Journal of National Fisheries University 71（4）141-151（2022）

Full Paper

Growth of immature Japanese lates, Lates japonicus in the
Tomouchi River of the Gokase estuary, Kyushu Island,
Japan, by the mark and recapture method
Naohiko Takeshita1†, Takuya Kondou2, Shingo Nagata2,3 andHiroshi Takahashi1
Abstract : Growth of immature Lates japonicus in eelgrass (Zostera japonica) beds of the Tomouchi River located ataround 4.3 km upstream from the river mouth of the Gokase River, Kyushu Island, Japan was studied by the markand recapture method and scale reading from September 1998 to March 2004. Newly occurring 0-year-old L.
japonicus specimens of 13.9–78.0 mm SL (standard length) in Z. japonica beds of the Tomouchi River in August or
September reached sizes ranging 58.8–125.7 mm SL by April and 203.4–232.8 mm SL between October andNovember of the following year. Monthly changes in specific growth rates of individuals demonstrated that rapid
growth months of immature fish were limited to the period of high water temperature (22–28°C) from June to
October. Also, it was supposed that the large-sized fish of the 0-year-old fish migrated away from Z. japonica beds
after December, however a few fish remained in Z. japonica beds until the following November.
Key words : Growth; Japanese lates; Lates japonicus; Immature fish; Gokase estuary,

Introduction

effect of water temperature and salinity on feeding andgrowth14). However, there are no studies on the seasonal

Within the family Latidae fishes, one species of theand individual growth of immature L. japonicus in natural

genus Hypopterus, 11 species of the genus Lates and one

waters. For accumulation of basic ecological data and for1)

species of the genus Psammoperca have been reported .

the future conservation of L. japonicus, seasonal growth of

Except for Lates japonicus, these species distribute in theimmature fish was examined by the mark and recapture

waters between about lat. 30° N and about lat. 30° S inmethod.

the tropical and subtropical climate, although L. japonicus
occur only along the Pacific coast of southern Japan, in
the temperate climate

1, 2). L. japonicus is endemic to the

Pacific coast of southern Japan 3, 4) , and is found inestuaries and coastal waters of Miyazaki and Kochi
3)

Prefectures . It has been designated as an“endangered
6)

Materials and Methods
Study area and methods
Fieldwork was conducted in the Tomouchi River, atributary of the Gokase River, Miyazaki Prefecture,

species”by the Ministry of the Environment . This

southeastern Kyushu Island, Japan. The study area was

species has extremely low genetic diversity at the species

located at around 4.3 km upstream from the river mouth

level indicating the threatened status of it7). There haveof the Gokase River (Fig. 1). Eelgrass, Zostera japonica

been many ecological studies on this fish, including

grows in an 80 m upstream stretch and a 60 m

distribution

3, 8–10)11), occurrence of larvae and juveniles ,2)general life history , histological observation of mature
12)

13)

7)

female , feeding events , population structure , anddownstream stretch from the Tomouchi Bridge (32°36'33"N, 131°
41'42"E), varying with a width of 18–26 m.
The collections were conducted at low tide in the flood

Received date: 30 November 2022, Accepted date: 2 February 2023
Department of Applied Aquabiology, National Fisheries University, Shimonoseki, Yamaguchi, 759-6595, Japan.
2West Japan Engineering Consultants, Co., Ltd., 1-1-1 Watanabe-dori, Fukuoka, 810-0004, Japan.
3
Current address: 1438 Kyokushi-sinmei, Kikuchi, 869-1207, Japan†
Corresponding author: takeshin@fish-u.ac.jp1

142

Naohiko Takeshita, Takuya Kondou, Shingo Nagata and Hiroshi Takahashi

tide, once a month from September 1998 to April 2003

Standard length (SL) and total length (TL) were

and twice a month from May 2003 to March 2004. A

measured to the nearest 0.1 mm. Marking involved thecoarse meshed beach seine (4 mm × 4 mm square mesh,removal of the first dorsal spines and the second dorsal

26 m wide and 2 m deep with a 3 m long purse-bag at its

spine or soft rays in different combinations for specimens

center)15)

was used for collecting immature L. japonicus.

larger than ca. 40 mm SL except for in October,

The seine was spread on Z. japonica beds, crossing theNovember and December 2002 (Table 1). In theseriver and pulled by two persons so that the mouth wasmonths, no marked 88, 110, 62 individuals larger than ca.

around 3 m wide and towed over a length of 13 m long.

40 mm SL were caught, and 71 (81%), 71 (65%) and 23

Therefore, the area of 1 haul of a seine operation was(37%) individuals were randomly marked, respectively.

2

approximately 40 m . Each collection consisted of 16 to

From September 1998 to November 1999, a few ctenoid

32 hauls. Monthly changes in the number of individuals

scales from the left side of the body in the region behindof immature L. japonicus per haul of the seine operation

the pectoral fin were sampled for age determination

were estimated. After the collection, water temperaturefrom all specimens larger than ca. 40 mm SL. Also, fromand salinity of the surface and bottom layer were

December 1999 to January 2004, a few scales were

measured, below the center of Tomouchi Bridge.

similarly sampled from specimens larger than ca. 40 mm
SL, that were caught for the first time. Scales were

7@ABC

7@DBC

7@EBC
@FBG

magnification of 20.

8+/(";(</=/>-'./0/1/()'*+,@EBG

To compare growth rates for subsequent recapture,
specific growth rates (SGR) were calculated as follows:-:$5&$
8.$9:(/,+/
3"4/5+()'*+,

8.$9:(/,+/

observed using a binocular microscope with a@DBG?/%';'%(6%+/>

SGR (%) = 100 (lnL2−lnL1) T-1
where, L1 is the SL of the fish when captured, L2 is the!"#"$%&'()'*+,SL when recaptured, and T is the recapture interval(days).

G"I+"4/2",'()'*+,

Data analyses
Data were analyzed with non-parametric statistical3"4/5+()'*+,

tests (Kruskal-Wallis test and Spearman’s correlation
2:$0/H>/9/(8+/coefficient by ranks) using JMP 9 (SAS Institute Inc.).

65+()'*+,For all statistical test, significance was assessed at P =7(4#Fig. 1. Location of the study area in the Tomouchi Riverof the Gokase estuary, Kyushu Island, Japan.
467

0.05.

Table 1. Number of individuals of the total catch, marked and recaptured

Fig. 1. Takeshita et al.468
8cmimmature
Lates japonicus and their recapture rates (%) in each year class, in

470

Table 1. N umber of individuals of the total catch, marked and recaptured
Lates
japonicus
immature
and their
recapture
rates (%) in eachclass,
the Tomouchi
River,
KyushuIsland,Japan,
from September
1998 year
to Marchin the Tomouchi River, Kyushu Island, Japan, from September 1998 to
2004
March 2004

471

Year class

1998

1999

2000

2001

2002

2003

472

Total

158

30

53

110

694

703

473

Marked

81

18

35

94

201

352

474

Recaptured

44

8

16

26

129

197

475

Recapture rate (%)

54.3

44.4

45.7

27.7

64.2

56.0

469

476

Growth of immature Lates japonicus

Results

143

March.
Annual total numbers of immature L. japonicus caught

Water temperature, salinity and occurrencein the study area were 112 (39.0–123.5 mm SL) in 1998, 79

of immature fish

(14.2–211.2 mm SL) in 1999, 47 (39.9–104.1 mm SL) in 2000,

In this study area, water temperature ranged annually

94 (20.3–123.4 mm SL) in 2001, 535 (11.5–232.8 mm SL) infrom minima of 13–15°C in January to maxima of 26–28°C

2002, 855 (17.7–203.4 mm SL) in 2003 and 31 (55.1–104.9

in August (Fig. 2). Because the study area was located in

mm SL) in 2004. Monthly changes in the number of

the tidal reach, water levels varied more than over 1 m

individuals of immature L. japonicus per haul of the seine

between the low and high tide. Salinities in the bottom

operation were shown in Fig. 4. A large number of thislayer ranged from 20 to 31 ppt at low tide in spring andfish was caught usually between September andwinter (Fig. 3). However, in the wet and typhoon seasons

December although the values sharply fluctuated byafter the heavy rain, salinities of the bottom layer

year. Also, the values gradually decreased after

changed to approximately 0 ppt at low tide (Fig. 3). Z.

December. No specimens of L. japonicus were caught

japonica started to grow luxuriantly usually in May, andfrom March to September in 2000, and from January toattain a maximum height of more than ca. 80 cm fromMarch in 2001, May 2001, August 2001, August 2002 andAugust to September. After that, Z. japonica withered,February 2004.

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and their length was less than 30 cm from January to

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Fig. 2. M onthly changes in water temperature in the
Tomouchi River, Kyushu Island, Japan, from
September 1998 to March 2004 (- - - ○ - - - , surface
layer; ------●------, bottom layer).
-./0*,12314567876.+9:1;1<+.9

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Fig. 3. Monthly changes in salinity in the Tomouchi River,
Kyushu Island, Japan, from September 1998 to
March 2004 (- - - ○ - - - , surface layer; ------ ● ------bottom
layer).

%!
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Fig. 3. Takeshita et al. 8cm $
Fig. . Takeshita et al. 8cm 

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Fig. 4. Monthly changes in the number of individuals of
Lates japonicus per haul of seine in the Tomouchi
River, Kyushu Island, Japan, from September 1998
to March 2004 ( ○ , specimens were caught; ● ,specimens were not caught).

Fig. 5. Ctenoid scales of the same fish of Lates japonicus
caught in the Tomouchi River, Kyushu Island,
Japan, on 1 May (A, 78.1 mm SL) and on 12 June (B,94.4 mm SL) in 1999. Large arrow shows the clear
check, small arrow shows the unclear check. Scalebar indicates 1 mm.

144

Naohiko Takeshita, Takuya Kondou, Shingo Nagata and Hiroshi Takahashi

Annual ring formation on scale

1-year-old fish.

A scale of L. japonicus at 78.1 mm SL caught on 1 May
1999 was shown in Fig. 5A. The widely spaced ridges

General growth of immature fish

spread radially from the focal area, and the narrowly

Age of the individuals of L. japonicus was determined

spaced ridges spread radially in the outer part of theby scale reading. The specimens less than 40 mm SL, forwidely spaced ridges. The unclear check was visible onwhich scales were not sampled regarded as 0-year-old

the boundary between the wide spaced ridges and thefish. Relationships between mean values of SL for eachnarrowly spaced ridges. A scale of the same fish at 94.4

year group and the collection dates were shown in Fig. 7.

mm SL caught on 12 June 1999 was shown in Fig. 5B.

The first months when the small-sized fish were caught

The widely spaced ridges recommence to spread radiallyin the study area, were September 1998 (39.0–78.0 mm

from the outer part of the narrowly spaced ridges. The

SL), September 1999 (20.1 mm SL), October 2000 (39.9–

check was clearly visible on the boundary between the87.7 mm SL), September 2001 (27.9–77.3 mm SL),narrowly spaced ridges and the wide spaced ridges (Fig.

September 2002 (13.9–68.6 mm SL), August 2003 (17.7–

5B). Numbers of this check considered as the ring mark58.1 mm SL), respectively. They reached 62.6–106.1 mm

were read for each scale of all the specimens fromSL in December 1998, 48.6–76.6 mm SL in December

September 1998 to November 1999, and the relationships

1999, 54.6–92.0 mm SL in December 2000, 27.7–109.9 mm

between month of collection and SL were shown in Fig.

SL in December 2001, 25.5–122.7 mm SL in December

6. No fish had the clear check on the scale caught from2002, 55.4–112.6 mm SL in December 2003, respectively.

September 1998 to April 1999. One clear check was

The mean SL values of the 0-year-old fish reduced

formed in 11 % (n = 2) of specimens in May 1999, 100% (ngradually from December to March, except for the= 10) of specimens from June to August 1999. The scales

2000-year-class. By spring of the next year, they reachedof the large-sized fish 203–211 mm SL had one check

71.9–89.1 mm SL in April 1999, 77.5–84.2 mm SL in April

although the scales of the small-sized fish 35.6–71.5 mm

2001, 70.7–121.1 mm SL in April 2002, 58.8–125.7 mm SL

SL had no checks from September to November 1999.

in April 2003, respectively. Furthermore, they grew to

These results indicated that the checks on the scales

148.6 mm SL in July 2002, 170.2–203.4 mm SL inwere formed once a year between May and June. The

September 1999 and 2003, 203.4–232.8 mm SL in Octoberchecks can therefore be defined as annual rings for the2002 and 2003, 203.6–211.2 mm SL in November 1999.

-.+/0+,012*/3.415667

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Fig. 6. M onthly changes in standard length of Lates
japonicus caught in the Tomouchi River, Kyushu
Island, Japan, from September, 1998 to November,1999 ( ○ , no ring marks; ● , 1 ring mark; ,unobserved).
Fig. . Takeshita et al. 8cm 

Fig. 7. R elationship between collection date and mean
standard length of Lates japonicus in each year classcaught in the Tomouchi River, Kyushu Island,
Japan, from September 1998 to March 2004 ( ○ ,1998-year-class; ● , 1999-year-class; □ , 2000-yearclass; ■ , 2001-year-class; △ , 2002-year-class; ▲ ,2003-year-class). Vertical lines indicate standard
deviations.

Fig. . Takeshita et al. 8cm 

Growth of immature Lates japonicus#!

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Fig. 8. Standard length frequency distribution of Lates japonicus caught in the Tomouchi River, Kyushu Island,
Japan, from September 2002 to October 2003 (■, 2001-year-class; , 2002-year-class;□, 2003-year-class).

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Fig. 10. Specific growth rates (SGR) of the 2002-year-class
Lates japonicus estimated from the subsequent
recapture data of specimens in the Tomouchi
River, Kyushu Island, Japan, from September 2002
toetAugust
2003.
Fig. 0. Takeshitaal. 8cm

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Fig. 9. I ndividual growth of the 2002-year-class Lates
japonicus in the Tomouchi River, Kyushu Island,
Japan, from September 2002 to October 2003.
Identification number of the fish was indicated theremoval of the first dorsal spines and the second
dorsal spine or soft rays in different combinations,and shown as follows:----- - - ●- - -----, IV-5; ---- ○- - - - , IV・
・
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・
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Fig. . Takeshita et al. I,2;
8cm
, IV-5,7; ----- ◇ -----, IV-I,5; -------▲ -------, VII,9; - - - △- - - , VII-4,6.

146

Naohiko Takeshita, Takuya Kondou, Shingo Nagata and Hiroshi Takahashi

Occurrence and growth of 2002-year-class fish

specimens which were subsequently recaptured was

The percentage of recaptured L. japonicus of theshown in Fig. 10. SGR among the 14 time intervals were

2002-year-class was maximum, total number of that year

significantly different (Kruskal-Wallis test, χ2 = 164.2, P

class had the second largest value (Table 1), and< 0.001). SGR had high values from September tospecimens were caught consecutively from September

October 2002 and from July to August 2003, and were2002 to August 2003 (Fig. 4). Details of the occurrence

approximately 0 from December 2002 to March 2003.

and growth of this fish were described using the data ofFurthermore, relationships between the median values ofthe 2002-year-class. SL frequency distribution of L.

water temperature of the bottom layer and SGR for thejaponicus caught in the study area from September 2002

subsequent recapture, indicated that SGR had higher

to October 2003 was shown in Fig. 8. On 6 September

values in the higher water temperature periods

2002 fish of 13.9–68.6 mm SL occurred in the study area

(Spearman’s correlation coefficient by ranks, rs = 11.21, P

and on 5 October there were two peaks of individuals in< 0.001; Fig. 11).

10–20 mm SL and 60–70 mm SL, and on 4 November
2002 in 20–40 mm SL and 70–80 mm SL. After January
2003, the number of fish caught in the study area

Discussion

decreased gradually and they reached 85.6–136.8 mm SL

Growth of immature L. japonicus, in Z. japonica beds inon 11 August 2003. They reached to 139.0 mm SL on 26

the Tomouchi River located at around 4.3 km upstream

August, 170.2 mm SL on 10 September, 203.4 mm SL on

from the river mouth of the Gokase River, Kyushu

9 October 2003. The 2003-year-class fish of 17.7–46.5 mm

Island, Japan was clarified by the mark and recapture

SL first occurred in samples on 11 August 2003.

method. The first months when the small-sized fish of

Individual growth patterns of six specimens that werethe 0-year-old fish were caught in the study area, wererecaptured 5–8 times were shown in Fig. 9. They grew

September in 1998 (39.0–78.0 mm SL), September in 1999

rapidly from September to October 2002 and from June

(20.1 mm SL), October in 2000 (39.9–87.7 mm SL),to October 2003, and showed minimal growth between

September in 2001 (27.9–77.3 mm SL), September in 2002

December 2002 and April 2003.

(13.9–68.6 mm SL), and August in 2003 (17.7–58.1 mm SL),To elucidate the individual growth patterns, SGR for

respectively (Figs. 4, 6, 7). It seemed that the amount of
occurrence of immature L. japonicus in Z. japonica beds inGokase estuary fluctuated yearly (Fig. 4). Two peaks of'#"the number of individuals in 10–20 mm SL and 60–70
mm SL on 5 October 2002, 20–40 mm SL and 70–80 mm+,-./01&#"

SL on 4 November 2002 in the SL frequency distribution(Fig. 8), indicate that the migration into Z. japonica beds
occurred
several times. In the Shimanto estuary, the
!"#!$

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larvae (4.3–7.6 mm SL) and juveniles (8.1–28.0 mm SL)
occurred in Z. japonica beds located at around ca. 2–4 km"#"

upstream from the river mouth of the Shimanto River,from late July to middle August between 1985 and

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Fig. 11. R elationship between median values of watertemperature and specific growth rates (SGR) of
the 2002-year-class Lates japonicus for subsequent
recapture in the Tomouchi River, Kyushu Island,
Japan, from September 2002 to August 2003.

Fig. . Takeshita et al. 8cm 

198711). Also, the larvae (ca. 5 mm TL) were found to
migrate several times into Z. japonica beds of the
Shimanto estuary from middle July to late September
between 1998 and 1999 2). In these studies, the seine
having a mesh width of 1 mm was used16), while theGrowth of immature Lates japonicus

147

seine having a mesh width of 4 mm was used in thistemperature ranged from 28 to 32°C, and slowed down

study. Therefore, the differences in the first occurrence

markedly from May onwards17). Therefore, it seems thatmonth and size between the Gokase estuary and thethe rapid growth of L. japonicus only in the high water

Shimanto estuary are considered to be due to thetemperature season was similar to that of L. calcarifer.
The values of the number of individuals per haul ofdifferences in the mesh size of the seines.
Newly occurred 0-year-old L. japonicus in Z. japonica

seine gradually decreased after December in the Gokase

beds of the Gokase estuary in August or September

estuary (Fig. 4). Besides, the mean SL values of thereached 58.8–125.7 mm SL by the following April, and0-year-old fish reduced gradually from December to203.4–232.8 mm SL between October and November. The

March, except for the 2000-year-class (Fig. 7). It was

postlarvae (3.8–4.1 mm SL) were collected from the surf

supposed that the large-sized fish of the 0-year-old fishzone of Tei beach facing Tosa Bay, Kochi Prefecture on

migrated away from Z. japonica beds in the study area

July 10, 198211). In the Shimanto estuary, all larval andafter December. Also, it seems that a few wintering fishjuvenile L. japonicus were collected at sites with Z.

remained in Z. japonica beds in the Gokase estuary until

japonica beds, they exceeded 50 mm SL in October andNovember of the following year (Figs. 6–8). In the11)

100 mm SL by the next April at least in the estuary .

Shimanto estuary, whereas all larval and juvenile L.

Also, young L. japonicus grow to about 12 cm TL until

japonicus were collected at the sites with Z. japonica beds,

the onset of the next rainy season in the Shimanto

they exceeded 50 mm SL in October and 100 mm SL by2)

estuary . Therefore, the general growth pattern of thisthe next April at least in the estuary11). This suggests

fish in the Gokase estuary and that in the Shimanto

that they seldom move out of these waters during theestuary were similar. Furthermore, monthly changes inlarval and young period 11). Therefore, L. japonicus is

SGR by the mark and recapture method demonstrated

concluded among“residents”18) of the waters with Z.

that the months of rapid growth of immature L. japonicus

japonica beds in the estuary, utilizing this habitat at least

were limited to the period of high water temperature

for the period of postlarva to young11). Similarly, most

(22–28°C) from June to October in our study. These

young L. japonicus stay in Z. japonica beds until the onset

results were supported by the rearing examination forof the next rainy season when they have grown to about

the effect of water temperature and salinity on feeding

12 cm TL in the Shimanto estuary 2) . It seems thatand growth of this fish, the suitable water temperature

immature L. japonicus in the Gokase estuary had arange was 22 to 28°C, and the optimal water temperatureslightly longer period of remaining in Z. japonica beds

14)

range was 26 to 28°C for feeding and growth . In

than that in the Shimanto estuary.

addition, we reported that immature L. japonicus wereThis fish which may have hatched in the sea began toeuryhaline and at salinities ranging from 9 to 34 ppt

occur in the estuary from late July, i.e., after the passing

showed similar feeding and growth rates, based on theof the wet season 11). On the other hand, it has been

daily feeding rates, SGR of body weight and also on thesuggested that L. japonicus spawn in river estuaries and/14)

feeding efficiencies . Age and growth of the related

or in shallow coastal waters near river mouths based on

species barramundi, L. calcarifer has been investigated, inthe histological observation of one mature female caught

five river systems in northern Australia using scales

in the Oyodo River estuary, Miyazaki Prefecture, Japan12).

taken at the time of tagging and upon recapture17). A

However, there are no records of collections of fertilizedseasonal pattern of growth was apparent from theeggs and of newly hatched larvae of L. japonicus in Japan.

marginal increment data and from the seasonal growth

Therefore, the life history of L. japonicus remains unclear.

17)

data of the age 0+ fish . It seemed that the growth of

Early life history of the related species barramundi, L.

the 0-year-old fish appeared to be most rapid during thecalcarifer has been studied in rivers and coastal waters of

wet months (January to March), when the water

Papua New Guinea19–21) and north-eastern Queensland22).

148

Naohiko Takeshita, Takuya Kondou, Shingo Nagata and Hiroshi Takahashi

It seems that L. calcarifer has a catadromous life stylesea-grass beds and along beaches. Large number ofand spawns in the coastal waters of western Papua New

juveniles were only located in semipermanent coastal

Guinea from November to January based on theswamps, tidal creeks and the freshwater reaches of19, 21). The larvae ofrivers22). The swamp habitats and tidal creeks containing

L. calcarifer left coastal waters when less than 5 mm TL,

L. calcarifer exhibited a wide range of surface salinities,

migrating through the mangrove zone to coastal swamps

with the former ranging from freshwater to 44 ppt andwhere they remained until they were approximately 200

latter from freshwater to 38 ppt. Surface watercollection of mature females and eggs

19)mm TL . Also, the abundance of the 1-year-old class intemperatures of both habitats varied from 23 to 36°C22).

the Papua New Guinean Daru coastal region was

Destruction of nursery swamps may pose a serious

maximal in March–April, and then gradually decreased

threat to local L. calcarifer stocks near centers of humanthroughout the rest of the year20). The 2-year-old class

populations along the eastern Queensland coast22). It

showed a similar distribution pattern to that of theseems that Z. japonica beds form important nurseries for

1-year-old class. After leaving the nursery swamps, theL. japonicus in Japan, similar to the use of swamps for L.

0-year-old class became distributed throughout the Daru

calcarifer. Conservation of nursery Z. japonica beds incoastal region and by the end of their first year the fish

estuaries is therefore important for the conservation of L.

20)

had moved as far as the Fly River estuary . Therefore,japonicus in Japan.

it seems that juveniles left coastal nursery swamps whenabout 6 months old and by the end of their first year had
become distributed throughout the coastal and estuarine

Acknowledgment

regions, and during their second or third year they

The authors extend thanks to the successive presidents

moved into inland waters, although there is a residualof Tomishima freshwater fishermen’s cooperative

population of all age classes that remain resident inassociation, H. Kamakura, N. Yokoyama and H. Uchida for20)

coastal waters . In north-eastern Queensland, the early

their agreement to our study. Mr. K. Hoshino of Oita

life history of L. calcarifer has been studied by Russell

Marine Palace Aquarium and Dr. I. Ikeda and the22)

and Garrett . The larvae in the size range 2.8–5.2 mm

students of Department of Applied Aquabiology, National

TL were collected from the plankton in two estuaries in

Fisheries University for their assistance in collecting

north-eastern Queensland from 31 October 1979 until 13

specimens. Also, we extend thanks to Dr. Y. Suda ofFebruary 1980. After leaving the plankton, L. calcarifer

National Fisheries University for his lending seine from22)

moved into nearby brackish and freshwater swamps .

1998 to 2000. This study was financially supported by

These areas acted as nursery grounds, offering bothResearch group of the Kitagawa River in the River

protection from predators, and abundant prey in the

Ecology Research group of Japan from 2000 to 2002.

form of insect larvae, other fish and crustaceans. These
habitats exhibit a wide range of salinity (freshwater–44ppt) and surface water temperature (23–36°C)22). Juveniles

References

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Growth of immature Lates japonicus

151

個体識別法による五ヶ瀬川水系友内川における
アカメ未成魚の成長
竹下直彦・近藤卓哉・永田新悟・高橋洋

宮崎県五ヶ瀬川水系友内川の感潮域に繁茂するコアマモ群落（五ヶ瀬川河口から約4.3 km上流）において，1998年9月－
2004年3月に，個体識別法と鱗による年齢査定を併用して，アカメ未成魚の成長を調べた。このコアマモ群落では，8，9月に体長13.9－78.0 mmの0歳魚が出現し，それらは翌年の4月には58.8－125.7 mmに，10，11月には203.4－232.8 mmに達した。
個体識別した個体の瞬間成長率の変化から，アカメ未成魚が急速に成長するのは，高水温の6－10月（22－28℃）に限られることが明らかになった。また，アカメ0歳魚の多くは12月以降コアマモ群落を離れるが，そこで冬を越した少数の個体は11月まで留まると考えられた。