Nutritional condition, starvation status and growth of early juvenile Japanese sea bass (Lateolabrax japonicus) related to prey distribution and feeding in the nursery ground

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Journal of Experimental Marine Biolog

Nutritional condition, starvation status and growth of early juvenile

Japanese sea bass (Lateolabrax japonicus) related to prey

distribution and feeding in the nursery ground

Md. Shahidul Islam*, Masaru Tanaka

Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan

Received 10 January 2005; received in revised form 23 March 2005; accepted 4 April 2005

Abstract

The nutritional condition and protein growth rates of Japanese temperate bass larvae and juveniles were studied in relation to

prey distribution and feeding habits in the nursery grounds in Chikugo estuary, Ariake Sea, Japan. Samples were collected from a

wide spatial area covering the nursery grounds of the fish in March and April 2003. Food habits of the fish were analyzed by

examining the gut contents. Fish condition was evaluated by using RNA/DNA ratio and other nucleic acid-based indices and

protein growth rates. The nucleic acid contents in individually frozen larvae and juveniles were quantified by fluorometric method.

Two distinguished feeding patterns, determined by the distribution of prey copepods, were identified along the nursery ground.

The first pattern showed the dependency of the fish on the calanoid copepod Sinocalanus sinensis, which was the single dominant

prey in low saline upper river areas and the second pattern involved a multi-species dietary habit mainly dominated by Acartia

omorii, Oithona davisae and Paracalanus parvus. Values of RNA, DNA, total protein, growth rates and for all the nucleic acid-

based indices were higher in upstream areas than in the downstream areas. The proportion of the starving fish was higher in the

downstream areas than in the upstream areas. Condition of juvenile sea bass was not equal throughout the nursery grounds; fish

in the upper river were in better condition than those in the lower estuary. We speculated that utilization of S. sinensis, which

appears a suitable prey item and provide a better foraging environment in the upstream nursery ground, is one of the key factors

for early survival and growth of Japanese temperate bass larvae and juveniles in the Chikugo estuary.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Nutritional condition; RNA/DNA ratio; Starvation; Protein growth rate; Japanese temperate bass; Ariake Sea

0022-0981/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.jembe.2005.04.007

* Corresponding author. Tel.: +81 75 753 6225; fax: +81 75 753

6229.

E-mail address: [email protected] (Md.S. Islam).

1. Introduction

The condition of fish larvae may affect the prob-

ability of their survival because larvae in poor condi-

tion are not only more vulnerable to predation, disease

and unfavorable environmental conditions but also are

y and Ecology 323 (2005) 172–183

Md.S. Islam, M. Tanaka / J. Exp. Mar. Biol. Ecol. 323 (2005) 172–183 173

less efficient in foraging (Amara and Galois, 2004).

Therefore, assessment of the nutritional condition of

field-caught larvae helps to predict larval survival and

year-class fluctuations (Richard et al., 1991). RNA/

DNA ratio has been proven as a useful and reliable

indicator of nutritional condition and growth of larval

and juvenile fishes that has been widely applied to

laboratory-reared as well as wild fishes (Buckley,

1980; Clemmesen, 1987, 1988; Robinson and Ware,

1988; Bailey et al., 1995; Rooker and Holt, 1996;

Canino, 1997; Chicharo, 1997, 1998; Chicharo et

al., 1998a,b; Buckley et al., 1999). The quantity of

DNA in most animal cells is believed to be normally

stable but RNA quantity varies with physiological

status, the requirement for protein synthesis and

growth (Buckley et al., 1999). Because mRNA,

tRNA and rRNA are essential for the biosynthesis of

protein, the quantity of bulk RNA in a cell varies in

response to changes in demand for protein synthesis.

RNA quantities are high in rapidly growing organisms

(Bergeron, 1997; Buckley et al., 1999); any factor

preventing or slowing growth is reflected by a reduc-

tion in RNA quantities. Among such factors, the

nutritional condition seems to be the most studied

and the most widely used. Nutritional condition is

associated with food supply and feeding success of

the fish and, therefore, variability in the trophic envir-

onment is reflected in the nutritional condition of fish.

Since the larval stage of fish is characterized by rapid

exponential growth (i.e., rapid protein synthesis),

RNA/DNA ratio is a good index of relative growth

rate (Buckley et al., 1999), reflecting the role of

variable trophic environment in the field.

Japanese temperate bass (Lateolabrax japonicus),

one of the dominant members of the fish assemblage

of Ariake Sea, is an important species of the commer-

cial as well as sport fishery and a highly promising

species for sea farming in winter (Matsumiya et al.,

1982). This is also an ecologically important species

because, in Ariake Sea, the fish is an endemic species

and is genetically unique and an independent popula-

tion. Nursery grounds of the fish are located in the

estuarine waters and the life history is characterized

by river ascension to arrive in fresh water nursery

areas from the sea. Therefore, the species is highly

suitable for the study of larval ecophysiology because

the fish is exposed to severe environmental changes.

However, the role of different habitats in supporting

larval and juvenile Japanese sea bass and the nutri-

tional condition of the bass in the nursery grounds

have not been clarified yet. In the present study, we

have described the spatial patterns in dietary habits of

the larval and early juvenile Japanese sea bass and

have attempted to investigate the growth rates and

condition of larval and early juvenile Japanese sea

bass along the estuary using RNA/DNA ratio and

other nucleic acid-based indices.

2. Materials and methods

2.1. The study area and sampling

The Ariake Sea, the largest tidal wetland of Japan, is

located at the southwestern part of Japan. The Chikugo

estuary is the largest estuary of the Ariake Sea, with the

highest tidal differences in Japan. Seven sampling sta-

tions were set up along Chikugo estuary (Fig. 1). The

sampling stations are lined along the tideway of the

Chikugo River. Among them, four stations were posi-

tioned along the river (R4–R1) and the other three

were outside the river mouth along the estuary (E1–

E3). Station R1 is located at the river mouth and R4 is

the uppermost station, 16 km upstream from the

mouth and with little seawater influence even at spring

high tide. Starting from the river mouth, the estuarine

stations were positioned on the tidal flat and E3 is the

most distant station with the highest salinity.

Larval and juvenile fish samplings at selected sta-

tions were carried out by two research cruises in March

and April 2003. Samples were collected by surface

towing with a larval ring net (1.3 m mouth diameter, 1

mm mesh size along the body and 0.33 mm mesh size

at the cod end) for 10 min against tidal flow. Sea bass

samples were sorted and immediately frozen on dry ice

on board and transported to the laboratory for subse-

quent storage in a deep freezer at �85 8C. All larvaeand juveniles were counted, total length (TL) was

measured to the nearest 0.1 mm with a digital slide

calipers and weight was measured with a sensitive

electronic balance to the nearest 0.1 mg.

During each cruise, hydrographic data and plank-

ton samplings were also carried out. Temperature and

salinity were recorded at each station by an Environ-

mental Monitoring System (YSI 650 MDS, YSI Incor-

porated, USA). Copepod samples were collected by

R4

R3

R2

R1

E1

E2

E3

Japan Sea

Pacific Ocean

5 km

Ariake Sea

Ariake Sea

Chikugo River

Fig. 1. Map of Ariake Sea and Chikugo River estuary showing the sampling stations; the scale applies only to the spatial areas used for sampling.

Md.S. Islam, M. Tanaka / J. Exp. Mar. Biol. Ecol. 323 (2005) 172–183174

oblique towing a plankton net (45 cm mouth diameter,

0.1 mm mesh). Copepod samples were preserved in

10% seawater formalin on the board.

2.2. Sample analyses

A minimum of 10 fishes at each station were ran-

domly selected for gut study. The guts were opened and

food organisms were separated from the esophagus to

the rectum and were examined under microscope. Prey

organisms were counted and identified to the lowest

possible taxonomic level. Copepods were sorted from

the suspended particles and detritus under a binocular

stereomicroscope and the qualitative composition was

determined by identifying and counting the number.

A total of 167 bass larvae and early juveniles

ranging in length from 15.2 mm to 31.3 mm (mean

22.6F3.01 mm) and weight from 27.4 mg to 257.8

mg (mean 97.0F44.1 mg) were used for nucleic acid

analysis. Measurements of RNA, DNA and protein

contents were carried out for individually frozen fish

samples. Nucleic acids were extracted from the whole

0

3

6

9

12

15

18

0

5

10

15

20

25

30

R4 R3 R2 R1 E1 E2 E3

MarchAprilMean

Sampling stations

Sal

init

y (P

SU

) T

emp

erat

ure

(0 C

)

Fig. 2. Variation in temperature and salinity along Chikugo estuary.

Temperature was fairly stable over the spatial scale, while there was

a salinity gradient with increasing salinity downstream.

0

11

22

33

44

55

R4 R3 R2 R1 E1 E2 E3

March April

Sampling stations

Nu

mb

er o

f fi

sh

Fig. 3. The number of larval and juvenile fish collected form seven

sampling stations along Chikugo estuary during March and Apri

2003. The upstream areas had generally higher number of fish than

the lower estuary.


body by homogenizing the sample in ice-cold Tris–

EDTA buffer (0.05 M Tris, 0.1 M NaCl, 0.01 M

EDTA, pH 8.0) using a glass homogenizer and sub-

sequently transferring to a mixture of Tris–EDTA

buffer, proteinase-K (pro-K) and sodium dodecyl sul-

fate (SDS). The quantity of RNA and DNA in the

whole body was determined by the fluorescence-

photometric technique using a specific nucleic acid

fluorescent dye—ethidium bromide (Nacalai Tesque

Co. Ltd., Kyoto, Japan), as described by Clemmesen

(1993) and slightly modified by Sato et al. (1995). In

order to measure the DNA content of a sample, RNA

was enzymatically digested with RNAase and the

remaining quantity of DNA was determined with

ethidium bromide. The fluorescence due to total

RNA was calculated as the difference between total

fluorescence (RNA and DNA) and the fluorescence

after RNAase treatment, which is assumed to be due

to presence of only DNA. Salmon sperm DNA (Wako

Pure Chemical Co. Ltd.) and yeast RNA (Kanto Che-

mical Co. Ltd.) were used as standards. RNA and

DNA contents are both expressed as milligrams per

fish. Total protein (dissolved in NaOH) was deter-

mined by a Bio-Rad protein kit (Bio-Rad, Tokyo,

Japan) using bovine serum albumin as a standard.

Results are expressed as milligrams of protein per

fish; the ratio of RNA to protein and protein to

DNA content are cited as indices of protein synthesis

capacity and cell size, respectively (Buckley et al.,

1999). The instantaneous protein growth rate (Gpi)

was calculated from the larval growth model based on

the RNA:DNA values and temperature; the model,

proposed by Buckley (1984), was given as

Gpi ¼ 0:93T þ 4:75 RNA=DNAð Þ � 18:18 ð1Þ

where Gpi is the protein growth rate (% day�1) and T

is the water temperature.

2.3. Statistical analysis

One-way analysis of variance (ANOVA) was used

separately to examine the spatial (between stations)

and temporal (between cruises) variations in different

parameters studied. Effects of fish size (length and

weight) and hydrographical parameters (temperature

and salinity) on fish condition parameters were

assessed by simple linear regression analysis. Values

were considered significant at 5% level of confidence.

3. Results

3.1. Hydrography and fish distribution

Temperature ranged 10.9–11.6 8C (mean

11.3F0.23 8C) in March and 16.6–16.8 (mean

l

MarchM = 21.83 ± 2.27

N = 230

0

5

10

15

20

AprilM = 26.01 ± 2.96

N = 155

0

5

10

15

20

10 15 20 25 30 35

Fre

qu

ency

(%

)

TL (mm)

Fig. 4. Total length frequency distribution of the fish collected

during two sampling cruises in March (upper) and April (lower)

along the Chikugo estuary.

0

5

10

1520

25

30

35

40

0

50

100

150

200

250

300

R4 R3 R2 R1 E1 E2 E3

March April

Sampling stationsT

L (

mm

)W

eig

ht

(mg

)

Fig. 5. Spatial variations in the mean total length (TL) and body

weight of all larvae and juveniles collected during two sampling

cruises in March and April 2003 along the Chikugo estuary: show-

ing larger fish sizes in the upstream areas than that in the down-

stream areas.


16.7F0.08) in April, with no significant (P b0.05)

spatial variations (Fig. 2). Temperature was signifi-

cantly higher (P b0.05) in April than in March. Sali-

nity showed gradual increase from stations R4 to E3

and ranged 0.14–28.5 in March and 0.12–27.5 in

April (Fig. 2). Salinity showed significant spatial

differences but did not differ significantly between

the two cruises (P b0.05). Distribution of the fish

Table 1

Results of one-way analysis of variance (ANOVA) comparing parameters between stations and between years (s=significant, ns=no

significant)

Between stations Between months

MS F P Remark MS F P Remark

Temperature 0.0274 0.0019 1.0000 ns 101.521 2842.58 0.0000 s

Salinity 267.628 58.893 0.0000 s 19.873 0.147416 0.7077 ns

TL 39.325 4.960 0.0001 s 607.279 111.692 0.0000 s

Weight 5620.68 3.113 0.0065 s 132805.2 115.452 0.0000 s

RNA 4.127 5.603 0.0000 s 57.745 112.2553 0.0000 s

DNA 0.1247 2.2997 0.0370 s 3.608 102.325 0.0000 s

Protein 77.448 2.030 0.0646 ns 2967.40 135.970 0.0000 s

RNA/DNA 3.372 9.394 0.0000 s 9.241 22.284 0.0000 s

RNA/protein 0.0278 9.175 0.0000 s 0.0291 7.721 0.0061 s

Protein/DNA 95.795 4.712 0.0002 s 1101.73 66.687 0.0000 s

Gpi 149.3047 8.622439 0.0000 s 2146.65 233.068 0.0000 s

extended over a wide range of salinity from about 0

PSU in the upstream to as high as 29 PSU in the sea

and fish were collected in all seven stations during

both cruises; however, there was no clear spatial

pattern in fish abundance (Fig. 3). A total of 411

(256 in March and 155 in April) bass larvae and

t


juveniles were collected with the mean total length of

21.83F2.27 mm in March and 26.0F2.96 mm in

April (Fig. 4). Significant spatial and temporal varia-

tions in fish length and weight were observed (Table

1). Fish length and weight were higher in upstream

areas in the river than in the downstream areas and in

April than in March (Fig. 5, Table 1).

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

R4 R3 R2 R1

Co

pep

od

co

mp

osi

tio

n in

wat

er (

%)

Gu

t co

nte

nt

com

po

siti

on

(%

)

Sampling stati

March

March

April

April

Fig. 6. Copepod composition (upper two graphs) in water and gut conten

along the Chikugo estuary. The low saline upper estuary was characterized

the high saline lower estuary had a multi-species assemblage, dominated

3.2. Copepod assemblage in water and gut content of

fish

A total of 9 zooplankton types, mainly copepods,

were recorded; they were: Sinocalanus sinensis, Acar-

tia omorii, Paracalanus parvus, Oithona davisae,

Calanus sinicus, Pseudodiaptomus marinus, Coryac-

E1 E2 E3

OthersMysis NaupliiP. marinusC. sinicusP. parvusCopepoditeO. davisaeA. omoriiS. sinensis

ons

ts composition (%) of fish larvae and juveniles (lower two graphs)

by the dominance of a single species (Sinocalanus sinensis), while

by Acartia omorii and Oithona davisae.


eous affinis, unidentified copepodite and decapod

mysis (Fig. 6). Copepod composition (%) in water

at each station (Fig. 6) showed that S. sinensis was

overwhelmingly dominant along the low saline areas,

especially in stations R4 and R3, and was the single

dominant copepod species recorded in these two sta-

tions where this species contributed 97.7–98.8% in

March and 94.5–96.4% in April. In contrast to the low

salinity upper estuary, a multi-species assemblage was

0

5

10

15

20

25

30

0

50

100

150

200

0

1

2

3

4

0

0.2

0.4

0.6

0.8

1

1.2

1.4

R4 R3 R2 R1 E1 E2 E3

MarchAprilMean

TL

(m

m)

Wei

gh

t (m

g)

RN

A (

mg

fis

h-1

)D

NA

(m

g f

ish

-1)

Sampling stations

Fig. 7. Spatial variations in the nucleic acid-based indices in individual sea

during March and April 2003. Significant spatial variations were observed

values in the upstream areas indicating better condition.

observed in the high salinity lower estuary (stations

R1–E3), which was mainly dominated by A. omorii

(39.2–55.5%) in March and by P. marinus (36.3–

49.7%) in April (Fig. 6). The other species in these

regions include O. davisae, C. sinicus, P. parvus and

C. affinis.

Among the prey types, 8 species of copepods

were recorded that contributed as much as 97.7% of

the total diet. Profound influence of the distribution

0

5

10

15

20

25

30

0

1

2

3

4

0

0.1

0.2

0.3

0

5

10

15

20

25

R4 R3 R2 R1 E1 E2 E3

MarchAprilMean

Pro

tein

(m

g f

ish

-1)

RN

A:D

NA

RN

A:p

rote

inP

rote

in:D

NA

Sampling stations

bass larvae and early juveniles collected along the Chikugo estuary

in almost all the parameters (see Table 1 for statistics), with higher

0

4

8

12

16

20

R4 R3 R2 R1 E1 E2 E3

March

April

Sampling stations

GP

i (%

day

-1)

Fig. 8. Spatial variations in the protein growth rate (Gpi) of

individual larvae and juveniles of Japanese temperate bass collected

along the Chikugo estuary. Significantly higher growth rates were

observed in the fish collected in the upper estuary than those

collected downstream (see Table 1 for statistics).


pattern and salinity was observed on the food habit

of each species. The gut contents of the fishes at

low-to-medium salinity zones (stations R4–R2) were

highly dominated by a single species of copepod, S.

sinensis in both years (Fig. 6). In these stations, S.

sinensis contributed nearly 100% of the prey con-

sumption. In contrast to the mono-specific gut com-

position in the low saline area, a multi-species gut

assemblage, dominated by A. omorii, O. davisae and

decapod mysis, was observed in the high saline lower

estuary in both years. Minor prey items in these

regions include P. parvus, C. sinicus, P. marinus, C.

affinis and unidentified copepodite (Fig. 6).

3.3. Nutritional condition

The mean RNA, DNA, protein, RNA/DNA ratio,

RNA/protein ratio and protein/DNA ratio and corre-

sponding mean length and weight of the fish ana-

lyzed in March and April (Fig. 7) showed a high

degree of spatial variability in all the parameters, with

a general trend of higher values in upstream stations

(stations R4–R2). The total length and weight of fish

used for biochemical analyses were significantly

higher in upper river areas than in the lower estuaries

in both March and April (Fig. 7) and also differed

significantly between the two cruises (Table 1). RNA,

DNA, RNA/DNA ratio and RNA/protein ratio

showed significant variations between stations and

between cruises; values were generally higher in the

upstream areas of the river than in the sea and in April

than in March (Fig. 7). Total protein content did not

show significant spatial variation but was significantly

higher in April than in March. In contrast to the RNA-

based ratios (RNA/DNA and RNA/protein), signifi-

cantly higher values of protein/DNA ratio were

recorded in the estuarine stations than in the upstream

stations (Fig. 7). However, similar to the RNA-based

ratios, significantly higher protein growth rates were

observed in fish collected from the upstream areas

than those collected in the sea (Fig. 8, Table 1).

While the amount of RNA, DNA and protein had

significant relation with fish length and body

weight, RNA/DNA ratio, RNA/protein ratio, pro-

tein/DNA ratio and protein growth rate did not

have significant relation with either fish length or

fish body weight (Table 1, Fig. 9). Regression ana-

lysis RNA/DNA ratio with temperature and with sali-

nity showed that spatial variations in the RNA/DNA

ratios were not related to either temperature or salinity

(Table 2).

Spatial scale of starvation status was determined

on the basis of the values reported in other studies

(Martin et al., 1985 in striped bass and Robinson and

Ware, 1988 in Atlantic herring); they reported the

critical RNA:DNA value of 2.0 for starving fish for

these two species. Based on the reported critical value,

6.7–40.0% fish were identified as starved in March

and 3.0–40.0% fish were starving in April. Starvation

rates were higher in the downstream stations than in

the upstream stations, with no fish found starving in

the three uppermost stations (Fig. 10).

4. Discussion

The distribution found in the present study is

typical for the early life condition of this fish

species (Matsumiya et al., 1982, 1985; Hibino et al.,

1999). Fish were distributed over wide estuarine areas

and, therefore, showed a high degree of plasticity to

salinity and were collected from all seven stations.

The fish showed a highly degree of plasticity in their

food habit also; plasticity to environmental changes

and feeding may be important factor for a wide spatial

distribution. The results of the gut analyses shows that

S. sinensis is the most important food item in the

upstream stations (stations R4–R2) and A. omorii

and O. davisae were major species of the gut contents

0

1

2

3

4

5

RNADNA

0

1

2

3

4

5

0

5

10

15

20

25

30

35

40

0

5

10

15

20

25

30

35

10 15 20 25 30 35

Protein:DNA Gpi

0

1

2

3

4

5

RNADNA

0

1

2

3

4

5

0

5

10

15

20

25

30

35

40

0

5

10

15

20

25

30

35

0 50 100 150 200 250 300

Protein:DNA Gpi

RN

A &

DN

A (

µg f

ish

-1)

RN

A:D

NA

Pro

tein

(m

g f

ish

-1)

TL (mm) Weight (mg)

Pro

tein

:DN

A &

GP

i

Fig. 9. Relationships of the nucleic acid-based indices with total length and weight of larval and juvenile Japanese sea bass collected along the

Chikugo estuary. The regression relations were RNA=0.27TL�3.94 (R2=0.79, P=0.000), DNA=0.07TL�0.79 (R2=0.73, P=0.000),

protein=1.71TL�27.64 (R2=0.67, P=0.000), RNA/DNA=0.12TL+0.28 (R2=0.26, P=0.322), protein/DNA=0.87TL�5.24 (R2=0.30,

P=0.029), Gpi=�0.43TL+17.56 (R2=0.07, P=0.000), RNA=0.02W +0.36 (R2=0.78, P=0.000), DNA=0.01W +0.27 (R2=0.79,

P=0.000), protein=0.13W�1.23 (R2=0.77, P=0.000), RNA/DNA=0.01W +2.18 (R2=0.21, P=0.000), protein/DNA=0.06W +8.28

(R2=0.33, P=0.000) and Gpi=�0.03W +10.39 (R2=0.06, P=0.000). While RNA and DNA had significant relations with total length and

weight of fish, RNA/DNA ratio did not have significant relation with either TL or weight of fish; the protein/DNA ratio and the protein growth

rate also showed no relation with TL and weight, indicating that nutritional condition of fish was not confounded by fish size.


in the other downstream stations. The prey organisms

in the guts of the bass were representative of the prey

types in water.

Values of RNA/DNA ratios reported in the field

show considerable variability depending on the spe-

cies studied as well as the location (Rooker et al.,

Table 2

Results of the regression analysis between RNA/DNA ratio and

temperature and salinity during the two sampling cruises in Chikugo

estuary, Ariake Sea (R/D=RNA/DNA ratio, T =temperature,

S =salinity, ns=not significant)

Cruise Regression equation R2 value P df Significance

March R/D=�0.8329T +12.217 0.1388 0.411 1.5 ns

April R/D=�2 .0479T +36.975 0.1072 0.474 1.5 ns

March R/D=�0.0168S +3.2811 0.1243 0.438 1.5 ns

April R/D=�0.0231S +3.3416 0.1846 0.336 1.5 ns

0

8

16

24

32

40

R4 R3 R2 R1 E1 E2 E3

MarchAprilMean

Sta

rvat

ion

rat

e (%

)

Sampling stations

Fig. 10. Starvation rates (%) of the larval and juvenile fish collected

from seven sampling stations along Chikugo estuary, as determined

on the basis of RNA/DNA values, indicated a downstream increase

in the number of starved fish.


1997). Chicharo (1998) reported RNA/DNA values of

sardine (Sardina pilchardus) being 2.3–4.82 with 1.3

as the critical value, below which fish were considered

as starved, while Lough et al. (1996) reported 5.23–

5.96 for cod and 4.74–5.87 for haddock with a critical

value of 4.1 for both. Martin et al. (1985) reported

RNA/DNA ratios of striped bass ranging 0.9–11.9 in

Potomac River estuary, USA and determined that the

critical value for the fish is 2.0 in laboratory condi-

tions. Our results of RNA:DNA values which ranged

1.29–7.82 (2.93F0.99) are in strong agreement with

Martin et al. (1985). The critical values of RNA/DNA

ratios as well as the starvation status are also species

as well as site-specific, depending upon the physical

environmental conditions and food supply in a parti-

cular area. Although the starvation rates reported in

the present paper were calculated indirectly and are,

therefore, not exclusively reliable estimates, we report

a reliable scale for between-station comparison which

showed that a higher proportion of the fish in the

estuary is starving as compared to the river (Fig.

10), indicating a better feeding environment and

potential nursery ground in the upstream areas of

Chikugo estuary. The significant between stations

differences in each of the nucleic acid-based indices

indicate that all the nursery habitats within a cruise

were not equivalent in promoting growth, and pre-

sumably survival in Japanese sea bass larvae and

juveniles in this area. This was the central question

of this study, which covered almost the total nursery

ground of this species. Based on the nucleic acid-

based indices and the starvation status, it can be

speculated that fish in the upper regions were in better

condition than in lower estuaries.

The underlying factors that govern the spatial var-

iations in fish condition have been discussed by many

authors (Buckley, 1982; Buckley et al., 1999; Clem-

mesen, 1994; Imsland et al., 2002). The major factors

involved in changing fish condition in the field

include the hydrological parameters, fish length and

weight, and the food supply, both qualitative and

quantitative. Of the hydrological variables that play

potential role in fish condition, temperature is

believed to be the most prominent due to its direct

involvement in both foraging behavior and food uti-

lization by fish. In our study, temperature did not

show significant spatial variation and, therefore, tem-

perature is less likely to play a role in fish condition

over the narrow spatial scale studied. Salinity showed

significant spatial variations; however, regression ana-

lysis did not show significant relation between RNA/

DNA ratio and salinity, indicating that fish condition

was not related to salinity. Field studies have not

consistently indicated a correlation between fish

length and RNA/DNA ratio (Lough et al., 1996;

Chicharo et al., 1998a,b). RNA/DNA values, when

plotted against TL and weight, produced no signifi-

cant relations with either TL or weight of fish (Fig. 9),

suggesting that the variations in fish condition were

not confounded by fish size. Another important factor

that affects individual fish condition is the larval

ontogeny; as larvae progress through stages of onto-

genic development and growth, some of the stages

require more protein synthesis and therefore might

cause a lower RNA/DNA ratio even if the fish are

well fed. This factor may contribute substantially to

the observed pattern of spatial differences in fish

condition. However, the effects of ontogenic develop-

ment are particularly important in pre-metamorphic


larvae and, in the present study, we used fish that had

already metamorphosed to early juveniles, to avoid

the effects of ontogeny.

Several authors have suggested that changes in

condition of larval and juvenile fishes may be brought

about by particular prey types probably by virtue of

their nutritional quality. Martin et al. (1985), for

example, reported that the condition of striped bass

in the Potomac River estuary was highly influenced

by cladoceran Bosmina abundance; they reported that

the lowest level of starvation and better condition of

the fish was associated with highest abundance of this

prey species. Canino et al. (1991) studied the feeding

and condition of walleye pollock inside and outside of

a plankton patch in Shelikof Straight of the Gulf of

Alaska and found that the distribution and condition

of the fish was strongly associated with the concen-

tration of copepod nauplii. They reported reduced

feeding intensity and lower RNA/DNA ratio in areas

of lower nauplier concentration outside the plankton

patch than in areas of higher nauplier concentration

inside the plankton patch. We also consider that the

spatial variation in fish condition in the present study

was caused among others by food quality, particularly

by S. sinensis which was abundant in the upper

region, which is also evident from the comparison

of the gut contents of the fish between the two

regions. We suppose that the better quality of the

fish in the upper river was contributed by this copepod

species, presumably by virtue of its better nutritional

quality. Similar to our result, significant between sta-

tion differences in nutritional condition of larval

anchovy (Engraulis mordax) were reported by Hakan-

son (1989) in the Southern California Bight, where the

between station variation was associated with the

energy storage in a specific prey copepod Calanus

pacificus. Similar influence of prey quality was also

reported by Davis and Olla (1992) in walleye pollock

(Theragra chalcogramma) larvae.

The results of the present study indicate that star-

vation may be a significant source of mortality during

early life stages of the fish in the lower estuary of

Chikugo; the condition of the fish as indicated by the

RNA/DNA ratios and other nucleic acid-based indices

and growth rates infer suboptimal growth and

extended duration at size which may contribute to

predation mortality in early life stages in the lower

estuary. It could be hypothesized that the fish undergo

ascending migration as an adaptation to reduce this

early mortality by utilizing a better foraging ground in

the upper estuary which is occupied by S. sinensis,

which appears a suitable prey copepod for the juvenile

bass and provide better condition in the upper regions.

It could be speculated that utilization of S. sinensis in

the upstream nursery grounds is one of the most

important factors for early survival and growth in

Japanese temperate bass along the Chikugo estuary.

Acknowledgements

[SS]

References

Amara, R., Galois, R., 2004. Nutritional condition of metamorphos-

ing sole: spatial and temporal analyses. J. Fish Biol. 64, 72–88.

Bailey, K.M., Canino, M.F., Napp, J.M., Spring, S.M., Brown, A.L.,

1995. Contrasting years of prey levels, feeding conditions

and mortality of larval walleye pollock Theragra chalco-

gramma in the western Gulf of Alaska. Mar. Ecol. Prog. Ser.

119, 11–23.

Bergeron, J.P., 1997. Nucleic acids in ichthyoplankton ecology: a

review, with emphasis on recent advances for new perspectives.

J. Fish Biol. 51 (Suppl. A), 284–302.

Buckley, L.J., 1980. Changes in ribonucleic and deoxyribonucleic

acid, and protein content during ontogenesis in winter flounder

Pseudopleuronectes americanus, and effect of starvation. Fish.

Bull. U.S. 77, 703–708.

Buckley, L.J., 1982. Effects of temperature on growth and biochem-

ical composition of larval winter flounder (Pseudopleuronectes

americanus). Mar. Ecol. Prog. Ser. 8, 181–186.

Buckley, L.J., 1984. RNA/DNA ratio: an index of larval fish growth

in the sea. Mar. Biol. 80, 291–298.

Buckley, L.J., Caldarone, E., Ong, T.L., 1999. RNA–DNA ratio and

other nucleic acid-based indicators for growth and condition of

marine fishes. Hydrobiologia 401, 265–277.

Canino, M.F., 1997. Nucleic acid contents and growth of first-

feeding walleye pollock larvae in response to prey densities

typical of sub-artic ecosystems. J. Fish Biol. 51, 41–52.

Canino, M.F., Bailey, K.M., Incze, L.S., 1991. Temporal and geo-

graphic differences in feeding and nutritional condition of wal-

leye pollock larvae Theragra chalcogramma in Shelikof

Straight, Gulf of Alaska. Mar. Ecol. Prog. Ser. 79, 27–35.

Chicharo, M.A., 1997. Starvation percentages in field caught Sar-

dina pilchardus larvae off southern Portugal. Sci. Mar. 61 (4),

507–516.

Chicharo, M.A., 1998. Nutritional condition and starvation in Sar-

dina pilchardus (L.) larvae off southern Portugal compared

with some environmental factors. J. Exp. Mar. Biol. Ecol.

225, 123–137.


Chicharo, M.A., Chicharo, L., Valdes, L., Lopez-Jamar, E., Re, P.,

1998a. Does the nutritional condition limit survival potential of

sardine Sardina pilchardus (Walbaum, 1792) larvae off the

north coast of Spain? RNA/DNA ratios and their variability.

Fish. Res. 39, 43–54.

Chicharo, M.A., Chycharo, L.M., Valdez, L., Lopez-Jamar, E., Re,

P., 1998b. Estimation of starvation and diel variation of the

RNA/DNA ratios in field-caught Sardina pilchardus larvae off

the north of Spain. Mar. Ecol. Prog. Ser. 164, 273–283.

Clemmesen, C., 1987. Laboratory studies on RNA/DNA ratios of

starved and fed herring (Clupea harengus) and turbot

(Scophthalmus maximus) larvae. J. Cons.-Cons. Int. Explor.

Mer 43, 122–128.

Clemmesen, C., 1988. An RNA and DNA fluorescent technique to

evaluate the nutritional condition of individual marine fish

larvae. Meeresforschung 32, 134–143.

Clemmesen, C., 1993. Improvements in the fluorometric determina-

tion of the RNA and DNA content of individual marine fish

larvae. Mar. Ecol. Prog. Ser. 100, 177–183.

Clemmesen, C., 1994. The effect of food availability, age or size on

the RNA/DNA ratio of individually measured herring larvae:

laboratory calibration. Mar. Biol. 118, 377–382.

Davis, M.W., Olla, B.L., 1992. Comparison of growth, behavior and

lipid concentrations of walleye Pollock Theragra chalco-

gramma larvae fed lipid enriched, lipid deficient and field

collected prey. Mar. Ecol. Prog. Ser. 90, 23–30.

Hakanson, J.L., 1989. Condition of larval anchovy (Engraulis

mordax) in the Southern California Bight, as measured through

lipid analysis. Mar. Biol. 102, 153–159.

Hibino, M., Ueda, H., Tanaka, M., 1999. Feeding habits of Japanese

temperate bass and copepod community in the Chikugo River

estuary, Ariake Sea, Japan. Nippon Suisan Gakkaishi 65 (6),

1062–1068.

Imsland, A.K., Foss, A., Bonga, S.W., Ham, E.V., Stefansson, S.O.,

2002. Comparison of growth and RNA:DNA ratios in three

populations of juvenile turbot reared at two salinities. J. Fish

Biol. 60, 288–300.

Lough, R.G., Galdarone, E.M., Rotunno, R.K., Broughton, E.A.,

Burns, B.R., Buckley, L.J., 1996. Vertical distribution of cod

and haddock eggs and larvae, feeding and condition in stratified

and mixed waters on southern Georges Bank, May 1992. Deep-

Sea Res., Part II 43 (7–8), 1875–1904.

Martin, F.D., Wright, D.A., Means, J.C., Setzler-Hamilton, E.M.,

1985. Importance of food supply to nutritional state of larval

stripped bass in the Potomac River estuary. Trans. Am. Fish.

Soc. 114, 137–145.

Matsumiya, Y., Mitani, T., Tanaka, M., 1982. Changes in distribu-

tion pattern and condition coefficient of the juvenile Japanese

sea bass with the Chikugo River ascending. Bull. Jpn. Soc. Sci.

Fish. 48 (2), 129–138.

Matsumiya, Y., Masumoto, H., Tanaka, M., 1985. Ecology of

ascending larval and early juvenile Japanese sea bass in the

Chikugo estuary. Nippon Suisan Gakkaishi 51, 1955–1961.

Richard, P., Bergeron, J.P., Boulhic, M., Galois, R., Person-Le

Ruyet, J., 1991. Effect of starvation on RNA, DNA and protein

content of laboratory-reared larvae and juveniles of Solea solea.

Mar. Ecol. Prog. Ser. 72, 69–77.

Robinson, S.M., Ware, D., 1988. Ontogenetic development of

growth rates in larval Pacific herring, Clupeaharengus pallasi,

measured with RNA/DNA ratios in the Strait of Georgia, British

Columbia. Can. J. Fish. Aquat. Sci. 45, 1422–1429.

Rooker, J.R., Holt, G.J., 1996. Application of RNA:DNA ratios to

evaluate the condition and growth of larval and juvenile red

drum (Sciaenops ocellatus). Mar. Freshw. Res. 47, 283–290.

Rooker, J.R., Holt, G.J., Holt, S.A., 1997. Condition of larval and

juvenile red drum (Sciaenops ocellatus) from estuarine nursery

habitats. Mar. Biol. 127, 387–394.

Sato, C., Kimura, R., Nakata, K., Umeda, S., Suzuki, M., 1995.

RNA/DNA ratio of first-feeding larvae of Japanese sardine.

Fish. Sci. 61, 538–539.

Documents

Nutritional condition, starvation status and growth of early juvenile Japanese sea bass (Lateolabrax japonicus) related to prey distribution and feeding in the nursery ground