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
Ž .
Cho 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
tank , with ambient water temperature 23.5 0.8
8C and natural light conditions at
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
. Ž
. AF100 every 15 min during daylight; half of the recommended feed AF50 every
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 AF50M . 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
s 100 = ln final biomass y ln initial biomass
y1
. Ž
Ž . .
= no. of days
, biomass gain Gain
g s final biomass y initial biomass , feed Ž
y1
. efficiency ratio FER s Gain = feed supply
, the coefficient of body weight variation Ž
y1
. Ž
Ž CV s 100 = standard deviation = mean
and total survival Survival s 100 = final .
y1
. no. of fish y initial 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 y20
8C 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 104
8C 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 = kg fish gain
y1
s 1000 = Nutrient supply y Nutrient gain
Ž .
Ž .
= Gain
y1
, with
Nutrient supply g s Feed supply = Feed nutrient content;
Ž .
and Nutrient gain g s B = final carcass nutrient content
Ž . Ž
.
f
y B = initial carcass nutrient content .
Ž .
i
M. Paspatis
et al.
r Aquaculture
184 2000
77 –
88 80
Table 1 Ž
. Ž
. Ž
. Mean values S.D., ns 3 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
AF50M SFL
SFM SFH
Ž . BW g
3.450.05 3.480.09
3.430.05 3.500.07
3.390.02 3.500.05
i U
Ž . BW g
19.161.69 cd 14.380.67 bc
14.261.49 b 24.091.12 a
20.031.33 ad 20.532.31 ad
f
Ž . CV
25.172.52 20.483.61
20.183.07 26.461.45
27.210.99 26.933.68
f
Ž . Survival
982 962
971 991
971 991
y1
Ž .
SGR day 2.040.11 ab
1.690.07 b 1.690.15 b
2.300.07 a 2.110.08 a
2.090.17 a Ž .
Gain g 779.4478.35 c
535.0928.14 b 532.2775.31 b
1029.6057.31a 824.1966.75 ac
846.03113.83 ac Ž .
Feed supply g 135360 bc
57610 c 55747 c
1755204 bc 2547993 b
28121234 b FER
0.570.04 b 0.930.03 ae
0.950.06 a 0.600.11 bde
0.370.17 bcd 0.210.14 c
U
Ž .
Data with different letters are significantly different P - 0.05 .
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 , SFH and 10 days at the end of this trial SFL , SFM , SFH .
i i
i f
f f
3. Results
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