2006, 2008).

Gross testes phase Histological testes phase Sperm cell stages present

Immature I, II Ga,Gb

Developing III, IV, V, VI, VII, VIII, IX Ga, Gb, Gc, Gd, PSc, SSc, ESd, LSd, ESz

Ripe X Ga, ESz, LSz

Spent XI RSz, LSz, PSc, SSc

Regenerating XI, II, III, IV RSz, Ga, Gb, Gc, Gd

Gross morphological phases of the testes

Immature: Testes are small, translucent, and string-like, 

with sharp edges. No milt is present.

Developing: Testes are larger and opaque; milt is present.

Ripe: Testes are large and white in color. Milt is present in the rounded cross section and can be expressed 

with pressure to the abdominal cavity at the peak of 

this phase.

Spent: Testes are brown to gray in color, small and flaccid. No milt is present.

Regenerating: Testes become firm as the organ increases in mass, and become triangular in shape and 

translucent on the periphery.

In the field, visual examination of testis maturity provides an on-site, but potentially inaccurate, diagnosis of 

gonad development. Histological or microscopic analysis provides a more accurate and complete description 

of testis development, but is not as rapid. Comparison of 

the two methods is provided in Table 2, which summarizes tissue and cellular features associated with visually 

described testis development.
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Figure 1

Phase II testes (secondary spermatogonia phase) of a 254 mm Sebastes elongatus with primary and 

secondary spermatogonia. Collected 10 June 1995. (A) 235× and (B) 2000×.
9

Figure 2

Phase III testes (tertiary spermatogonia phase) of a 266 mm Sebastes elongatus with primary, 

secondary, and tertiary spermatogonia. Collected 15 July 1995. (A) 235× and (B) 2000×.
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Figure 3

Phase IV testes (quaternary spermatogonia phase) of a 261 mm Sebastes elongatus with primary, 

secondary, tertiary, and quaternary spermatogonia. Collected 15 July 1995. (A) 235× and (B) 2000×.
11

Figure 4

Phase V testes (primary spermatocyte phase) of a 279 mm Sebastes elongatus with primary, tertiary, 

and quaternary spermatogonia, and primary spermatocytes. Collected 18 August 1995. (A) 235×

and (B) 2000×.
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Figure 5

Phase VI testes (secondary spermatocyte phase) of a 293 mm Sebastes elongatus with primary and 

tertiary spermatogonia, and primary and secondary spermatocytes. Collected 18 August 1995. 

(A) 235× and (B) 2000×.
13

Figure 6

Phase VII testes (early spermatid phase) of a 326 mm Sebastes elongatus with primary and tertiary 

spermatogonia, secondary spermatocytes, and early spermatids. Collected 23 September 1995. 

(A) 235× and (B) 2000×.
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Figure 7

Phase VIII (late spermatid phase) of a 219 mm Sebastes elongatus with secondary spermatocytes, and 

early and late spermatids. Collected 23 November 1995. (A) 235× and (B) 2000×.
15

Figure 8

Phase IX testes (early spermatozoa phase) of a 294 mm Sebastes elongatus with late spermatids and 

early spermatozoa. Collected 16 December 1995. (A) 235× and (B) 2000×.
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Figure 9

Phase X testes (late spermatozoa phase) of a 278 mm Sebastes elongatus with late spermatozoa. 

Collected 28 February 1995. (A) 235× and (B) 2000×.
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Figure 10

Early phase XI testes (residual spermatozoa phase) of a 338 mm Sebastes elongatus with residual 

spermatozoa and primary spermatogonia. Collected 20 April 1995. (A) 235× and (B) 2000×.
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Figure 11

Late phase XI testes (residual spermatozoa phase) of a 237 mm Sebastes elongatus with residual 

spermatozoa, and primary, secondary, and tertiary spermatogonia. Collected 10 June 1995. 

(A) 235× and (B) 2000×.
19

Ovary development

The Sebastes ovary is attached dorsally and is a paired, 

elongate structure suspended in the posterior portion 

of the peritoneal cavity. Each lobe of the ovary is a thinwalled, sac-like structure that is tapered posteriorly 

and fuses with the other lobe to form a single oviduct. 

The oviduct extends ventrally between the urinary 

tract and intestine; the most posterior portion forms 

the genital opening which is located posterior to the 

anus and anterior to the urinary opening (Moser, 

1967a).

Oogenesis is the transformation of oogonial cells 

into oocytes through a series of cell divisions, with associated cytoplasmic and chromosomal changes. In the 

adult ovary, oogonia continue to divide and multiply 

by ordinary mitosis. Oocytes are formed from oogonia 

via meiosis which is arrested at the first prophase and 

second metaphase stages. The development of the oocytes was divided into ten stages based on the scheme 

first used by Yamamoto (1956) for the flounder 

(Liopsetta obscura), with one additional stage and other 

minor modifications for use in the viviparous Sebastes. 

Figures 12–14 are presented to illustrate comparative 

sizes of developing oocytes. Specific oocyte features 

as discussed in relation to Figures 12–14 and associated with ovarian development are depicted in Figs. 

15–24.

Oogonia

Stage 0: oogonia (8–10 μm) (Fig. 12)

These are very small, round germ cells still capable 

of mitotic division and usually found in nests in the 

epithelium of the ovarian lamellae. Each oogonium 

has a thin layer of clear cytoplasm and a relatively large 

nucleus, which stains lightly with H&E. In the center of 

the nucleus is a single large nucleolus.

First growth interval

Stage i: chromatin nucleolus (10–20 μm) (Fig. 12)

These are small oocytes with a nucleus now surrounded by a thin layer of weakly staining (blue) cytoplasm. 

The nucleus still contains a single large nucleolus, but is 

now encircled by prominent chromatin threads.

Stage ii: early perinucleus (25–70 μm) (Fig. 12)

Oocyte size increases as the nucleus grows and the 

cytoplasm thickens. From this point forward the enlarging nucleus is sometimes referred to as the “germinal 

vesicle.” The cytoplasm is basophilic, staining a very 

dark blue, and is uniform. Many oocytes at this stage 

are polyhedral in shape. There is one relatively large 

nucleolus with several smaller nucleoli developing 

around the periphery of the nucleus. A thin layer of 

follicle cells begins to form around the oocyte against 

the zona radiata.

Stage iii: late perinucleus (60–130 μm) (Fig. 12)

The oocyte continues to grow in diameter and becomes more rounded. The cytoplasm is still basophilic 

but does not stain as deeply and is sometimes zoned 

(peripherally located as a result of yolk accumulation). The nucleoli become more numerous and uniform in size along the periphery of the nucleus, and 

lampbrush chromosomes become apparent. This is 

the end of meiotic prophase and the most advanced 

stage of oocyte growth that is present throughout 

the year. Oocytes in this stage are sometimes termed 

“resting oocytes.” The chromosomes of the resting 

oocytes become arrested at late diplotene of the first 

meiotic division (Tokarz, 1978). The Balbiani body or 

yolk nucleus, which contains a number of cytoplasmic 

organelles including mitochondria, Golgi bodies, and 

endoplasmic reticulum, (Guaraya, 1979) is formed at 

this stage.

Second growth interval

Stage iv: oil vacuole (110–190 μm) (Fig. 13)

In the second growth interval, the shape of the oocyte is more spherical. Transparent oil vacuoles begin 

to form in the perinuclear cytoplasm. In the nucleus, 

lampbrush chromosomes are often visible (see Fig. 13-

iv). The follicle is thickened and is composed of a layer 

of nucleated cells (granulosa) and a thin layer of connective tissue to the exterior (see Fig. 17). Most other 

teleosts would start forming cortical alveoli (or yolk 

vesicles) in the cortical cytoplasm at this stage but they 

are notably lacking or at least much less prominent in 

Sebastes. Hence, we propose the new name “oil vacuole” 

for this stage in Sebastes, which is equivalent to the “yolk 

vesicle stage” in Yamamoto (1956).

Stage v: 1° yolk (165–240 μm) (Fig. 13) 

Vitellogenesis begins at this stage with the appearance 

of eosinophilic yolk granules in the cortical cytoplasm 

(see Fig. 19). As this stage progresses, the yolk granules begin to move centripetally from the periphery of 

the cytoplasm and the oil vacuoles move centrifugally 

from the perinuclear cytoplasm.

Stage vi: 2° yolk (200–265 μm) (Fig. 13)

At this stage the yolk granules increase in number 

and coalesce into yolk globules. The oil vacuoles also 

increase in size and number. As both the yolk droplets 

and oil vacuoles continue to proliferate, they fill their 

respective spaces in the cytoplasm until they meet and 

form two layers (or rings) against each other.
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Stage vii: 3° yolk (230–350 μm) (Fig. 13) 

Oil vacuoles and yolk globules are no longer segregated 

and completely fill the cytoplasm in a randomly dispersed 

pattern. The nonstaining oil vacuoles are much larger 

than the variably, eosinophilic stained yolk globules. 

The zona radiata has increased in thickness to 5–7 μm.

Oocyte maturation interval

Stage viii: migratory nucleus (325–670 μm) (Fig. 14) 

Meiosis resumes at this stage as the nucleus moves 

from the center of the cell towards the periphery of 

the cell and the micropyle. The oil vacuole begins to 

coalesce into a large vacuole, occupying the area that 

the nucleus has vacated. The follicle has stretched and 

thinned due to the rapid growth of the oocytes. Lampbrush chromosomes are visible at this stage.

Stage ix: prematuration (440–710 μm) (Fig. 14) 

The nuclear membrane dissolves and the nucleus begins to disappear, more oil coalesces from the vacuoles 

into the central oil vacuole, and the yolk globules begin 

to coalesce into a yolk mass surrounding the oil vacuole. 

The walls of the granulosa cells disappear, leaving a 

single cell with many nuclei or a syncytial arrangement.

Stage x: mature (540–725 μm) (Fig. 14) 

When the nucleus has disappeared, the oocyte can be 

classified as mature (Wasserman and Smith, 1978). The 

yolk mass (now completely coalesced and transparent 

pink in H&E stain) surrounds the oil vacuole which is 

near the periphery of the cell and clear in color.

Ovary phases

Twelve histological development phases closely parallel 

the developmental stages of individual oocytes. Each 

phase is defined as beginning with the first appearance of the same stage oocyte and ending with the first 

appearance of the next stage oocyte in the ovary as a 

whole. The ovary development phases are followed by 

embryonic development and atresia (or spent) phases. 

The various phases are illustrated in Figs. 15–24 with 

sections from S. proriger ovaries.

Phase I: chromatin nucleoli and Phase II: early perinucleus 

Ovaries from fish as small as 120 mm were collected 

and all had some oocytes that had developed past the 

early perinucleus stage. Thus, no ovary with less development than the late perinucleus phase (III) was 

encountered.

Phase III: late perinucleus (Fig. 15) 

Ovaries in this phase contain oogonia, chromatin 

nucleoli, early perinucleus, and late perinucleus oocytes. 

The oogonia and chromatin nucleoli stages are found 

in oogonial nests. As the late perinucleus stage oocytes 

grow, they are found less clustered, with space for 

substantial growth during vitellogenesis. Spawning has 

occurred previously in the ovary in Fig. 15, as evidenced 

by the remnants of a post-ovulatory follicle.

Phase IV: oil vacuole (Fig. 16)

The oil vacuole phase has all the oocyte stages of the 

previous phase plus the oil vacuole stage. The growing 

oocytes are beginning to grow synchronously, but the 

oogonial nests are still prominent.

Phase V: 1° yolk (Fig. 17)

Primary yolk phase ovaries may include all the oocyte 

stages of the previous phases plus the primary yolk 

stage signaling the onset of vitellogenesis. Spermatozoa 

are stored in the interstitial tissue of a primary yolk 

phase ovary awaiting the maturation of the oocyte. At 

this point, the spermatozoa have lost their flagella.

Phase VI: 2° yolk (Fig. 18)

In this ovary phase two distinct modes of oocytes 

have begun to emerge. The mode in first growth phase 

(Og-LPN) is arrested at the late perinucleus stage 

and is sometimes called the “reserve fund,” while the 

mode at the secondary yolk stage progresses in a synchronized manner through the second growth phase 

(vitellogenesis).

Phase VII: 3° yolk (Fig. 19)

This ovary phase, like the previous one, has two modes 

of oocyte development. The first is still the first growth 

phase oocytes, which occasionally include an oil vacuole 

stage oocyte. The second mode has now progressed to 

the tertiary yolk stage.

Phase VIII: migratory nucleus (Fig. 20)

The second mode has now progressed to the migratory nucleus stage oocyte. The nuclear membrane has 

disappeared. An occasional atretic vitellogenic oocyte 

is seen.

Phase IX: prematuration (Fig. 21)

The first growth stage of oocytes is still found in this 

ovarian phase but is now dwarfed by the increasing size 

of prematuration oocytes.

Phase X: mature (Fig. 22)

The interstitial tissue surrounding the mature oocyte 

is becoming sparse, even though oogonial nests can 

still be found in the interstitial tissue. Ovulation begins 

when the oocytes have matured, the stored spermatozoa are released, and fertilization commences.
21

Phase XI: embryonic development (Fig. 23) 

Embryos develop synchronously through the 33 

embryonic stages within the ovary and hatch before 

parturition. Embryos in Fig. 23 are at stage 33 (hatched, 

preborn larvae).

Phase XII: atresia (Fig. 24) 

Oocytes that have failed to mature and residual 

embryos, which remain unborn after parturition has 

ceased, are found in various atretic states at this phase. 

Postovulatory follicles that have not yet collapsed and 

are undergoing atresia are seen in individuals that have 

recently undergone parturition.

Gross morphological phases of the ovary

Immature: Ovaries are small and no oocytes are visible. 

The color is translucent pink and no dark spots or 

blotches are present.

Vitellogenesis: Ovaries are enlarging and are opaque 

pink to yellow in color. The small oocytes are now discernible and opaque.

Clear egg: The eggs are now mature, large, translucent, 

and yellow. Ovulation and fertilization occur early in 

this stage so most eggs in this stage have been fertilized. 

The ovary wall is thin and flaccid.

Eyed larvae: Black pigmentation in the larvae eyes impart a grey color to the ovary which is less translucent 

than the previous stage. The ovary wall is fragile.

Spent: The ovary is flaccid and nearly empty. Residual 

larvae are often present and are seen as dark spots 

against a purple background.

Regenerating: Few residual larvae may be present. Organ is reduced in size but undergoing reorganization of 

muscle, blood vessels, and ovarian wall. Becoming firm 

in comparison to a spent organ.

As previously noted for the testis, field visual examination of ovary maturity provides an on-site, but potentially 

inaccurate, diagnosis of gonad development. Histological or microscopic analysis provides a more accurate and 

complete description of ovarian development, but is not 

as rapid. Comparison of the two methods is provided in 

Table 3 which summarizes tissue and cellular features 

associated with visually described ovary development.

Table 3

Summary of the gross and histological phases and cell stages of ovaries in Sebastes. Table partially reproduced with permission 

from Shaw and Gunderson (2006, 2008).

Gross ovary phase Histological ovary phase Oocyte cell stages present

Immature I,II,III Og, ON, CN, EPN, LPN

Vitellogenesis IV, V, VI, VII, VIII, IX Og, CN, EPN, LPN, OV, PY, SY, TY, MN, PM

Clear egg X,XI Og, CN, EPN, LPN, MO, Em, *

Eyed larvae XI Og, CN, EPN, LPN, Em, *

Spent XII REm, EF, Og, CN, EPN, LPN, OV, *

Regenerating II, III REm, Og, ON, *

*Atresia is potentially possible in all phases of ovarian development. In this study, atresia was rare as reported by de Bruin et al. (2004) and was infrequently 

encountered during Clear egg, Eyed larvae, Spent, and Regenerating ovarian phases. 
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Figure 12

Oogonium and first growth interval oocytes. Images on the left are standardized to about the same size for all 

stages. Images on the right are magnified to the same power (50×) to show relative sizes. Stages shown are (0) 

oogonium, (i) chromatin nucleolus, (ii) early perinucleolus, and (iii) late perinucleolus with Balbiani body 

(arrows).
23

Figure 13

Second growth interval oocytes. The images on the left are standardized to about the same size for 

all stages. The images on the right are magnified to the same power (50×). Stages shown are (iv) oil 

vacuole with lampbrush chromosomes (arrows), (v) 1° yolk, (vi) 2° yolk, and (vii) 3° yolk.
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Figure 14

Maturation interval oocytes. The images on the left are standardized to about the same size for all stages. 

The images on the right are magnified to the same power (50×). Stages shown are (viii) migratory 

nucleus, (ix) prematuration, and (x) mature.
25

Figure 15

Phase III ovary (late perinucleus phase) of a 320 mm Sebastes proriger with oogonia, chromatin nucleolus, 

early perinucleus, and late perinucleus stage oocytes. Collected 18 August 1995. (A) 100×, (B) 400×, 

and (C) 2000×.
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Figure 16

Phase IV ovary (oil vacuole phase) of a 318 mm Sebastes proriger with late perinucleus and oil vacuole 

stage oocytes. Collected 23 September 1995. (A) 100×, (B) 400×, and (C) 2000×.
27

Figure 17

Phase V ovary (primary yolk phase) of a 325 mm Sebastes proriger with early perinucleus, late perinucleus, 

and 1° yolk stage oocytes. Stored spermatozoa without flagella are also present in the interstitial tissue. 

Collected 23 November 1995. (A) 100×, (B) 400×, and (C) 2000×.
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Figure 18

Phase VI ovary (secondary yolk phase) of a 314 mm Sebastes proriger with early perinucleus, late 

perinucleus, 1° yolk, and 2° yolk stage oocytes. Collected 23 November 1995. (A) 100×, (B) 400×, and 

(C) 2000×.
29

Figure 19

Phase VII ovary (tertiary yolk phase) of a 328 mm Sebastes proriger with early perinucleus, late 

perinucleus, oil vacuole, and 3° yolk stage oocytes. Collected 16 December 1995. (A) 100×, (B) 400×, 

and (C) 2000×.
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Figure 20

Phase VIII ovary (migratory nucleus phase) of a 354 mm Sebastes proriger with migratory nucleus stage 

oocytes. Collected 28 February 1995. (A) 100×, (B) 400×, and (C) 2000×.
31

Figure 21

Phase IX ovary (prematuration phase) of a 300 mm Sebastes proriger with early perinucleus, late 

perinucleus, oil vacuole, and prematuration nucleus stage oocytes. Collected 20 April 1995. (A) 100×

and (B) 200×.
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Figure 22

Phase X ovary (mature phase) of a 322 mm Sebastes proriger with mature stage oocytes. Collected 9 May 

1995. (A) 100× and (B) 200×.
33

Figure 23

Phase XI ovary (embryonic phase) of a 345 mm Sebastes proriger with early perinucleus, late perinucleus, 

oil vacuole (early), eyed larvae, and empty follicles stages. Collected 10 June 1995. (A) 50×, (B) 100×, 

and (C) 400×.
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Figure 24

Phase XIII ovary (atresia phase) of a 323 mm Sebastes proriger with early perinucleolus, late perinucleolus, 

and empty follicles stages. Collected 15 July 1995. (A) 100×, (B) 400×, and (C) 2000×.
35

Embryonic development

The normal embryonic development for S. schlegeli

(N=33 stages) has been briefly described by Yamada 

and Kusakari (1991) following the embryonic model 

of Oppenheimer (1937) for Fundulus heteroclitus (N=34 

stages). Their description was based on a series of embryos gently suctioned from live females every 12 to 

15 days and examined macroscopically. The extracted 

tembryos were placed in saline solution in a petri dish 

and then observed and photographed under a dissecting 

microscope. Some early stage embryos were followed 

over time in the petri dish. In contrast, more comprehensive time-related accounts of normal embryonic 

stages are available for the zebrafish, Danio rerio (Kimmel et al., 1995) and medaka, Oryzias latipes (Iwamatsu, 

2011). In both instances, the time after fertilization is 

correlated with developmental stage and both provide 

“fill-in” observations and terms of reference in our description of rockfish embryonic development.

Embryonic development of the Sebastes species in this 

histological study closely tracks embryonic development 

as briefly described by Yamada and Kusakari (1991) for 

S. schlegeli, and which is supported by general observations on embryo development in yellowtail rockfish 

(S. flavidus, Bowers 1992), and grass (S. rastrelliger) and 

brown (S. auriculatus) rockfish (see Table 4; Chaillé, 

2006). In general, embryonic descriptions have previously been performed almost exclusively by macroscopic 

examination. Histological and ultrastructural descriptions are uncommon and rarely supported by parallel macroscopic studies. Bowers (1992) provided an 

abbreviated microscopic analysis on field collected 

specimens. Our study is solely dependent upon examination of histological sections that visually represented 

gross morphological phases of the ovary. Because our 

study is 2-dimensional as opposed to traditional 3-dimensional macroscopic analyses, not all stage features 

were observed in our study or were not observed at 

the specific stages noted by Yamada and Kusakari 

(1991). As a result, figures were occasionally selected 

that demonstrated representative organ development 

for approximate aged embryos (see Table 4). Regardless, our observations did appear to closely parallel 

the observations of Yamada and Kusakari (1991), but 

we also recommend reviewing the manuscripts by 

Kimmel et al. (1995) and Iwamatsu (2011) for detailed 

fish embryology.

Stage x: mature (540–725 μm) (Fig. 14x) 

When the nucleus has disappeared, the oocyte can be 

classified as mature (Wasserman and Smith, 1978). The 

yolk mass (now completely coalesced and transparent 

pink in H&E stain) surrounds the oil vacuole which is 

near the periphery of the cell and clear in color.

Stage 1: mature ovum (Fig. 25) 

An eosinophilic yolk (Y) mass makes up the majority of a mature unfertilized ovum, but it also contains 

a number of oil vacuoles (OV) which are clear and 

colorless.

Zygote period: a newly fertilized ovum, but prior to 

cleavage.

Stage 2: formation of blastodisc (Fig. 26) 

In stage 2 or the one-cell stage, the fertilized ovum 

is called a zygote and the blastodisc (Bd) or germinal 

disc appears on the surface of the yolk.

Cleavage period: a series of cell divisions that occur 

prior to formation of the blastula. The resulting cells 

are generally of equal size.

Stage 3: 2-celled embryo (Fig. 27) 

The first cleavage yields two cells or blastomeres 

(Bm), resulting in the 2-celled embryo. The cleavage 

furrow is oriented along the animal and vegetative 

poles. This and subsequent collections of blastomeres result in a blastoderm. As division progresses, 

mitotic figures (MF) may become evident (see Figure 

34B).

Stage 4: 4-celled embryo (Fig. 28) 

The two blastomeres visible in stage 3 undergo a 

subsequent cleavage, occurring at right angle to the 

first cleavage plane and resulting in four basophilic 

blastomeres easily distinguished from the pink staining eosinophilic yolk (Figure 28C). The four cells are 

arranged in a 2×2 array. Figure 28B appears to be in 

transition from a 4-celled embryo to an 8-celled embryo. From this point forward, the number and orientation of the blastomeres is less evident in histological 

sections. Thus, we rely upon the collective descriptions 

by Kimmel et al. (1995) and Iwamatsu (2011).

Stage 5: 8-celled embryo (Fig. 29)

A third cleavage plane develops in parallel to the first, 

dividing the four blastomeres into an 8-celled embryo. 

The cleavages cut the short axis, resulting in two rows 

of four cells.

Stage 6: 16-celled embryo (Fig. 30) 

The fourth cleavage plane that occurs parallel to the 

second cleavage results in a 16-celled embryo.

Stage 7: 32-celled embryo (Fig. 31) 

The fifth cleavage plane generally divides the marginal 12 blastomeres meridionally into 24. The central four blastomeres divide horizontally into eight 

blastomeres. During this stage an outer and inner layer 

are evident in the central region of the blastoderm. 
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Stage 7 exhibits presumed 32 blastomeres as a result of 

another cycle of cleavage.

Stage 8: 64-celled embryo (Fig. 32) 

After completion of the sixth cycle of cleavages the 

embryo possesses 64 blastomeres arranged in three 

layers. This stage has the first appearance of the outer 

enveloping layer (EVL) composed of the topmost 

layer of blastomeres of the blastoderm. From this stage 

forward, cell sizes may vary.

Blastula period: characterized by early metasynchronous cell cycles followed by asynchronous cell 

cycles, ending with the initiation of epiboly. Cells vary 

in size.

Stage 9: morula (Fig. 33) 

Yamada and Kusakari (1991) note that the morula 

stage occurs after the 64-cell embryo stage. However, 

the morula or mulberry stage in animals may occur as 

early as the 16-cell stage and as late as the 512-cell stage 

(Iwamatsu, 2011). In fish, the morula is characterized 

as a dome-shaped aggregate of blastomeres that have 

not yet started migrating over the yolk of the embryo 

or progressing into the blastula stages. Cleavage planes 

vary depending upon the position of the blastomere 

within the raised, oval, basophilic blastoderm. At about 

512 blastomeres, the yolk syncytial layer (YSL) forms 

(Fig. 36). More current fish development publications 

abstain from using the term “morula.” We continue 

to use the term as a means of connection to previous 

literature only.

Stage 10: early blastula (Fig. 34)

The dome-shaped blastoderm is composed of approximately 1000 cells with the inner cells being smaller 

than the outer blastomeres.

Stage 11: late blastula (Fig. 35)

Blastomeres begin to project into the yolk mass, but 

the blastoderm is still dome-shaped.

Stage 12: beginning of epiboly (Fig. 36)

The dome shape of the blastoderm begins to flatten as 

blastomeres migrate over the periphery of the yolk. The 

yolk syncytial layers (YSL) form earlier, but it is evident 

in this figure.

Gastrula period: cellular reconstruction of the blastoderm resulting in a three germ-layered structure (organ 

anlage) and ending with complete epiboly, characterized by embryonic axis/orientation.

Stage 13: early gastrula (Fig. 37) 

The blastoderm expands over the surface of the yolk 

and a thickened margin of the blastoderm yields a presumptive region of the embryonic shield (Fig. 39).

Stage 14: late gastrula (Fig. 38) 

The blastoderm covers approximately three-fourths 

of the yolk sphere.

Segmentation period: somites develop, organogenesis 

begins, tail appears, and early movement of embryo noted.

Stage 15: embryonic shield (Fig. 39) 

The small anlage of stage 13 increases in size; the 

embryonic shield (ES) is clearly evident at this stage.

Stage 16: head fold (Fig. 40)

The yolk sphere is nearly covered by the blastoderm. 

The head fold (HF) is a 3-dimensional structure that establishes the anterior end of the developing embryo; the 

brain, heart, and foregut develop from this anlage. Fig. 

40 illustrates stage 16 in transition to stage 17 including 

development of an optic vesicle (OpV).

Stage 17: optic vesicles (Figs. 40 and 41)

A small optic bud or rudimentary eye first appears on 

each side of the developing head.

Stage 18: somite formation begins (Figs. 41C and 42) 

Derived from the mesoderm; dermis, skeletal muscle, 

vertebra, and notochord (Noto) formation begins. Somites (So) begin to form and will increase in number 

as development continues.

Stage 19: fin fold (Fig. 43) 

The term refers to shallow membranous fins. The 

median finfold (FF) is generally the first to appear.

Stage 20: optic cup, 22-23 somites (Fig. 44) 

Somites (So) continue to develop. Optic cups (OpC) 

arise from optic vesicles and are composed of two layers 

of cells.

Stage 21: auditory placodes (Fig. 45) 

Small otic vesicles or auditory placodes (AP) appear 

but they are void of otoliths.

Stage 22: formation of lens (Fig. 46) 

A lens (L) appears in the optic cup.

Stage 23: appearance of otoliths (Fig. 47) 

Otoliths (Ot) first appear in the auditory placodes.

Pharyngula period: marked by pigmentation of the 

eye, circulation, fin development.

Stage 24: pectoral fin, 26–27 somites (Fig. 48) 

Body musculature continues to develop; a pectoral 

fin (PF) is evident.

Stage 25: pigmentation of retina (Fig. 49) 

The primitive eye now possesses several layers of cells 
37

within the retina during which the pigment layer (PL) 

of the retina first appears.

Stage 26: heart pumping (Fig. 50) 

The heart (He) begins to pulsate, suggesting that it 

possesses well defined chambers. Blood carrying channels are sophisticated, but not mature.

Stage 27: lens becomes transparent (Fig. 51) 

Originally cloudy or opaque, the lens (L) of each eye 

is now transparent.

Stage 28: openings of mouth and anus (Fig. 52) 

A thin epithelium originally covered the mouth and 

anus, but by this time, the mouth opening (M) and the 

anus are now open, indicating that the gastro-intestinal 

tract is either complete or near completion.

Stage 29: peritoneal wall pigmentation (Fig. 53) 

The peritoneum, which lines the body cavity, begins to acquire pigment granules (PG) or pigment 

cells (melanophores). Anterior pharyngeal arches 

(PA) forming lower jaw containing Meckel’s cartilage 

(Mec) are evident. By this time, the liver and other 

body cavity organs may be discernible within the body 

cavity.

Stage 30: depletion of yolk (Fig. 54) 

Prior to hatching, depletion of the pink staining 

eosinophilic yolk (Y) occurs and is greatly reduced in 

size. 

Hatching period: yolk depleted, hatching occurs just 

prior to or at the time of parturition.

Stage 31: prehatching (Fig. 55) 

Pelvic fin (PF) is easily visible and the chorion membrane (CM) envelops the entire embryo.

Stage 32: hatching (Fig. 56) 

Release of embryos from female.

Stage 33: newborn larva (Fig. 57) 
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Table 4

Comparison of rockfish development as noted by Yamada and Kusakari (1991) and Chaillé (2006). Periods of early 

development adopted from Kimmel et al. (1995). Yamada and Kusakari (1991) provide the basic developmental sequence. 

Brief embryonic development was described by Chaillé (2006) where he noted particular embryonic developmental 

differences with Yamada and Kusakari (1991). Yamada and Kusakari data presented with permission.

Developmental periods Developmental stages

(Kimmel et al., 1995) (Yamada and Kusakari, 1991) (Chaillé, 2006)

1 Mature unfertilized ovum

Zygote period

2 Formation of the germ disc (blastodisc)

Cleavage period

3 2-celled (embryo)

4 4-celled (embryo)

5 8-celled (embryo)

6 16-celled (embryo)

7 32-celled (embryo)

8 64-celled (embryo)

Blastula period

9 Morula

10 Early blastula

11 Late blastula

12 Beginning of epiboly

Gastrula period

13 Early gastrula

14 Late gastrula

Segmentation period

15 Embryonic shield

16 Head fold

17 Optic vessicles

18 Beginning of somite formation optic vesicles, 10 somites

19 Finfold

20 Optic cups, 22–23 somites

21 Auditory placodes

22 Formation of lens, motility lens, auditory placodes

23 Appearance of otoliths

Pharyngula period

24 Pectoral fins, 26–27 somites otoliths, 25–27 somites

25 Pigmentation of retina

26 Blood circulation (heart pumping)

27 Lens becomes transparent transparent lens, blood circulation

28 Openings of the mouth and anus

29 Pigmentation of the peritoneal wall 

30 Depletion of yolk, 5.4 mm body length fully formed urinary tract, reduction of yolk begins

Hatching period

31 Prehatching full somites, teeth visible; pre-hatching peristalsis

32 Hatching

33 Newborn larva, 6.2 mm body length
39

Figure 25

Mature ovum (embryonic development stage 1). Sebastes alutus collected 19 March 2004, 36 cm, 680 g. (A) 25×, (B) 160×, 

and (C) 100×.
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Figure 26

Formation of blastodisc (embryonic development stage 2). Sebastes alutus collected 19 March 2004, 32 cm, 460 g. (A) 25×, 

(B) 200×, and (C) 100×.
41

Figure 27

2-celled embryo (embryonic development stage 3). Sebastes alutus collected 18 March 2004, 40 cm, 940 g. (A) 25×, 

(B) 200×, and (C) 100×.
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Figure 28

4-celled embryo (embryonic development stage 4). Sebastes alutus collected 25 March 2004, 38 cm, 840 g. (A) 25×, (B) 200×, 

and (C) 100×.
43

Figure 29

8-celled embryo (embryonic development stage 5). Sebastes alutus collected 27 March 2004, 38 cm, 700 g. (A) 25×, (B) 200×, 

and (C) 100×.
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Figure 30

16-celled embryo (embryonic development stage 6). Sebastes alutus collected 17 March 2004, 37 cm, 660 g. (A) 25×, 

(B) 200×, and (C) 100×.
45

Figure 31

32-celled embryo (embryonic development stage 7). Sebastes alutus collected 25 March 2004, 33 cm, 520 g. (A) 25×, 

(B) 160×, and (C) 100×.
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Figure 32

64-celled embryo (embryonic development stage 8). Sebastes alutus collected 19 March 2004, 33 cm, 540 g. (A) 25×, 

(B) 160×, and (C) 100×.
47

Figure 33

Morula (embryonic development stage 9). Sebastes alutus collected 22 March 2004, 34 cm, 520 g. (A) 25×, (B) 160×, and 

(C) 100×.
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Figure 34

Early blastula (embryonic development stage 10). Sebastes alutus collected 22 March 2004, 34 cm, 620 g. (A) 25×, (B) 100×, 

inset illustrates mitotic figures, and (C) 100×.
49

Figure 35

Late blastula (embryonic development stage 11). Sebastes alutus collected 25 January 2004, 39 cm, 740 g. (A) 25×, (B) 100×, 

and (C) 100×.
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Figure 36

Beginning of epiboly (embryonic development stage 12). Sebastes alutus collected 26 January 2004, 36 cm, 580 g. (A) 25×, 

(B) 100×, and (C) 100×.
51

Figure 37

Early gastrula (embryonic development stage 13). Sebastes alutus collected 26 January 2004, 38 cm, 640 g. (A) 25×, (B) 100×, 

and (C) 100×.
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Figure 38

Late gastrula (embryonic development stage 14). Sebastes alutus collected 26 January 2004, 30 cm, 330 g. (A) 25×, (B) 100×, 

and (C) 100×.
53

Figure 39

Embryonic shield (embryonic development stage 15). Sebastes alutus collected 23 January 2004, 34 cm, 520 g. (A) 25×, 

(B) 200×, and (C) 100×.
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Figure 40

Head fold and developing optic vesicle (embryonic development stage 16 in transition to stage 17). Sebastes alutus collected 

26 January 2004, 30 cm, 340 g. (A) 25×; (B) 200×; and (C) 100×.
55

Figure 41

Optic vesicles and somite formation (embryonic development stage 17 in transition to stage 18). Sebastes alutus collected 

26 January 2004, 32 cm, 380 g. (A) 25×, (B) 200×, and (C) 100×.
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Figure 42

Somite formation begins (embryonic development stage 18). Sebastes alutus collected 26 January 2004, 36 cm, 560 g. 

(A) 25×, (B) 100×, and (C) 100×.
57

Figure 43

Fin fold (embryonic development stage 19). Sebastes alutus collected 26 January 2004, 37 cm, 600 g. (A) 25×, (B) 200×, and 

(C) 100×.
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Figure 44

Optic cups, 22-23 somites (embryonic development stage 20). Sebastes alutus collected 26 January 2004, 35 cm, 540 g. 

(A) 25×, (B) 160×, and (C) 100×.
59

Figure 45

Auditory placodes (embryonic development stage 21). Sebastes alutus collected 26 January 2004, 36 cm, 560 g. (A) 25×, 

(B) 100×, and (C) 100×.
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Figure 46

Formation of lens (embryonic development stage 22). Sebastes alutus collected 26 January 2004, 37 cm, 600 g. (A) 25×, 

(B) 100×, and (C) 100×.
61

Figure 47

Appearance of otoliths (embryonic development stage 23). Sebastes alutus collected 16 March 2004, 39 cm, 880 g. (A) 25×, 

(B) 100×, and (C) 100×.
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Figure 48

Pectoral fin, 26-27 somites (embryonic development stage 24). Sebastes alutus collected 19 March 2004, 41 cm, 1040 g. 

(A) 25×, (B) 160×, and (C) 100×.
63

Figure 49

Pigmentation of retina (embryonic development stage 25). Sebastes alutus collected 25 March 2004, 38 cm, 840 g. (A) 25×, 

(B) 200×, and (C) 100×.
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Figure 50

Heart pumping (embryonic development stage 26). Sebastes alutus collected 18 March 2004, 35 cm, 600 g. (A) 25×, 

(B) 100×, and (C) 100×.
65

Figure 51

Lens becomes transparent (embryonic development stage 27). Sebastes alutus collected 25 March 2004, 38 cm, 700 g. 

(A) 25×, (B) 100×, and (C) 100×.
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Figure 52

Openings of mouth and anus (embryonic development stage 28). Sebastes alutus collected 17 March 2004, 38 cm, 620 g. 

(A) 25×, (B) 50×, and (C) 100×.
67

Figure 53

Peritoneal wall pigmentation (embryonic development stage 29). Sebastes alutus collected 22 March 2004, 39 cm, 700 g. 

(A) 25×, (B) 160×, and (C) 100×.
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Figure 54

Depletion of yolk (embryonic development stage 30). Sebastes alutus collected 17 March 2004, 43 cm, 1000 g. (A) 25×, 

(B) 200×, and (C) 100×.
69

Figure 55

Prehatching (embryonic development stage 31). Sebastes alutus collected 17 March 2004, 42 cm, 930 g. (A) 25×, (B) 160×, 

and (C) 100×.
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Figure 56

Hatching (embryonic development stage 32). Sebastes alutus collected 2 April 2004, 42 cm, 860 g. (A) 25×, (B) 100×, and 

(C) 100×.
71

Figure 57

Newborn larva (embryonic development stage 33). Sebastes alutus collected 17 March 2004, 47cm, 1380g. (A) 25×, (B) 100×, 

and (C) 100×.
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Follicular atresia

Oocytes or embryos of Sebastes at any stage of their 

development can undergo a process of resorption, 

which is known as follicular atresia (Saidapur, 1978; 

Guraya, 1979; Agarwal, 1996). Atresia is always present 

in postovulatory follicles, but is also observed in previtellogenic and vitellogenic follicles. Resorption of 

embryos may also occur at any stage of development. 

Atresia may also occur in preovulatory follicles; atresia 

serves to limit the number of oocytes that progress to 

the next developmental stage to a number that can be 

supported by the fish (Agarwal, 1996). Various other 

physical, environmental, and health stressors will also 

affect the rate of atresia (Hunter and Macewicz, 1985; 

Schwartz et al., 2006). Bretschneider and Duyvene de 

Wit (1947), working with Rhodeus amarus, have defined 

the characteristics for four stages of atretic follicles, 

which have been used by other researchers for other 

species (Lambert, 1970; Hunter and Macewicz, 1985; 

McDermott, 1994). Atresia in the genus Sebastes takes 

place in a similar fashion, so their original description 

is closely followed here.

Stage α (Figs. 58–59)

Changes in oocyte shape and size, along with increasing size of the granulosa (GR) cells, indicate the onset of 

atresia. Atresia commences with the contraction of the 

cytoplasm and continues until the entire cytoplasm and 

nucleus are resorbed. The vitelline membrane dissolves 

and the enlarging granulosa cells begin penetrating into 

the oocyte, phagocitizing the yolk and nucleoplasm. In 

unyolked oocytes and embryos, the process is similar – 

only the elements to be phagocitized differ. All processes 

of alpha stage resorption result in an empty follicle. The 

alpha stage could be further subdivided by whether its 

origin was yolked or unyolked oocytes, or an embryo.

Stage b (Fig. 59) 

All the cytoplasm and yolk have been resorbed and 

the entire cavity is filled by granulosa cells that are increasing in size and number. The resulting structure is 

much smaller and more compact than the alpha stage, 

with noticeable disorganization in the granulosa cell layer. Large intercellular cavities are occasionally observed. 

At this stage, it is not possible to determine whether an 

oocyte started as yolked or unyolked.

Stage γ (Fig 59) 

The gamma stage follicle is much smaller than the 

previous stages, possessing a bright red hue (H&E) resulting from the possible disintegration of the granulosa 

cells. Follicle cells in the gamma stage in Sebastes are rare 

compared to the other stages.

Stage δ (Fig. 59)

The size of the atretic follicles continues to shrink in 

the delta stage until all that remains are small groups of 

granulosa cells with a characteristic dark orange-brown 

pigment (H&E).
73

Figure 58

Alpha atresia (stage α) of oocytes and embryos of Sebastes proriger (inset shows cells phagocytizing the loose 

muscle of somites indicated by arrows). Collected 15 July 1995. (A) yolked oocytes (100×), (B) unyolked 

oocyte (100×), and (C) embryo (160×).
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Figure 59

(A) Alpha atresia (stage α), (B) Beta atresia (stage β), (C) Gamma atresia (stage γ), and (D) Delta atresia 

(stage δ) yolked oocytes of Sebastes proriger (100×). Collected 15 July 1995.
75

Summary

Rockfishes of the genus Sebastes are known for being live 

bearers and long lived. Male spawning condition anticipates female maturity and during copulation, males 

transfer sperm to females via an intromittent organ. 

Females must then “preserve” transferred sperm (less 

the flagellum) until oocytes mature and are fertilized 

within the female. Females in turn produce large broods 

that may be released as a single spawn or in multiple 

spawns (Moser 1967a; MacGregor, 1970; Love, 1990; 

Takano et al. 1991). However, the number or frequency 

of annual broods may be species and age specific, as well 

as environmentally influenced (Love et al., 1990).

Whether that environmental influence is food availability or temperature remains to be determined. Moser 

(1967a), MacGregor (1970), and Love et al. (1990) 

confirmed in separate studies that many of the same 

examined species, including S. elongatus, in southern 

California were multiple brooders. However, Echeverria 

(1987) determined that in central California, only one 

of the previously examined species (S. paucispinis) was 

a multiple spawner and brooder. Still further north, 

Leaman (as cited in Love et al. 1990) did not find 

multiple brooders in any rockfish species from British 

Columbia. Our observations further indicate that S. 

elongatus is a single brooder in our area of study as we 

did not observe any secondary ova undergoing vitellogenesis during embryo development and maturation 

(Takano et al., 1991).

Gross development phases for both the testes and 

ovary are described. They are fewer in number (5) than 

histological phases and are therefore, less precise in 

reflecting gonad status. Accuracy of this method of classification, especially ovarian development, has historically been a problem (Westrheim, 1975; Chilton, 2007). 

Immature phases are often difficult to differentiate 

from late spent or resting phases and misclassifications 

sometimes occurred. To stage female maturity without 

histological confirmation, gross observations should be 

made during the time of parturition (late spring) since 

no misclassifications were made of fish sampled at these 

times (Westrheim, 1975; Chilton, 2007).

This study suggests that male and female reproductive biology of rockfish species are similar regardless 

Figure 60

Modification of the reproductive phases of fishes to 

accommodate species with alternate reproductive 

strategies. The new transition phase applies to sequential 

hermaphrodites, and the new gestation phase applies 

to livebearers. Livebearers that produce more than one 

batch of embryos during the reproductive season cycle 

between the spawning capable phase as oocytes grow 

and the gestation phase as embryogenesis proceeds 

(dashed arrow). With permission from from BrownPeterson et al. (2011).

of the number of broods produced annually. The presented phases are similar to previous rockfish gonad 

classifications with the exception of the addition of a 

regenerative phase. It is clear that although an organ 

may be spent, regenerative processes must occur for 

a subsequent spawning event, and thus the testes and 

ovaries are not resting. As a result, our current classification scheme generally agrees with that presented by 

Brown-Peterson et al. (2011) who recently called for 

standardization of terminology for describing reproductive development in fishes. In particular, our study 

appears to complement the Brown-Peterson reproductive scheme for alternative reproductive strategies 

(Fig. 60).
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