Directory UMM :Data Elmu:jurnal:A:Aquaculture:Vol184.Issue1-2.Apr2000:

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www.elsevier.nlrlocateraqua-online

European sea bass growth and N and P loss under

different feeding practices

M. Paspatis

a,)

_{, T. Boujard}

b

, D. Maragoudaki

c

, M. Kentouri

a,c

a

Institute of Marine Biology of Crete, P.O. Box 2214, GR-71003 Iraklion, Crete, Greece

b

Station d’ Hydrobiologie, INRA, Saint-Pee-Sur-Ni´ Õelle, F-64310, France c

Department of Biology, UniÕersity of Crete, P.O. Box 2208, GR-71409, Iraklion, Crete, Greece

Accepted 13 September 1999

Abstract

This study was performed to assess growth rate, feed efficiency, and N and P loss of sea bass

Žinitial body weight 3.5 g , held in 500-l tanks under ambient temperature and natural light, and.

fed according to the following methods: by automatic feeders that released feed continually in

Ž .

daylight according to feed manufacturers’ recommendations AF100% ; half of the above

continu-Ž . Ž .

ally in daylight AF50% ; half of the above again but in two meals only AF50%M ; and by

Ž . Ž . Ž .

self-feeders that supplied feed at low SFL , medium SFM and high SFH reward. None of the feeding conditions affected the survival rate of fish. SFL fish had the highest specific growth rate, while AF50% and AF50%M the lowest. Population weight distribution in the restricted

automatic-Ž .

fed fish AF50% and AF50%M was more homogenous compared to the other feeding conditions.

Ž .

These two practices produced high feed efficiency ratios 0.93 and 0.95, respectively , compared

Ž . Ž .

to the AF100% 0.57 and self-fed ones SFL: 0.60; SFM: 0.37; SFH: 0.21 . Self-feeding at low reward of 0.6 g triggery1_{could be considered as the optimum feeding practice, combining higher}

weight gain, lower N and P loss, and intermediate feed supply compared to the other treatments. In the SFH method, fish did not adjust their manipulation of the self-feeders according to their feed needs. Daily feeding activity in all self-fed fish groups was independent of feeding reward.

Keywords: Growth; Feeding; Nitrogen; Phosphorus; Waste; Sea bass; Dicentrarchus labrax

Ž .

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( ) M. Paspatis et al.rAquaculture 184 2000 77–88 78

1. Introduction

Successful feeding of intensively cultured fish species requires detailed knowledge of which nutritional requirements and feeding practices best contribute to the improvement of rearing in terms of growth rate and feed efficiency. In sea bass, Dicentrarchus

labrax, one of the most popular and highly produced species in the Mediterranean

region, improvement of feeding is one of the main priorities of farmers because the cost

Ž .

of feed accounts for up to one-third of running expenses Stefanis, 1995 . Despite this, Ž

investigation of feeding practice in sea bass is limited Tsevis et al., 1992; Boujard et al., .

1996; Azzaydi et al., 1998 , compared to the abundant literature on the effect of feed Ž

composition on the growth of this species Carrillo et al., 1986; Tibaldi et al., 1991; Santulli et al., 1993; Ballestrazzi et al., 1994; Garcia-Alcazar et al., 1994; Perez et al.,

´

. 1997; Diaz et al., 1998 .

Ž

Ration size Reddy et al., 1994; Ryer and Olla, 1996; Fontaine et al., 1997; Azevedo .

et al., 1998 has been shown to be essential in fish fed daily with a fixed amount of feed. In the case of free access to feed, as in self-feeding, the determinant factor of feed

Ž

efficiency is the reward level, i.e., the instant ration per self-feeder actuation Alanara,

¨ ¨

.

1996 . None of the parameters have been studied thoroughly in sea bass, although fixed feeding mainly by automatic feeders, is used empirically and self-feeding is a promising

Ž

feeding method for sea bass culture Kentouri et al., 1986; Anthouard et al., 1993; .

Divanach et al., 1993; Boujard et al., 1996; Azzaydi et al., 1998 . According to Paspatis

Ž .

et al. 1999 , sea bais juveniles, when fed by self-feeders are fed to satiation and exhibit similar growth and feed efficiency to fish fed by hand.

The improvement of feeding is not only a priority because of the cost of feed, but also because, given the rapid development of fish farming in the world, a better knowledge of waste output is crucial so that aquaculture be environmentally sustainable ŽCho and Bureau, 1998; Kaushik, 1998 . This is especially important in the case of open. sea farming using cages, as is the case for the majority of sea bass farms. Under such conditions, uneaten feed and faecal and metabolic losses have a direct impact on the environment. The effect of dietary composition on nutritional waste of sea bass has been

Ž

studied by several authors Ballestrazzi et al., 1994; Dosdat et al., 1996; Diaz et al., .

1998; Kaushik, 1998 , but the effect of feeding practice on waste production has apparently never been studied in this species.

This study was conducted to determine the effect of different feeding practices Ž_{different automatic feeding protocols and self-feeding with different feed rewards on}.

Ž .

growth, feed efficiency ratio FER , and N and P loss in sea bass juveniles. In addition, daily feeding activity in self-fed fish was investigated to define the consequences of feed rewards on fish feed demands.

2. Materials and methods

Ž .

Sea bass juveniles initial weight 3.5 g were obtained from broodstock kept in the open installations of the Institute of Marine Biology of Crete, Greece. They were

Ž

transferred to indoor cylindrical tanks of 500-l at initial stocking density of 50 fish

y1_. _Ž _. _Ž

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the beginning, dawn was at 0520 h with 14 h daylight; at the end, dawn was at 0630 h

. y1

with 11 h daylight . Sea water flow to each experimental tank was 24 l min through a Ž

semi-recirculated system equipped with a biological filter 75% of water was renewed

. Ž .

daily . Commercial feed BIOMAR, France was used throughout the experiment. Two

Ž .

types of feed Biomar, Aquastart 15 No. 4 and Ecolife 17 No. 2 were supplied according to the manufacturer’s recommendations.

Fish were acclimated to the experimental conditions for 2 weeks. At the beginning of the experiment, they were deprived of food for one day, weighed individually and divided equally into tanks so as to have a similar population structure. Six feeding regimes were applied in triplicate. Three fish groups fed by automatic feeders were subjected to the following feeding levels: feed manufacturer’s recommendations Ž_{AF100% every 15 min during daylight; half of the recommended feed AF50% every}. Ž .

Ž 15 min during daylight; half of the recommended feed in two meals of 3 h each 3 h

. Ž .

after dawn and 3 h before the dusk AF50%M . The duration of feed distribution was adjusted to daylight changes every 2 weeks. Three additional fish groups were fed by

y1_Ž

means of self-feeders with the following feeding reward levels: 0.6 g trigger self-feed

. y1 _Ž _. y1 _Ž

low, SFL , 1.0 g trigger self-feed medium, SFM , and 1.7 g trigger self-feed high, .

SFH . Time and date of each impulse from the rods was read online by a PC computer Ž

and stored on disk. Fish were weighed individually every 4 weeks called periods

. Ž .

hereafter in a 12-week trial 24 July–16 October 1997 after one day of feed

Ž .

deprivation. Abiotic parameters temperature, dissolved oxygen and salinity were recorded daily. There was no collection or measurement of uneaten feed and faeces. Direct observation of feed wastage in tanks was made twice a day and existence of uneaten feed was noted. Dead fish were counted and weighed on a daily basis.

Ž Ž y1_. _Ž _.

Specific growth rate SGR % day s100= ln final biomassyln initial biomass

y1_. _Ž _{Ž .} _.

=no. of days , biomass gain Gain g sfinal biomassyinitial biomass , feed

Ž y1_.

efficiency ratio FERsGain=feed supply , the coefficient of body weight variation Ž_CV_s₁₀₀₌_{standard deviation}₌_meany1_. _{and total survival Survival}_Ž _s₁₀₀₌_Ž_final

. y1_.

no. of fishyinitial no. of fish =initial no. of fish were calculated per tank. In order to estimate N and P loss, a pool of 20 sea bass at the beginning of the experiment and 15 sea bass per tank at the end were killed by an overdose of ethylene glycol-monophenyl ether and stored at y208C for balance studies. Chemical analyses on whole fish and feed were carried out on deep-frozen homogenates according to standard methods: dry

Ž .

matter after drying at 1048C during 24 h, nitrogen N content by Kjeldahl method after Ž .

acid hydrolysis and phosphorus P by spectrophotometric analysis of the phospho-Ž

vanadomolybdate complex after mineralization and acid digestion ISOrDIS 6491 .

method . N and P loss were deducted from N and P supply and gain:

Nutrient loss g

Ž

=kg fish gainy1

.

s1000=

Ž

Nutrient supplyyNutrient gain

.

=Gainy1, with

Nutrient supply g

Ž .

sFeed supply=Feed nutrient content; and

Nutrient gain g

Ž .

s

Ž

Bf=final carcass nutrient content

.

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()

M.

Paspatis

et

al.

r

Aquaculture

184

2000

77

–

88

80

Table 1

Ž . Ž . Ž .

Mean values "S.D., ns3 of initial and final mean individual weight BW and BW , final coefficient of variation of individual weight CV , survival, SGR,i f f

biomass gain, total feed supply and FER in groups of European sea bass subjected to different feeding practices. See text for details of feeding practices Feeding practice

AF100% AF50% AF50%M SFL SFM SFH

Ž .

BW gi 3.45"0.05 3.48"0.09 3.43"0.05 3.50"0.07 3.39"0.02 3.50"0.05

U

Ž .

BW gf 19.16"1.69 cd 14.38"0.67 bc 14.26"1.49 b 24.09"1.12 a 20.03"1.33 ad 20.53"2.31 ad

Ž .

CV %f 25.17"2.52 20.48"3.61 20.18"3.07 26.46"1.45 27.21"0.99 26.93"3.68

Ž .

Survival % 98"2 96"2 97"1 99"1 97"1 99"1

y1

Ž .

SGR % day 2.04"0.11 ab 1.69"0.07 b 1.69"0.15 b 2.30"0.07 a 2.11"0.08 a 2.09"0.17 a

Ž .

Gain g 779.44"78.35 c 535.09"28.14 b 532.27"75.31 b 1029.60"57.31a 824.19"66.75 ac 846.03"113.83 ac

Ž .

Feed supply g 1353"60 bc 576"10 c 557"47 c 1755"204 bc 2547"993 b 2812"1234 b FER 0.57"0.04 b 0.93"0.03 ae 0.95"0.06 a 0.60"0.11 bde 0.37"0.17 bcd 0.21"0.14 c

U

Ž .

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Data analysis was performed with STATISTICA software and included: control for

Ž .

normality of raw data by the Kolmogorov–Smirnov test, analysis of variance ANOVA between feeding protocols, followed by the Scheffe F-test for comparisons between

´

Ž . Ž .

significantly different means P-0.05 , and principal component analysis PCA for Ž .

classification as follows: 1 Frequency distribution of fish body weight between feeding methods: six distributions of fish populations from the respective feeding methods were grouped and compared to the initial fish population; all of them were divided into 10

Ž .

equal weight ranges and data were expressed in percentage. 2 Daily feeding patterns resulting from the three self-feeding regimes in two time periods: 10 days at the

Ž . Ž .

beginning SFL , SFM , SFHi i i and 10 days at the end of this trial SFL , SFM , SFH .f f f

3. Results

Feeding protocol did not affect the survival of sea bass, which was high in all groups Ž_{Table 1 . The few dead fish did not have any external symptoms caused by disease or}. cannibalism and their death was not related to their body weight nor did it coincide with any particular environmental event.

3.1. Growth and feed efficiency

Growth was significantly affected by feeding protocol. Indeed, final mean body

Ž . Ž

weight BW was higher in self-fed groups than in AF50% and AF50%M groups Table_f

Fig. 1. Change in SGR over the feeding experiment with European sea bass. Vertical bars indicate one

Ž .

standard deviation ns3 . Columns within each period with different letter are significantly different

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Fig. 2. Frequency distributions of initial and final body weight of European sea bass subjected to different feeding practices. See text for details of feeding practices.

.

1 ; the highest BW was achieved in the SFL group, with significantly higher valuesf

than in all the automatic feeding groups. This trend for the highest growth in fish fed

Ž .

using self-feeders with a low reward level SFL group was accompanied by a higher Ž

SGR and Gain compared to the other feeding protocols including SFM and SFH

Table 2

Ž .

Mean values "S.D., ns3 of N and P supply, gain and loss in groups of European sea bass subjected to different feeding practices. See text for details of feeding practices

Feeding practice

AF100% AF50% AF50%M SFL SFM SFH

U

Ž .

N supply g 97.5"4.3 bc 41.5"0.7 c 40.1"3.4 c 126.5"14.7 bc 183.7"71.6 b 202.8"8.0 b

Ž .

P supply g 14.9"0.6 bc 6.3"0.1 c 6.1"0.5 c 19.3"2.2 bc 28.1"10.9 b 31.0"13.6 b

Ž .

N gain g 20.7"2.0 c 14.0"0.7 b 14.6"2.0 b 26.5"2.2 a 21.4"1.9 ac 22.1"2.7 ac

Ž .

P gain g 5.7"0.6 c 3.9"0.2 b 4.1"0.3 b 7.0"0.5 a 5.5"0.6 ac 6.3"0.8 ac N loss 101.4"9.3 ab 54.4"4.5 b 50.0"6.2 b 99.1"22.5 a 202.3"93.1 a 210.8"85.3 ab

y1 Žg=kg fish gain .

P loss 12.2"1.0 ab 5.0"0.8 b 3.9"0.4 b 12.2"3.4 a 28.2"14.2 a 28.7"12.9 ab

y1 Žg=kg fish gain .

U

Ž .

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.

groups . A significantly higher growth rate was measured in self-fed fish in period 1 while in the remaining periods, fluctuation of SGR between feeding conditions was

Ž .

similar Fig. 1 .

The total feed supplied was much higher in SFM and SFH groups than in the other

Ž .

groups Table 1 , while in the SFL group, the feed supplied was similar to the AF100% group. FER was negatively related to feed supply, with the highest values in AF50% and AF50%M groups. In the course of the trial, uneaten feed was only observed in AF100%, SFH and SFM tanks.

Ž .

The initial coefficient of variation in body weight CV was 19%. CV was between_i _f 20% and 27% at the end of the experiment, but was not affected by feeding protocol ŽTable 1 . However, PCA of frequency distributions in initial and final individual weight.

Ž .

revealed significant differences in relation to the feeding practice Fig. 2 . The classifica-tion explained 81% of the total variance, and pooled the groups into three clusters: the first one referred to the initial population and the SFL group with a high proportion of big fish, the second pooled the AF50% and AF50%M group with a high percentage of

Ž .

Fig. 3. Histogram representation of the total number of feed demands open bars and the total feed supply

Žtilled bars in relation to feed reward level in self-feeding treatments with European sea bass. Vertical bars.

Ž .

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small fish, and the third pooled AF100%, SFM and SFH where fish had intermediate features.

3.2. N and P gain and loss

The effect of feeding protocol on N and P gain is shown in Table 2. Because feed refusals could not be measured in this experiment, N and P retention are not presented.

Ž .

N and P loss were affected by feeding treatment in the opposite way to FER Table 1 ,

Ž .

but were not related to nutrient gain Table 2 . The highest losses were observed in SFM and SFH groups where, as mentioned above, part of the demanded feed was uneaten. Although N and P gain was higher in the SFL treatment than in the AF100% treatment, loss was identical in these groups. This result indicates the advantages of using on-demand feeding systems for juvenile sea bass. However, groups of fish fed half the recommended level of feed had much lower N and P loss than fish subjected to the other feeding treatments, indicating that the demand protocol used can probably be optimised.

3.3. Demand feeding actiÕity and rhythm

In fish fed using self-feeders, there was a trend for a decrease in demand feeding activity when the reward level increased, but this behavioural compensation was not

Ž .

effective enough to accurately regulate the feed supply Fig. 3 . The feed supply was

Ž .

affected by the reward level Fig. 3 . Two main factors of PCA, covering 85% of the

Ž .

Fig. 4. Daily feeding patterns of European sea bass when self-fed at three reward levels ns10 . SFL, SFM,

Ž . Ž .

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total data variance, grouped the daily feeding patterns of self-fed fish into the following categories: a pattern of restricted daylight activity and a dusk peak at 2000 h was

Ž .

observed in all groups at the beginning of the trial SFL , SFM , SFH ; a pattern with ai i i

Ž .

diurnal peak at 0600–1100 h and a secondary nocturnal peak at 1900 h SFL , SFM ,f f

and a pattern with a continuous increased diurnal activity and a secondary nocturnal

Ž . Ž .

peak at 1900 h SFH_f Fig. 4 . Regardless of the self-feeding regime, fish had a stable low-demand feeding activity with a peak around dusk at the beginning of the trial. In

Ž

contrast, they had increased their activity in specific hours of the day mainly morning .

and early night hours by the end of the trial.

4. Discussion

The different feeding protocols tested did not have any noticeable effect on fish survival. Although feed supply was restricted in two out of the six groups, no cannibalistic phenomena appeared. Conversely, a strong effect of feeding practices on growth was observed. In self-fed fish, it was remarkable that the level of feed reward was not positively correlated with fish growth. The high amount of uneaten feed found in high reward levels caused water turbidity and resulted in bad rearing conditions.

Ž y1 y1 _.

Reward level in SFL protocol 0.6 g feed trigger equals 3.5 g feed kg fish was appropriate for sea bass growth, although it was much higher than the proposed

Ž . Ž

optimum reward in small groups of rainbow trout Oncorhynchus mykiss between 0.1

y1 _.

and 0.5 g feed kg fish, Alanara, 1994; Gelineau et al., 1998 . According to our

¨ ¨

´

personal observations, when sea bass demand fed, they triggered self-feeders, caught some sinking pellets and the rest was abandoned on the bottom of the tanks. Conse-quently, sea bass fed with high reward did not reduce their feeding demand proportion-ally with the reward level. But this situation is not always the rule. Arctic charr

Ž_SalÕelinus alpinus limited and increased their bite activity in low and high reward,.

Ž

respectively, and rainbow trout also regulated their activity quite well Brannas and

¨

.

Alanara, 1994; Gelineau et al., 1998 . In view of these results, additional experiments

¨ ¨

´

with sea bass using self-feeders with lower reward levels than in the present experiment are needed.

In the group fed with automatic feeders according to the feed manufacturer’s recommendations, fish were apparently fed near satiation but their growth was lower than in SFL group. Their total feed supply was similar, but some waste of feed was

Ž .

observed during the course of the experiment. Similarly, Azzaydi et al. 1998 found that sea bass grew faster when they have access to a self-feeder than when they are fed an identical amount of feed supplied by automatic feeders. In AF50% and AF50%M groups, mean individual final weight was only two-thirds of the other fish groups. No difference in any parameter could be found between the fish fed throughout the whole day and those fed in two meals per day, and their final population structure was more

Ž .

homogenous than in all the other groups. Fontaine et al. 1997 , working on Eurasian

Ž .

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Ž .

what was indicated for Salmonidae by Ryer and Olla 1996 , but consistent with the

Ž .

results presented by Gelineau et al. 1998 . An overview of fish population development

´

throughout the experiment showed that only SFL fish had a frequency distribution similar to the initial total population. This finding shows the influence of feeding methods on changes in fish weight distribution with the passage of time. Furthermore,

Ž .

our results, like those of Azzaydi et al. 1998 , demonstrate that the use of self-feeders with a high reward level do not necessarily lead to an increase in growth heterogeneity. FER was high in the group fed half the recommended ration with automatic feeders,

Ž .

reaching up to 0.93–0.95. In the work of Xie et al. 1997 on Nile tilapia, Oreochromis

niloticus, the optimum ration for maximum feed efficiency was also lower than the

satiation level. In both cases, however, because real feed intake was not accurately measured, it was difficult to determine if this was due to the fact that fish fed the recommended ration were wasting part of the feed supply or if feed efficiency was

Ž .

affected by feed intake Azevedo et al., 1998 . The FER obtained in the AF100% and SFL groups was intermediate compared to the other groups, but, from a practical point of view, SFL treatment better coincided with farmer demands: higher growth with similar feed supply. Considering that feed composition is not homogeneous in various studies, it is difficult to compare the different FERs obtained in our study with the results presented by other authors. Nevertheless, FER is always found to be well below

Ž

1, as in our study Hidalgo et al., 1987; Tibaldi et al., 1991; Tsevis et al., 1992; .

Ballestrazzi et al., 1994; Garcia-Alcazar et al., 1994; Lemarie et al., 1998 .

´

If the results from SFM and SFH are set apart because there was obviously a large amount of feed waste, then N and P loss observed in our trial was well within the range

Ž

of published data Handy and Poxton, 1993; Ballestrazzi et al., 1994; Dosdat et al., .

1996; Diaz et al., 1998; Kaushik, 1998; Lemarie et al., 1998 . The lowest loss values

´

were observed when fish were fed a restricted amount of feed, a situation that was not in favour of good growth. The best compromise in terms of loss and growth was found in the SFL group, indicating that self-feeders are well adapted for sea bass provided the reward level was set correctly in order to avoid uneaten food.

The daily feeding patterns of self-fed fish groups were independent of reward level. It could be hypothesised that the high reward would result in fish restricting their hourly feed demands, but it did not. In contrast, all fish groups followed a common daily feeding profile which shifted from dusk and nocturnal to mainly diurnal with a secondary peak early at night. This flexibility in the feeding rhythm of sea bass could explain why some discrepancies existed between results from different laboratories Ž_{Anthouard et al., 1993; Begout-Anras, 1995; Sanchez-Vazquez et al., 1995a,b; Boujard}

_´

. et al., 1996 .

Acknowledgements

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