2006) 249–256www.elsevier.com/locate/aqua-online

Aquaculture 257 (

Oxygen consumption of newly settled summer flounder,Paralichthys dentatus (Linnaeus, 1766)

Robin S. Katersky a,1, Myron A. Peck b, David A. Bengtson a,⁎

a University of Rhode Island, Department of Fisheries, Animal and Veterinary Sciences, Kingston, RI 02881 USAb Institute for Hydrobiology and Fisheries Research, University of Hamburg, Olbersweg 24, D-22767, Hamburg, Germany

Received 27 October 2005; received in revised form 17 February 2006; accepted 24 February 2006

Abstract

The timing of larval metamorphosis in summer flounder, Paralichthys dentatus, from the same cohort (i.e., siblings with thesame parents) and among cohorts (different parents) is variable due to large differences in individual growth rates. In an effort tounderstand the energetic basis for growth rate differences, rates of routine (RR) and specific dynamic action (RSDA) respiration (μgO2/fish/h) were measured in groups of newly metamorphosed summer flounder and compared among fish of different sizes (15, 20,25 and 30 mm total length, TL) and between fast- and slow-growing fish from five cohorts each having a different set of parents.Although rates of RR significantly increased with increasing fish size (RR=3.02±1.04 DM0.88 ± 0.12, they were not significantlydifferent between the fastest and slowest growing fish within a cohort. Respiration rates rapidly increased during feeding and themean±SD peak RSDA was 1.91±1.29 ·RR. The mean±SD energy loss due to RSDA was 15.6±11.5% of the ingested prey energy.Differences in RSDAwere noted among fish of different sizes and between fast- and slow-growing fish. However, the results of thisstudy suggest that the energetic basis for growth differences among summer flounder appears to result from processes related toenergy intake (e.g., food consumption) rather than those related to routine or feeding energy loss.© 2006 Elsevier B.V. All rights reserved.

Keywords: Summer flounder; Paralichthys dentatus; Oxygen consumption; Specific dynamic action; Growth rate

1. Introduction

Summer flounder, Paralichthys dentatus (Linnaeus,1766), is a left-eyed flatfish belonging to the familyBothidae that inhabits the continental waters fromMaine to South Carolina, USA (Collette and Klein-MacPhee, 2002). This species is economically important

⁎ Corresponding author. Tel.: +1 401 874 2668; fax: +1 401 8747575.

E-mail address: Bengtson@uri.edu (D.A. Bengtson).1 Current Address: University of Tasmania, Tasmania Aquaculture

and Fisheries Institute, School of Aquaculture, Locked Bag 1-370,Launceston, Tasmania 7250, Australia.

0044-8486/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.aquaculture.2006.02.062

to fisheries fromMassachusetts to South Carolina wherecommercial landings of∼ 6300 t were valued at over US$21 million in 2002 (personal communication, Natio-nal Marine Fisheries Service, Fisheries Statistics andEconomic Division, Silver Spring, MD, USA). In recentyears, a small industry has begun intensively culturingthis species in the northeast USA (Bengtson, 1999)and research efforts have focused on understandingthe factors that affect early growth and survival (e.g.,Schreiber, 1998; Alves et al., 1999; Francis and Beng-tson, 1999; Gavlik et al., 2002) to increase the efficiencyof aquaculture.

Growth of an organism is based on the utilization ofavailable energy to increase body tissue. Energy gained

250 R.S. Katersky et al. / Aquaculture 257 (2006) 249–256

from food consumption may also be used for processesother than growth. Studies in bioenergetics at theindividual level deal with the partitioning of ingestedfood energy based on a balanced energy budget:

C ¼ Gþ Rþ E þ F

where C=consumption of food energy, G=growth,R=respiration, E=excretion (nitrogenous wastes) andF=fecal output (Brett and Groves, 1979; Jobling, 1994;Day et al., 1996). Rates of respiration by fish have beenclassified into different levels based upon the activityoccurring during the measurements. These levels includestandard (RS), routine (RR), specific dynamic action(RSDA) and active (RA) respiration rates which corre-spond to the energy expended due to basal metabolism(e.g., anaesthetized fish), routine movements, feeding,digestion and assimilation of food, and active swimming,respectively (Brett and Groves, 1979). RSDA has threecomponents that are of interest: the peak value (SDApeak)represents the highest O2 consumption rate, the duration(SDAdur) is the time required for O2 consumption rates toreturn to baseline (pre-feeding) levels, and themagnitude(SDAmag) is the total O2 consumed above the baselinelevel during the SDA period (Jobling and Davis, 1980).

Determining the energy budget parameters for fishmay help identify the physiological mechanisms affectingintra-specific variation in growth rate. For example, Cuiand Liu (1990) examined the bioenergetics of juveniles ofsix fish species and concluded that intra-specific diffe-rences in growth rates were influenced by differences inthe proportion of energy allocated to metabolism, diffe-rences in the amount of food consumed or a combinationof both factors, depending on species. Intra-specificdifferences in growth rates are often most marked duringthe larval period and have been previously examined inflatfish species (Chambers and Leggett, 1987; Gavliket al., 2002). Chambers and Leggett (1987) reported thatlarval winter flounder, Pseudopleuronectes americanus,that metamorphosed first had higher growth rates thanthose that metamorphosed later and that these growth ratedifferences continued into the juvenile stage. Althoughrecent studies on juvenile fish suggest a relationshipbetween inter-individual differences in metabolic rate(respiratory and exercise physiology) and growth rate infathead minnows, Pimephales promelas (Kolok and Oris,1995), Atlantic salmon, Salmo salar (Cutts et al., 1998),rainbow trout, Oncorhynchus mykiss Gregory and Wood,1998) and Atlantic cod, Gadus morhua (Peck et al.,2004), similar studies have not yet been conducted usingsummer flounder.

The purpose of the present study was to quantify intra-cohort (i.e., siblings with the same parents) differences in

RR and RSDA for fast- and slow-growing summer flounderduring the period immediately after metamorphosis. Foursizes of fish were examined (15, 20, 25, 30 mm totallength, TL) in each of five separate cohorts. Assumptionsincluded that (1) growth rate differences observed amonglarvae continued into the juvenile stage, and (2) the largestenergetic differences would be observed in a comparisonof the fastest and slowest growing fish.

2. Materials and methods

2.1. Fish culture

Broodstock summer flounder were collected fromLong Island Sound, USA, and maintained at theUniversity of Rhode Island. Fertilized eggs were obtainedfrom five pairs of one male and one female summerflounder each, with the offspring from each cross referredto as a cohort. Each cohortwas reared separately. The eggshatched and the larvae were reared in semi-static 189-Laquaria (25% water renewal/d, 20-μm-filtered, UV-sterilized seawater, 30‰, 20±1 °C) with a 16L:8D lightregime according to the methods of Bisbal and Bengtson(1993) and Alves et al. (1999). As the fish grew and whenintra-cohort differences in fish size became apparent(∼ 40 days post hatch), larvae were separated into threegroups by grading the fish, i.e. removing the largest fishfrom the common rearing tank, as they metamorphosedand settled to the aquarium bottom. Graded fish wereplaced into separate 75-L flow-through aquaria at 20±1 °C. Grading of settled fish occurred once a week forthree weeks, resulting in three groups: grade 1 (G1, fast-growing larvae, first settling juveniles), grade 2 (G2,medium-growing larvae, later settling juveniles), andgrade 3 (G3, slow-growing larvae, last settling juveniles).Fish from G1 and G3 were used in this study. Fish werefed enriched (DHA Selco, INVE Aquaculture) brineshrimp, Artemia sp., nauplii (Great Salt Lake, Utah,strain) twice daily. Fishwere sampled from the G1 andG3groups for respiration measurements as they reached thesizes of 15, 20, 25, and 30 mm TL (± 1 mm for each sizeclass).

2.2. Experimental protocol

Rates of routine (RR) and SDA (RSDA) respirationwere measured during 48-h experiments. The G1 andG3 fish from five separate cohorts were examined,except that insufficient numbers of G1 fish existed forcohorts 1 and 3 to test all fish sizes (Table 1).

Respiration rates were measured in an automated, flow-through respirometer at a temperature of 20±1 °C and a

251R.S. Katersky et al. / Aquaculture 257 (2006) 249–256

light intensity of 4.80–5.10 μmol/s/m2 (16L:8D photope-riod). Each trial had at least four 0.75-L respirationchambers, three with fish and one serving as a controlchamber without fish (except 20-mm fish in cohort 2, onlytwo replicates with fish). Fish were placed in the chambersand allowed to acclimate overnight. All chambers wereidentical with clear plastic lids to allow light into thechamber, however the chambers were positioned within alarger tank to shield them from each other as well asexternal disturbances. The number of fish in each chamberdepended on fish size to maintain a similar biomass withinchambers across experiments (i.e., when workingwith fishof different sizes) (Table 1). Water flowed through eachchamber andwas redirected past an oxygenmicroelectrode(MI 730, Microelectrodes, Inc., USA) in sequential five-minute intervals. With four chambers running, a measure-

Table 1Summary data for respiration trials using groups of newly settled summer flogrades (see text for explanation of grade)

Cohort Grade(1, 3)

Nominallength (mm)

Measuredlength (mm)

Dry mass(mg)

1 3 15 14.24 (0.71) 5.16 (0.91)1 3 20 20.06 (0.69) 12.69 (1.85)1 3 25 24.79 (0.72) 26.47 (2.48)1 3 30 29.59 (0.60) 43.12 (2.67)2 3 15 14.85 (0.50) 5.43 (0.54)2 3 20 19.91 (0.55) 13.01(1.09)2 3 25 25.05 (0.60) 25.85 (1.84)2 3 30 29.73 (0.57) 43.07(2.46)2 1 15 14.59 (0.41) 5.14 (0.44)2 1 20 19.93 (0.57) 13.05(1.13)2 1 25 24.94 (0.67) 25.49 (2.05)2 1 30 29.74 (0.74) 43.16 (3.19)3 3 15 14.69 (0.71) 4.57 (0.61)3 1 15 14.56 (0.58) 4.84 (0.59)3 1 20 20.18 (0.81) 12.89 (2.14)3 1 25 25.19 (0.81) 26.65 (3.15)3 1 30 29.71 (0.90) 42.08 (5.11)4 3 15 14.59 (0.85) 4.75 (1.36)4 3 20 19.79 (0.75) 12.80 (1.92)4 3 25 24.50 (0.60) 25.57 (2.82)4 3 30 30.21 (0.63) 49.81 (3.23)4 1 15 14.65 (0.75) 5.10 (0.90)4 1 20 19.81 (0.64) 12.88 (1.63)4 1 25 24.89 (0.77) 26.40 (3.85)4 1 30 29.81 (0.84) 47.84 (4.25)5 3 15 14.36 (0.52) 4.66 (0.54)5 3 20 20.12 (0.81) 11.69 (2.62)5 3 25 25.33 (0.41) 25.96 (1.64)5 3 30 27.09 (1.10) 30.99 (4.35)5 1 15 14.59 (0.66) 5.10 (0.67)5 1 20 20.18 (0.52) 14.07 (1.38)5 1 25 25.34 (0.80) 29.11 (3.19)5 1 30 29.79 (0.79) 38.99 (2.77)

Values are presented as mean (±SD).

ment was made on each chamber every 20 min. Winklertitrations allowed microelectrode units (% oxygen) to beconverted to O2 concentration (mg O2/L). After the initialacclimation period, respiration measurements were madefor a total of 48 h. After the initial 24 h, a ration of liveArtemia naupliiwas supplied to the fish in the experimentalchambers in order to measure feeding respiration, RSDA. Aration was also supplied to the control chamber in order todetermine the contribution of the liveArtemia nauplii to thetotal respiration of the chambers with fish. At the end ofeach trial, individual TL (± 0.1 mm) and dry mass (DM, ±0.1 mg) were measured for a random subsample of fishfrom each chamber (Table 1). Fish TLwasmeasured usingcomputer image analysis (Optimus TM Image AnalysisSoftware/Sony CCD Camera) and DM was determinedafter drying in an oven at 60 °C for N 48 h.

under (Paralichthys dentatus) from each of 5 cohorts and two different

N(chambers/trial)

Fish/chamber Fish sampled fordry mass (n/chamber)

3 50 73 20 53 10 44 8 83 42 102 20 103 12 43 10 103 37 102 21 103 15 42 8 84 54 104 55 102 25 83 10 53 8 53 52 ­3 25 103 10 53 8 24 55 103 23 53 10 53 8 53 52 53 20 52 10 32 8 53 55 72 20 53 11 33 8 5

252 R.S. Katersky et al. / Aquaculture 257 (2006) 249–256

Rates of O2 consumption (R, mg O2/fish/h) were cal-culated as follows:

R ¼ UOC−OF þ s dOF

dt

� �

n

where OC=the concentration of oxygen (mg O2/L) in thecontrol chamber (without fish), OF=the concentration ofoxygen in a chamber with fish, Φ=the flow rate (L/h),n=the number of fish in the test chamber, τ=the flushingtime of the chamber (h)=(chamber volume (0.75 L)) /Φ and (dOF /dt) is the rate of change in the [O2] with time(t), followingNorthby (1976). TheRRwas calculated as themean of measured R during the 24-h period prior tofeeding.

The SDApeak was the maximum rate above RR,usually measured shortly after feeding. The SDAdur wasequal to the time (h) elapsed between feeding and thedecrease in R to pre-feeding (RR) levels. The magnitudeof RSDA (SDAmag) (mg O2/fish) was calculated as:

SDAmag ¼X

½ðRelevated−RRÞtS�where R(elevated) =elevated rates of O2 consumptioncompared to RR and tS is the amount of time (h) bet-

Table 2The ration (percent fish dry mass, % DM), actual and corrected values of SDAsummer flounder, Paralichthys dentatus

Cohort Grade(1, 3)

Size(mm)

Ration(%DM)

SDAmag (μg O2

SDAactual

1 3 15 5.21 75.66 (53.11)1 3 20 6.78 132.29 (32.96)3 1 15 4.85 76.45 (18.94)3 3 15 3.41 22.88 (4.03)3 3 20 4.11 56.74 (19.94)3 3 25 5.22 264.91 (71.71)3 3 30 4.47 152.29 (27.92)4 1 15 4.37 25.30 (18.22)4 3 15 3.96 27.53 (4.44)4 1 20 4.87 86.31 (35.26)4 3 20 3.86 56.74 (19.94)4 1 25 4.73 183.63 (71.60)4 3 25 5.48 167.94 (55.06)4 1 30 3.37 401.75 (48.01)4 3 30 3.92 289.29 (27.92)5 1 15 4.67 50.85 (5.38)5 3 15 5.52 70.45 (15.45)5 1 20 5.95 69.29 (33.10)5 3 20 6.17 163.86 (25.24)5 1 25 11.64 552.93 (118.59)5 3 25 7.35 281.00 (25.92)5 1 30 3.49 208.54 (206.96)5 3 30 3.39 83.12 (27.52)

Values are presented as mean (±SD).

ween samples. The analysis of RSDA contains data onlyfrom cohorts 1, 3, 4 and 5 because the ration supplied tocohort 2 was not quantified.

Ration levels differed among the trials and were shownto have a significant effect on SDAmag (FG1=22.436,df=1,26, pb0.001; FG3=22.972, df=1,40, pb0.001) andSDApeak (FG1=11.792, df=1,26, p=0.002; FG3=8.506,df=1,40, p=0.006). However, there was not a significanteffect on the SDAdur (FG1=0.799, df=1,26, p=0.380;FG3=2.534, df=1,40, p=0.119). In order to compare themagnitude of SDA values, rates were normalized to themean ration size provided for each size class. Values werecorrected according to the following steps: (1) for each sizeclass of either G1 or G3, a linear regression was calculatedfor the relationship between ration size and SDA, (2) usingthat linear regression equation, the expected value of SDAwas calculated for the actual ration and the mean rationsize, and (3) a corrected value of SDA was calculatedaccording to the formula:

SDAcorrected ¼ SDAactual þ ðSDAMRðcalcÞ−SDAARðcalcÞÞwhere SDAcorrected=corrected value of SDAmag orSDApeak; SDAactual=SDAmag or SDApeak for the actualration provided; SDAMR(calc) =SDAmag or SDApeak

mag and SDApeak for each cohort, grade and size tested of newly settled

fish/h) SDApeak (μg O2 fish/h)

SDAcorrected SDAactual SDAcorrected

65.05 (53.11) 22.00 (0.03) 16.69 (0.26)46.76 (32.96) 55.12 (1.45) 12.36 (14.54)124.03 (18.94) 27.73 (0.22) 39.63 (2.25)117.22 (4.03) 29.59 (0.45) 76.76 (4.54)79.59 (19.94) 62.96 (1.03) 74.38 (10.32)283.10 (71.71) 123.83 (2.20) 132.93 (21.96)124.33 (41.89) 193.48 (3.61) 194.79 (17.60)69.54 (18.22) 27.85 (0.36) 38.91 (3.59)76.75 (4.44) 34.16 (0.32) 58.77 (3.20)82.13 (35.26) 71.48 (1.10) 70.43 (10.96)121.07 (12.97) 52.05 (1.06) 61.15 (10.55)233.88 (71.60) 109.39 (1.64) 121.95 (16.43)139.33 (55.06) 128.87 (1.69) 132.93 (21.96)447.33 (48.01) 154.87 (1.13) 166.26 (11.31)250.77 (27.92) 234.64 (0.57) 215.37 (5.66)92.43 (5.38) 27.85 (0.36) 38.24 (1.93)79.97 (15.45) 32.67 (0.58) 37.43 (5.81)86.07 (33.10) 33.49 (0.16) 37.68 (1.62)136.26 (25.24)] 94.66 (1.88) 80.86 (18.82)235.10 (118.59) 205.91 (0.96) 126.45 (9.61)195.47 (25.92) 173.98 (6.01) 130.21 (60.12)285.04 (206.96) 179.22 (3.58) 198.35 (35.79)132.23 (27.52) 170.24 (1.76) 194.79 (17.60)

Rou

tine

Res

pira

tion

Rat

e (m

g O

2 / f

ish/

h)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

10 15 20 25 30 35

1 G32 G32 G13 G33 G14 G34 G15 G35 G1

A)

0.00

0.02

0.04

0.06

0.08

0.10

0.12B)

0 10 20 30 40 50 60

Total Length (mm)

Dry Mass (mg)

r2= 0.87

n= 97

r2= 0.85

n= 97

253R.S. Katersky et al. / Aquaculture 257 (2006) 249–256

calculated for the mean ration provided; SDAAR(calc)

=SDAmag or SDApeak calculated for the actual rationprovided. The values were calculated using the linearregressions for SDAmag on ration size for each size class.The SDAcorrected and SDAactual values as well as rationlevel data for SDAmag and SDApeak can be found inTable 2.

The energy loss in Joules (J) due to O2 consumptionwas calculated using the following conversion factors:1 mg O2=3.25 cal (Brett and Groves, 1979) and1 cal=4.184 J.

2.3. Statistical analysis

To determine the effects of fish size class [fixed factorwith four levels, 15, 20, 25 and 30 mm size classes], grade[fixed factor with two levels, G1 and G3] and cohort[random factor because this provided a measure ofvariability among groups of fish] on RR and RSDA athree-way mixed model ANOVA was used. Differenceswere considered significant at pb0.05 and significantdifferences were compared using a Tukey post hoc test.Data analyses were conducted using SPSS software(version 11.5). This study utilized TL (mm), and sincerespiration rates are clearly affected by mass, the rela-tionship between DM and TL was compared amongcohorts using an ANCOVA.

3. Results

3.1. Weight and length

The relationships between TL (mm) and DM (mg)were not significantly different among the 5 cohorts

10 15 20 25 30 350

10

20

30

40

50

60Cohort 1Cohort 2Cohort 3Cohort 4Cohort 5

R2= 0.994n= 97

Total Length (mm)

Dry

Mas

s (m

g)

Fig. 1. The relationship between total length (mm) and dry mass (mg)pooled from the five cohorts tested for newly settled summer flounder,Paralichthys dentatus.

Fig. 2. The relationships between total length (mm) and dry mass (mg)with the routine respiration rate (mg O2/fish/h) of newly settledsummer flounder, Paralichthys dentatus, for each cohort and gradetested. Grade 1 (G1) are represented by open symbols and grade 3 (G3)are closed symbols.

examined (ANCOVA, p=0.67). The pooled relationshipfor all five cohorts used in this study (Fig. 1) was equalto:

DM ¼ 0:0013ðF0:0002ÞTL3:06ðF0:04Þ

ðR2 ¼ 0:99; n ¼ 97Þ:

3.2. Routine respiration

RR was significantly increased with increasing fishsize (Fsize=101.08, df=3,11, pb0.001); however, ratesof RR between G1 and G3 fish did not differ

254 R.S. Katersky et al. / Aquaculture 257 (2006) 249–256

significantly (Fgrade=0.301, df=1,3, p=0.625). There-fore, the RR data from all cohorts and growth rates werepooled and the effect of flounder size on RR wasdescribed by:

RR ¼ 0:01ðF7:2−4ÞTL2:69ðF0:25Þ

RR ¼ 3:02ðF1:04ÞDM0:88ðF0:12Þ

where RR=μg O2/fish/h, TL=mm, and DM=mg(Fig. 2).

3.3. Specific dynamic action

The rate of respiration increased during feeding withthe mean±SD SDApeak being 1.91±1.29 (n=68) timesthe pre-feeding routine rate. No significant differenceswere found in SDApeak between G1 and G3 fish(Fgrade=0.541, df=1,2, p=0.543), however significantdifferences were found among fish size classes(Fsize=6.220, df=3,6, p=0.026). The 15 mm sizeclass had significantly higher peaks than the remainingsize classes. The mean (± SD) SDAdur was 9.3 (± 3.18,n=68) h. No significant differences in SDAdur werefound between G1 and G3 fish (Fgrade=7.457, df=1,1,p=0.268) or among fish in different sizes classes(Fsize=0.428, df=3,7, p=0.739).

Significant differences in SDAmag were observedbetween G1 and G3 fish and among the different sizeclasses (Fgrade * size class=27.952, df=3,3, p=0.011). The

Total Length (mm)

SD

A m

agni

tude

(m

g O

2 / f

ish)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

15 20 25 30

G1

G3

a a a a

b b

c ab

Fig. 3. The SDAmag (mg O2/fish) for grade 1 (G1,■) and grade 3 (G3,□) newly settled summer flounder, Paralichthys dentatus, for each sizeclass tested. Significant differences between size class and grade arerepresented with different letters. Values are presented as mean±SD.

significant difference between the G1 and G3 fish wasfound for fish in the 30 mm size class. No differenceswere found between the 15- and 20-mm size classes andthe 30-mm G3 fish. Significant differences were foundbetween the 15- and 20-mm size classes and the 25- and30-mm (G1) fish (Fig. 3).

4. Discussion

The present study was the first to examine rates ofoxygen consumption in newly settled summer flounderand evaluated whether differences in either routine orfeeding metabolism were associated with intra-cohortdifferences in growth rates. Results of this studysuggested that groups of the fastest and slowest growingmembers of a cohort had similar rates of routinerespiration. Simlick et al. (2000) observed that differ-ences in growth rate apparent among pre-metamorphiclarvae were absent after metamorphosis when the fishwere graded and subsequently raised separately as, i.e.,G1 fish, although always larger than the G3 fish, hadsimilar post-metamorphic growth rates. Thus, our initialassumption that differences in growth rate in the larvalstage are carried into the juvenile stage appears not to becorrect. It may be that differences in metabolic losseswill be found in pre-metamorphic larvae wheredifferences in growth rate are apparent; however, thepresent study does not indicate that aquaculturists coulddevelop any particular strategies for flounder culturebased on differences in oxygen consumption amongnewly settled juveniles.

Recent studies suggest that the effect of body size onrates of respiration change with body size (Bochdanskyand Leggett, 2001), and that rates of respiration scaleisometrically (b=1 in R=aDMb) in larvae (e.g., Cettaand Capuzzo, 1982; Rombough, 1988; Day et al., 1996)and allometrically (bb1) in larger juveniles and adults(Oikawa et al., 1991; Jobling, 1994; Post and Lee, 1996).The previous studies comparing metabolic scaling atdifferent fish sizes did not consider flatfish species. In thepresent study, rates of RR in newly metamorphosedflounder juveniles increased with increasing bodyweight by an allometric scaling factor (b-value) of0.88. Only one other study to date has been conducted onthe metabolism of juvenile summer flounder (20–40 g)and a lower scaling factor (0.83) was determined (Wanget al., 2004). Unfortunately there are no comparable dataon newly settled juvenile flounder of other species,however a comparison of results for larger juveniles andadults suggests that this trend of decreasing b-values alsoexists in flatfish. Voyer andMorrison (1971) calculated amass exponent (b-value) of 0.79 for juvenile winter

255R.S. Katersky et al. / Aquaculture 257 (2006) 249–256

flounder (11.5–32.3 g). Studying 1–326 g juvenileplaice (Pleuronectes platessa), Fonds et al. (1992) founda mass exponent of 0.71. Similar mass exponents (0.69to 0.71) were estimated for ∼ 2–1000 g turbot(Scophthalmus maximus) in two separate studies(Brown et al., 1984; Waller, 1992).

The increase in respiration rates observed during andshortly after feeding is thought to be primarily due toincreased rates of protein synthesis (Lyndon et al., 1992;Carter and Houlihan, 2001). In the present study, themean±SD SDApeak rate was 1.91±1.29 times greaterthan the routine rate. Jobling and Davis (1980) found thepeak rate for plaice to be approximately twice the pre-feeding rate and that the peak rate increased withincreasing ration size. However, in this study, there wasno significant effect of ration size on the SDApeak.Species-specific differences exist in the relative increasein rates of respiration after feeding. For example, althoughthe SDApeak appears to be close to 2 in sedentary flatfishspecies (Jobling and Davis, 1980; Jobling, 1981; thisstudy), the SDApeak is lower (between 1.57 to 1.75 greaterthanRR) inmore active, roundfish species such as channelcatfish, Ictalurus punctatus (Brown and Cameron, 1991)blenny, Blennius pholis (Vahl and Davenport, 1979) andyoung juvenile cod, Gadus morhua, (Peck et al., 2003).The duration of SDA has been shown to be affected byration level (Vahl and Davenport, 1979; Jobling andDavis, 1980; Peck et al., 2003); however, that was not thecase in this study.

The amount of energy lost via SDAmag, generallyexpressed as a percentage of ingested or absorbed energy(Jobling, 1981), can be influenced by the size of the ration(Vahl and Davenport, 1979; Jobling and Davis, 1980; thisstudy). In the present study, the mean±SD SDAmag was15.6±11.5% of the ingested energy or 33.1±26.1% of theabsorbed energy, based on a food absorption efficiency of79.1% (energy content basis) for similar-sized summerflounder feeding on the same diet (Getchis and Bengtson,2006). Similar SDAmagnitudes have been found in otherstudies using flatfish (Vahl and Davenport, 1979; Joblingand Davis, 1980; Jobling, 1981).

In conclusion, results of this study indicated that onlysubtle differences existed in the rates of routine andfeeding energy loss between G1 and G3 fish and nodifferences were observed among cohorts. Greaterdifferences were observed both between fish grades andamong cohorts for food consumption by similar-sized fishin counterpart experiments to those reported here (Getchisand Bengtson, 2006). The data in these two studies, alongwith data on ammonia excretion (Katersky, 2000),provide the information on energy intake and energyexpenditures required to parameterise a balanced energy

budget for newly settled summer flounder which willallow a more detailed examination of the physiologicalbasis for differences between G1 and G3 fish.

Acknowledgements

We thank Jennifer Specker and Grace Klein-MacPhee for their helpful comments on this manuscript;William Macy for the use of the image analysis system;Natalie Moltschaniwskyj for statistical assistance; TessaL. Simlick for help with larval rearing and experiments;Steve Gavlik and Brad Bourque for help in the lab.Technical support was provided by Jeffrey Greenburg ofthe U.S. Environmental Protection Agency NHEERL,Atlantic Ecology Division. This research was supportedby The National Sea Grant College Program underGrant No. NA86RG0076.

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