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Open Access

Volume 2 Issue 3 1000114J Aquac Res Development

ISSN: 2155-9546 JARD, an open access journal

Research Article Open Access

Strand et al. J Aquac Res Development 2011, 2:3

http://dx.doi.org/10.4172/2155-9546.1000114

Research Article Open Access

AquacultureResearch & Development

Keywords: PercaFluviatilis;emperature; Body size; Growth rate; GC;Energy expenditures; DEN

Introduction

o calculate eed requirements o arm animals, approaches based

on energetic principles are requently used. For livestock, the extent o

nutritional knowledge is much more developed compared to that o sh,and there is a long tradition to utilize this knowledge or calculation o

the daily eed allowances o the animals [1,2]. Te energy requirements

o sh has traditionally been estimated by constructing complete

energy budgets, balancing energy intake against energy expenditures

such as aecal production, nitrogen excretion, metabolism and growth

[3-6]. Despite improvements in methodology, this approach is oen

associated with several potential sources o error [4,5,7,8] and many o

the developed energy budgets prove to deliver inaccurate results when

tested [9-11].

As a nal developmental stage, temperature was added to theDGC equation, resulting in the ormation o the thermal unit growthcoecient (GC, [21]). Due to the mathematical structure of the TGCcoecient and with the inclusion o temperature in the calculationof growth rate, TGC is thought to be less aected by body size of the

sh [22-24] and temperature [24-26] than SGR. In addition, the GCcoecient has been shown to predict growth over time quite accurately[21,27]. However, there are some indications that the TGC may not beas stable as previous studies have shown [28,29]. Whether the GCof Eurasian perch (from here on referred to as perch) is aected bytemperature and sh body size has not earlier been thoroughly studied.

Data on digestible energy need (DEN) of the sh can be obtained bymeasuring the digestible energy intake o sh divided by the obtainedgrowth. Te advantage with the DEN model is that since the values orthe dierent energy expenditures need not be quantied, estimates ofthe energy requirements can be made when the sh are being raisedunder normal culture conditions. As standard metabolic rate of shincreases with increasing temperature [5,30,31] so does the energyexpenditures o the sh, and hence the DEN values. Moreover, as shincreases in size, a shi in sh body composition occurs, with increaseddeposition o at in larger sh [4,5]. Te energy value o at is muchhigher compared to that o protein [3] and deposition o at also leadsto less deposition o water in the body compared to when proteins are

Abstract

To calculate the theoretical daily energy requirement of sh, information about the daily growth increment and

the amount of digestible energy needed (DEN) to obtain one unit of biomass gain is required. The thermal unitgrowth coefcient (TGC) can be used for estimation of the daily growth increment. TGC is thought to be less affected

by body size of the sh and temperature than the specic growth rate (SGR). However, there are some indications

that the TGC may not be as stable as previous studies have shown. Furthermore, according to the theoreticalbackground, DEN should increase as sh body size increases and with temperature. However, some data indicate

that the DEN for percid sh may be unaffected by both these factors. The main objectives of this study was to

estimate the effects of temperature and sh body weight on growth (TGC and SGR) and digestible energy need

(DEN) of the Eurasian perch Perca uviatilis (Linnaeus). In two separate laboratory experiments, feed intake, growthand energy expenditures were measured at either different temperatures (8.5-27.1oC) or for sh of different bodysizes (20-110g). TGC and SGR proved to be affected by temperature and body size of the sh, while DEN was only

affected by body size. The advantages with TGC for growth model construction thus seem to be less apparent thanearlier believed. Thus, for evaluation of the theoretical daily energy requirement of sh, a growth model including

both temperature and body size of sh, and an energy expenditure model including body size of sh is required.

Growth and Energy Expenditures of Eurasian Perch Perca fluviatilis

(Linnaeus) in Different Temperatures and of Different Body Sizessa Strand*, Carin Magnhagen and Anders Alanr

Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Sciences, S-901 83 Ume, Sweden

Due to the problems with the classical bioenergetics approach,

a more general method to calculate the theoretical daily energy

requirement (kJday-1) o sh was developed by Alanr et al. [12].

Te proposed model was based on two major components; one thatestimates the daily growth increment (g) o the sh and one that

calculates the amount o digestible energy needed (kJ) to obtain one

unit o biomass gain (g) o the sh.

Tere are several ways to calculate the daily growth increment

o sh. Te most commonly used estimate o sh growth is the

specic growth rate (SGR, [13]). However, as SGR is aected by both

temperature [14-17] and body size o the sh [5,18-20] data collection

or model construction is very time consuming and labour demanding.

o reduce the problem with the eect o body size when expressing

growth rate, Iwama & autz [21] developed another growth index, the

daily growth coefcient (DGC). Instead o using the logarithm o the

sh weight or calculating growth rate as SGR does, DGC uses a power

unction (W1/3). Tis mathematical adjustment o the growth coefcientprovides a better t to the actual growth pattern o the sh [20,21], and

in accordance, DGC have been ound to be more stable over a range o

body weights [22].

*Corresponding author: Department of Wildlife, Fish and EnvironmentalStudies, Swedish University of Agricultural Sciences, S-901 83 Ume, Sweden,Tel:+46907868571, Fax:+469078608162; E-mail: [email protected]

Received March 08, 2011; Accepted June 20, 2011; Published July 05, 2011

Citation: Strand , Magnhagen C, Alanr A (2011) Growth and Energy Expendituresof Eurasian Perch Perca fuviatilis (Linnaeus) in Different Temperatures and of DifferentBody Sizes. J Aquac Res Development 2:114. doi:10.4172/2155-9546.1000114

Copyright: 2011 Strand , et al. This is an open-access article distributed underthe terms of the Creative Commons Attribution License, which permits unrestricteduse, distribution, and reproduction in any medium, provided the original author andsource are credited.
http://dx.doi.org/10.4172/2155-9546.1000114http://dx.doi.org/10.4172/2155-9546.1000114

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deposited [5]. As a consequence, DEN should increase as sh body sizeincreases. However, data presented by Bailey and Alanr [32] indicatethat the DEN value of percid sh may be unaected by both these

actors. Te temperature and body size dependence o DEN or perchthus needs to be evaluated urther.

e main purposes of this study were to estimate the eects oftemperature and sh body weight on growth (TGC and SGR) anddigestible energy need (DEN) of perch. We predicted that SGR andDEN but not TGC would be aected by temperature and body size ofthe sh.

Material and Methods

Fish and rearing

In autumn 2004, young-o-the-year perch were bought rom ash hatchery (located in Sderkping: 5848N; 1634E, Sweden)

and transported to the university research acility in Ume, Sweden(63o47N; 20o17E). e juveniles were hatched from eggs collectedrom wild spawners, and the ry were habituated to dry eed beorethey were delivered to the research facility. At the research facility,the juveniles were placed in square, grey, breglass indoor tanks (0.3m3). e water used in the facility was tap water, which was aeratedand heated to approximately 17oC in the tanks. Te light regime was12L:12D, with light switched on at 07.00 and o at 19.00. During on-growing, the sh were ed with increasingly larger pellet sizes (DanaFeed, Horsens, Denmark, DAN-EX 1051, 1 mm and 1.8 mm and DAN-EX 1344, 2 and 3 mm) delivered by automatic point source feeders setto deliver eed in excess.

Experimental setup

formulated feed (DAN-EX 1344, 2 or 3 mm, 13 % fat, 44 % protein,25% carbohydrates, Dana feed, Horsens, Denmark,) in excess. e dailyeed ration was divided into two meals, at 07.00-09.00 and 18.00-19.00.

Feed waste and aeces were automatically evacuated rom the tanksdaily at pre-programmed time intervals. Te number o pellets fushedout rom each tank was counted daily. Te light regime used was 16L:8D, with light (125 lux at surface) switched on at 06.00 and o at 22.00.Flow rates to the tanks were about four litres per minute. All tanks wereseparated by black plastic sheets.

1BW is the body weight of the sh2W

1

is the initial weight of the sh3W

2is the nal weight of the sh

Table 1: Summary of the experimental conditions for the study of effects of temperature on growth (SGR and TGC), feed intake (% of BW1) and energy requirement (DEN,kJ DEg-1) of Eurasian perch (Perca uviatilis).

Te experiment regarding efect o temperature was perormedduring May to July 2005 when the sh were approximately oneyear. Te optimal temperature or growth o perch is reported to bebetween 23oC [34,35] and 26oC [36], and the temperature preerenceis considered to be 18 to 27oC [36], although growth can occur as lowas 14oC [37] to 11oC [34]. For this reason, the temperature range in theexperiment was set to between 8 and 27oC. Five diferent temperature

regimes (average temperatures SD) were used in the experiment; 8.5 0.8oC, three tanks; 12.9 0.4oC, three tanks; 18.2 0.4oC, two tanks;23.1 0.5oC, two tanks; 27.1 2.2oC, two tanks. Te temperature oeach tank was recorded continuously by temperature loggers. For tankswith high temperatures (18-27oC) the duration o the experiment wasthree weeks, and the experiment was repeated in three consecutiverounds (experimental round 1a, b and c). Tree weeks has previouslybeen demonstrated to be long enough to allow reliable recordings ogrowth o perch reared at 23oC [38]. However, as growth o the speciesin low temperatures (< 14oC) is very slow [34,37], a longer period waschosen or low temperatures in this study to provide time enoughor measurable growth to occur. In tanks with low temperatures (8and 13oC) the experiment was thus extended to our weeks and wasrepeated in two consecutive rounds (experimental round 2a and b).

Experimental rounds or both high and low temperatures were run inparallel. By having diferent duration o the experimental rounds orhigh and low temperatures, respectively, identical numbers o replicatescould be obtained or all temperatures while limiting the experimentto approximately two months. Tis was desirable in order to reduceseason related variations in growth [39,40]. Groups o eight sh wereused and initial average live weight ( SD) o the sh was 28.3 g (6.9). At the start and end o each experimental round, the eed (DAN-

welve dark green cylindrical plastic tanks (100 L) were used inthe experimental setup. Inside each tank was a plastic cone connectedto a hole in the tank bottom, creating a space (approximately 55 L)with tilting walls, thus enabling uneaten pellets to tumble down alongthe walls to the collection hole in the bottom o the tank. For moredetails regarding the experiment tanks please reer to Strand et al.[33]. An automatic point source eeder was placed above each tank.Te eeders (manuactured by Storvik AS, Norway) were set to deliver

Number of replicates

Experimentalround

DatesTemperature

categoryAverage tem-perature (oC)

Average W1

(g)2 Average W2

(g)3Number offshgroup-1

SGR, TGC, feedintake (% of BW1)

DEN

1a May 12-June 2

18 18.0 33.0 37.0 8 2 2

23 22.7 31.3 34.3 8 2 2

27 26.9 33.6 23.3 8 2 0

1b June 2- June 23

18 18.4 26.6 35.3 7 2 2

23 23.1 24.6 33.8 8 2 2

27 27.3 25.0 21.0 8 2 2

1c June 23- July 14

18 18.3 31.4 37.2 8 2 2

23 23.4 30.6 26.5 8 2 2

27 27.0 33.7 19.4 8 1 0

2a May 12-June 98 8.0 33.7 34.8 8 3 1

13 12.8 32.3 28.6 8 3 1

2b June 9-July 78 9.1 20.3 35.5 8 3 3

13 13.0 19.8 31.5 8 3 3

Total numbers of replicates 29 22

Citation:Strand , Magnhagen C, Alanr A (2011) Growth and Energy Expenditures of Eurasian Perch Perca fuviatilis (Linnaeus) in Different Temperaturesand of Different Body Sizes. J Aquac Res Development 2:114. doi:10.4172/2155-9546.1000114
http://dx.doi.org/10.4172/2155-9546.1000114http://dx.doi.org/10.4172/2155-9546.1000114http://dx.doi.org/10.4172/2155-9546.1000114http://dx.doi.org/10.4172/2155-9546.1000114

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(DAN-EX 1344, 2 mm, 13 % fat, 44 % protein, 25% carbohydrates,Dana feed, Horsens, Denmark,) in the feeders were weighed and thesh were tranquilized with 10 mgL-1 AQUACALM (MARINIL, Syndel

Laboratories Ltd., Qualicum Beach, British Columbia) and their liveweight and total length was recorded. Aer weighing, the sh werele alone in the experimental tanks or 24 hours to recover rom thehandling stress beore eeding was initiated. For transer o sh to thehighest temperature, the temperature in the 27oC tanks was lowered toapproximately 19oC when sh were introduced to the tanks and wasthen gradually increased to 27oC during the ollowing 24 hours. Newsh were used in each experimental round. Te experimental data issummarized inable 1.

Aer the temperature experiment, all sh (both sh used in theexperiment and sh not used in the experiment) were divided into twotanks, one kept at approximately 17oC and one kept at approximately12oC rom July to January. Tis was done in order to increase the body

size span among the sh o identical age in preparation or the body sizestudy. In the end o January, the temperature was increased to 17oC inthe previously cold water tank (12oC), and was then maintained at 17oCor three and a hal months until the body size experiment was started.Tis was done in order to reduce the risk o growth compensationoccurring or the sh previously held in 12oC when the experiment wasstarted. During this period (July-May), rearing conditions were similarto beore the temperature experiment.

Te body size study was perormed in the same system with thesame light, management and eeding regime settings as the temperaturestudy. Te temperature in each tank was recorded continuously bytemperature loggers and were on average ( SD) 21.1oC ( 0.6). e bodysize study was perormed during May to June 2006 in two consecutive

rounds o three weeks each, with sh at an age o approximately twoyears and between 20 and 110 g. o avoid crowding and to maintain aneven rearing density, number o sh in each group was reduced as body

size o the sh increased. In size range 20 to 50 g six sh, in size range50 to 80 g ve sh, and in size range 80 to 110 g our sh were placedin each group. e entire size range (20-110 g) was represented in each

experimental round by groups of sh with dierent average body size.Within each group, standard deviation (SD) of sh body live weight (g)was as most 2.8, but on average 1.6 g. Condition actors o the groupsranged between 0.84 and 1.04 but were in average ( SD) 0.96 ( 0.06).Average condition factors for each size category are displayed inable 2.Te same eed and weighing procedures or eed and sh was used as inthe temperature experiment. New sh were used in each experimentalround. Te experimental data is summarized in able 2.

Calculations

Te SGR [13] and GC [21] were used to calculate growth rate.SGR is expressed mathematically as:

SGR = (lnW2

lnW1) / t 100

GC is expressed mathematically as:

GC = (W2

(1/3) W1

(1/3)) / (T t) 1000

where W2

is the group average weight at time t (g), W1 is the groupaverage initial weight (g), T is the water temperature (oC) and t is theduration of the experiment (number of days).

In both experiments, eed intake was calculated as weight o theeed delivered to each tank minus the number o collected pellets romthe same tank multiplied by the average weight o one pellet. Te eedintake was then expressed as % feed intake of average sh body weightper day and per sh.

e digestible energy need (DEN: kJ DEg-1) [12] describes the

amount of digestible energy (kJ) the sh needs to ingest to increase 1 gin wet weight. Te DEN is calculated as:

DEN = (FI DE) / (W2

W1)

where FI is the average eed intake per sh during the experimentalperiod (g) and DE is the digestible energy content of the feed (kJg-1).Energy values of macronutrients (23.7, 36.3 and 17.2 kJg-1 or protein,fat and carbohydrates, respectively) were obtained from Brett & Groves(1979) [3] and apparent digestibility coecients (ADC) used wereobtained rom industry standards and were 0.87, 0.90 and 0.65 orprotein, fat and carbohydrates, respectively (pers. comm. M. Jobling).From this, the ollowing values were obtained and then used to calculatethe digestible energy content of the feed: 20.6, 32.7 and 11.2 kJg-1 orprotein, at and carbohydrates, respectively.

Fultons condition actor (K; [41]) of each group in the bodysize experiment was calculated as the average condition actor o allindividuals in a group. Te K is calculated as:

where L1

is the initial length of each sh (mm).

Statistics

Te statistical soware used was SPSS 15.0 and Minitab 15.0 orWindows. For the temperature data, one group in temperature category27oC died during the experiment and was thus excluded rom thedataset. Te resulting numbers o replicates or growth and eed intakedata in 27oC were thus ve. Moreover, despite a high eed intake, three

o the groups in temperature category 27oC demonstrated negativegrowth rates. As accurate calculation of DEN from negative growthrates is not possible, energy requirement data or these replicates had to

Experimentalround

Sizecategory

Number ofindividuals

AverageW

1

AverageW

2

K1

K2

1 20-50 6 39.9 43.3 0.9 0.9

1 20-50 6 44.8 53.1 0.9 1.0

1 20-50 6 20.7 23.3 0.9 0.9

1 20-50 5 25.2 28.3 0.9 0.9

1 50-80 5 70.4 73.6 1.0 1.0

1 50-80 5 60.9 69.4 1.0 1.1

1 50-80 5 75.4 82.7 1.0 1.0

1 80-110 4 89.6 97.1 1.0 1.0

2 20-50 6 30.8 36.4 0.9 1.0

2 20-50 5 34.3 44.3 0.9 1.0

2 20-50 6 21.5 31.3 0.9 1.1

2 20-50 6 26.0 32.6 0.8 1.0

2 50-80 5 55.5 61.3 1.0 1.0

2 50-80 5 65.2 74.2 1.0 1.0

2 80-110 4 96.1 105.1 1.0 1.1

2 80-110 4 100.9 109.0 1.0 1.0

2 80-110 4 95.1 110.1 1.0 1.0

2 80-110 4 85.1 89.5 1.0 1.0

2 80-110 4 105.4 111.5 1.0 1.0

2 80-110 4 106.4 116.1 1.0 1.1

Table 2: Summary of the experimental conditions for the study of effects of sh

body size on growth (SGR and TGC), feed intake (% of body weight) and energyrequirement (DEN, kJ DEg-1) of Eurasian perch (Perca uviatilis). W

1and W

2rep-

resents the initial and nal weight of the sh and K1 and K2 represents the average

condition factor at the start and end of the experiment.


K = W1

/ L^3 * 100 000

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For the body size data, our replicates (three rom the largest sizecategory and one from the middle size category) had to be excluded fromthe dataset due to technical problems with eeding, resulting in eedrestriction o the sh during the experiment. Te observed variations

in growth (SGR and TGC), feed intake and energy requirement (DEN)were tested statistically using univariate general linear models (GLM)with experimental round (1 and 2) as factor and average body weight

(Ln transformed) as covariate. Condition factor (K) of the sh was alsoinitially used as a covariate in the GLM analysis, but as it turned out tobe insignicant or all variables it was excluded rom urther analysis.e eect of body size on condition factor (K) of the sh was, however,evaluated using linear regression analysis with average weight (Lntransformed) as factor. e eect of body weight on growth (SGR andTGC), feed intake and energy requirement (DEN) was then evaluatedusing linear models (Y = A + B X) with average body weight (Lntransformed) as X.

Results

Temperature data

Growth rate (SGR and TGC) and feed intake (able 3) and DEN

(robust ANOVA, F4,17=6.77, P=0.002) were signicantly aected bytemperature. Tank number did not aect the results signicantly ( able3). Growth (SGR and TGC) increased with temperature from 8 to 23 oC,and was then reduced at 27oC. However, growth was only signicantlyhigher in 18 and 23oC than in 8, 13 and 27oC, but did not dier between18 and 23, or between 8, 13 and 27oC, respectively (ukey post hoctest P

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round two. Neither feed intake nor energy requirement were aectedby experimental round. Development o the linear models revealeda decreasing growth rate (SGR and TGC) and feed intake and anincreasing energy requirement (DEN) of sh with increasing bodysize (Figure 2). Furthermore, the condition factor (K) of the sh wassignicantly increased with increasing size o sh (linear regressionanalysis, F

1,18= 35, 51, P0.005) between temperature categories.

For growth rates (SGR and TGC) and feed intake, number of replicates intemperature categories 8-23oC were six and in category 27oC ve. For theenergy requirement (DEN) data, numbers of replicates were four in tempera-ture category 8 and 13oC, and six in categories 18 and 23oC.

Temperature category

-0.5

0.0

0.5

1.0

1.5

2.0

TGCandSGR

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Feedintake(%o

fbw)

8 13 18 23 27

0

25

50

75

100

125

150

175

200

DEN(kJDE/g)

a

b

c

c

d

a a

a

bb

AA A

B

B

a

a a a

b

Figure 2: Linear models of growth (SGR and TGC), feed intake (% of BW) and

energy requirement (DEN; kJ DEg-1) of Eurasian perch (Perca fuviatilis) of

different size. Average weight of the sh (g) was ln transformed in the analy-

sis. White squares ( ) represent data from experimental round one and grey

triangles ( ) represent data from experimental round two.

0.0

0.4

0.8

1.2

1.6

2.0

SGR

0.0

0.2

0.4

0.6

0.8

1.0

TGC

0.0

0.4

0.8

1.2

1.6

2.0

2.5 3.0 3.5 4.0 4.5 5.0

Feedintake(%ofBW)

Ln Weight (g)

0

5

10

15

20

25

30

35

40

2.5 3.0 3.5 4.0 4.5 5.0

DEN(kJDE/g)

Ln Weight (g)
http://dx.doi.org/10.4172/2155-9546.1000114http://dx.doi.org/10.4172/2155-9546.1000114http://dx.doi.org/10.4172/2155-9546.1000114http://dx.doi.org/10.4172/2155-9546.1000114

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data collection or growth model construction as does SGR. For perch,

the GC thus lose its advantage as a simple coecient or practical use

in aquaculture.

Te digestible energy need o perch increased exponentially

at temperatures above 23oC. Below 23oC, the relationship between

temperature and DEN are in accordance with the data presented by

Bailey and Alanr [32] on percid sh species, i.e. no clear relationship.

A positive relationship between temperature and energy expenditures

should exist [5,30,31], but the eect of metabolic costs might be too

small to detect without excessive replication. At 27oC, two groups o sh

out o the ve demonstrated very high DEN values and in the remaining

three, energy expenditures were too high to allow positive net growth

to occur. Tis supports the theory o an exponential increase in energy

expenditures when temperature exceeds the normal range o growing

temperatures [3,5,6,32]. Tus, 27oC seem to be close to the tolerance

temperature or perch o this strain.

Our prediction that DEN of perch is aected by body size was,

however, ullled. DEN o perch was ound to increase signicantly

with increasing body size, which is in contrast with the data on percid

sh presented by Bailey and Alanr [32]. However, the percid data

presented in that article is quite scattered and mainly ocuses on sea

bass Dicentrarchus labrax (Linnaeus) and sea bream Sparus aurata

(Linnaeus). In accordance with the theoretical background provided

earlier, perch seems to ollow the same pattern o increased energy

expenditures with increasing body size o sh as demonstrated or

other species such as cod Gadus morhua (Linnaeus) [45,46], several

dierent salmonid species and atsh [32].

One question that must be addressed in connection with the method

used to achieve dierent sized sh of the same age by growing themin dierent temperatures before the body size experiment is whether

this treatment caused a compensatory growth o the sh kept in the

low temperature. Most existing inormation on compensatory growth

is connected to feed restriction of the sh, and knowledge about eects

and duration o compensatory growth is quite scattered [47]. In this

study, the sh kept in low temperature between the temperature and the

body size experiments were never eed restricted. Growth compensation

may, however, have occurred aer the temperature was increased due to

the previous temperature restriction. In earlier studies o compensatory

growth aer temperature manipulation in salmonid sh, growth

compensation was complete in our [48], ten [49] and approximately

20 weeks [50]. In our study, the sh had 14 weeks to recover rom

the temperature restriction beore the body size experiment started.Tis should have allowed or growth compensation to occur and to

subside again. Growth rates o small sh during experimental round

one was in act lower than that o small sh in round two, indicating

that growth compensation due to the restricted temperature between

the experiments was not occurring at that stage. Furthermore, the

condition actors o sh in experimental round one did not increase

signicantly rom the start to the end o the round which also indicates

that no compensatory growth occurred at that point.

In the present study, small groups o sh were used (our to eight

individuals per group depending on study and treatment). Dominance

hierarchies in small groups o shes are oen established through aggressive

behaviour o dominant individuals towards subordinate individuals

[51,52]. Aggressive behaviour in small groups of perch has been observedin a ew cases [53] but oen no aggression can be observed [54]. Whether

aggressive behaviour leads to dominance hierarchies in perch is unclear.

When dominance hierarchies are established, eed intake o subordinateindividuals is reduced and energy expenditures o both dominant andsubordinate sh are increased due to aggressive acts and stress responses

[52]. In a study perormed by Strand et al. [38], sh held in small groupshad signicantly lower eed intake, but also higher eed eciency (lowerenergy expenditures) than solitary individuals. is indicates that

dominance hierarchies were not the reason or the lower eed intake o shin small groups in the study perormed by Strand et al. [38]. Furthermore,perch is a schooling species, nding security in numbers. Tus the resultsobtained by Strand et al. [38] and the social preerences o the species make

the occurrence o dominance hierarchies in the groups used in this studyunlikely. Groups of sh may also compete for limited resources. However,during the study, the sh were constantly over-ed, thus competition or

eed should not have occurred.

Rearing densities may also aect performance of cultured sh. In

this study, rearing densities were deliberately maintained low (2-5 kg

m-3 in the temperature study and 3-8 kg m -3 in the size study) to avoidcrowding and water quality deterioration. In the size experiment the

size classes and the number o sh included in the groups in each size

class were designed to produce an even rearing density o sh in the

experimental tanks and to reduce the risk o crowding when large sh

were used. Tereore the number o sh per tank had to be reduced

as size o the sh increased. Furthermore, in the study perormed by

Strand et al. [38], sh held in groups of 4 and 12 individuals (2-6 kg

m-3) demonstrated high growth rates, thus the rearing densities used

in this study was sucient to provide adequate conditions or good

growth o the sh.

In the temperature experiment, growth rates and eed intake

increased, and energy requirement decreased, rom the rst

experimental round to the nal round. Te same trend could be noted

for growth of perch in the body size experiment. As both experiments

were perormed during late spring and early summer, the increase in

eed intake and growth with time may be the result o a release o a

winter suppression o appetite and growth. Similar seasonal increases

in eed intake and growth at constant temperatures have previously

been noted or perch [39,40]. Nevertheless, the main results regarding

the eect of temperature and body size on the growth, feed intake, and

energy requirements of juvenile perch are not aected by the dierences

between the rounds.

In conclusion, the prediction that GC o perch would be

unaected by temperature and body size was not fullled. TGC proved

to be signicantly aected both by temperature and body size of the shin a similar manner as is SGR. Te advantages with GC or growth

model construction thus seem to be less apparent than earlier believed.

In contrast, DEN was predicted to be aected by both temperature and

body size of the sh, but was only found to be signicantly aected by

body size. DEN was not aected by temperature at or below optimal

temperatures or growth, but as temperature increased urther, energy

expenditures seemed to increase exponentially.

Acknowledgment

We thank Eastern Norrbotten Research Station for providing nancial

support for this project and Carl Tryggers Foundation for nancial support to the

experimental setup. We also thank Andreas kerstrm for valuable comments on

the manuscript.

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