Formation of brood fish shoals from farmed breeders (Phase 1: Biotechnique of Beluga (H. huso) Rearing in Freshwater)

anglais. The present study was conducted to determine ideal diets for the commercial culture of beluga under rearing conditions. The objective of this study was to determine optimum protein levels in adaptation, growth and maintenance diets used in the four study phases. In the first phase 2400 beluga larvae with an average weight of 400-700 mg were stocked at a density of 200 larvae m -2 . Four treatments were used and four replicates run for each treatment. On the basis of results obtained, larvae in &lsquoTreatment A&rsquoshowed highest growth (P0.05). In the second phase, beluga specimens with an initial weight of 4.3 ± 0.14 g were studied for a period of 139 days in a random block design and were fed three different experimental diets at a rate of 2-3 % of their body weight. Three replicates were used for each treatment. Percentage body weight increase (% BWI), FCR, SGR and growth rates were significantly influenced by the protein content of the diets used (P0.05). On the basis of Analysis of variance and Tukey Test conducted on results obtained the protein requirement for beluga in the 5-50 g weight class is about 50 %, and with an increase in body weight to about 120 g the protein requirement decreases to 45 %. Therefore diets can be formulated from good quality protein sources 45-50 % crude protein to achieve maximum growth in juvenile hatchery reared beluga. In the third phase 130 day old beluga specimens with an average body weight of 95 ± 1.2 g were reared for a period of 110 days on five experimental diets (three replicates run for each treatment) containing 40-50 % protein and similar levels of fat and energy. In the forth phase 240 day old specimens with an average body weight of 453.3 ± 8.3 g were reared on three experimental diets (ideal diets determined from first phase) (three replicates run for each treatment) for a period of 120 days. Diets were fed four times a day at 1.5 – 2 % of body weight. It is evident from the comparison of mean values in different treatments studied that different levels of protein produce varying effects on growth rates in beluga specimens. Significant increase in body weight, SGR value and final body weight was observed in beluga specimens that were fed on diets containing high protein from suitable protein sources (P0.05). FCR values also improved in diets containing high protein but was not (P0.05). On the basis of maximum % BWI, growth and minimum FCR values it is evident that the maximum crude protein requirement in beluga sturgeon in the weight range of 90 – 550 g that produces good growth and has no adverse effect on body composition is about 45 ± 2 % from a suitable protein source. Although fishes fed diets containing 50 ± 1 % crude protein showed better growth rates as compared to those fed diets containing 45 % protein, no significant differences were observed. It was also evident that protein requirement for beluga sturgeon in the 500-1000 g body weight range is 40 ± 2 g from a suitable protein source. Beluga sturgeons weighing 20.51 ± 0.32 to 1068.23 ± 26.35 g were studied in three study phases for a period of 335 days in fiberglass tanks (500 L) in order to determine the ideal number of feeds. Water flow into the tanks was maintained at 0.15 L sec -1 and fishes were fed 3, 5 and 8 times per day. Three treatments were used in each study phase and three replicates were run for each treatment. On the basis of results obtained from the first phase (mean weight 20.51 ± 0.32 g) increase in number of feeds resulted in higher growth rates, % BWI, SGR and lower FCR values however no significant differences were observed in the three groups under study (P0.05). In the second phase (mean weight 77.55 ± 1.18 g) on the basis of the variations in weight in the first and final biometric measurements it was clear that Treatment C (8 times feeding per day) was different from other treatments (P0.05).

anglais. However no significant differences were observed among the treatments studied regarding FCR, SGR etc. (P0.05). No significant differences were observed among the treatments in length and weight measurements carried out in the third phase (mean weight 257.61 ± 6.08 g) (P0.05). On the basis of SGR, FCR and % BWI values and growth rates observed during the rearing period it can be concluded that increase in number of feeds given per day has no significant effect on the parameters studied. Fish can adapt itself to the feeding times and intervals, however since feeding is carried out manually in Iran, best results for growth are achieved when feeds are given 8 times during the day in the early stages (30-50 g) and 3-5 times, preferably 4 times, for 50-70 to 1000 g weight classes. The effect of stocking density on growth rate, FCR and survival rate was studied in three study phases in order to determine ideal stocking densities for hatchery reared beluga in the 49.44 ± 1.52 to 2158.88 ± 26.82 g weight class. The study was conducted for a period of 270 days in 2000 L fiberglass tanks under similar conditions of rearing. Water exchange was carried out at a rate of 15-20 % per hour. In the first phase two stocking densities (300 and 500 specimens /m 2 ) with a mean weight of 49.44 ± 1.52 g were considered. This phase lasted 65 days. In the second phase, 3 stocking densities (1.6, 2.8 and 4 kg/m 2 ) were considered. The mean weight of fishes was 92.09 ± 1.72 g and this phase lasted 100 days. Four stocking densities (1.5, 2.5, 3.5 and 4.5 kg/m 2 ) were considered in the third phase. This phase lasted 120 days and the mean weight of fish was 918.13 ± 21.87 g. The results obtained indicate adverse effects of increase in stocking density on % BWI, SGR and FCR values. Fishes stocked at higher density in phase one showed body wounds and deformed fins as a result of crowding. Significant differences (P0.05) were observed in growth rates recorded for fishes stocked at lower densities (1.6 kg/m 2 ) in phase two as compared to those recorded for fishes stocked at 2.8 and 4 kg/m 2 . In the third phase of rearing growth rates in fishes decreased with an increase in stocking density. Fishes stocked at 1.5 kg/m 2 showed 7.2, 15.6 and 19.8 % higher growth rates as compared to fishes stocked at 2.5, 3.5 and 4.5 kg/m 2 , respectively (P0.05). Statistical analysis of results obtained from the present study indicate that increase in stocking density per unit surface area causes a decrease in feeding surface area for each individual fish (considering the bottom feeding behavior in beluga) and thus results in different weight classes, feeding interaction among fishes and ultimately leads to unequal shares in food intake, increases fluctuations in length and weight and lowers the advantages of feeds. On the basis of the results obtained ideal stocking density in the early stages of rearing beluga up to a weight of 50-10 g can be stated as 1.5 to 2 kg/m 2 and 2.5 to 3 kg/m 2 for rearing above 900 g. Growth in A. persicus and beluga from the larval stage up to one-year class was studied under similar conditions of rearing in fiberglass tanks for a period of 411 days. Three replicates were run for each treatment. Fishes were fed granule feeds containing 40 % protein and 13 % fat. The mean weight of A. persicus increased from 16.6 ± 0.51 g to 417.15 ± 26.5 g and that of beluga increased from 41.59 ± 0.83 to 928.47 ± 46.9 g at the end of the rearing period. Moreover despite cannibalism observed in beluga in the larval stage, this species adapted easily to formulated diets and showed suitable survival rates. Results obtained from growth rates (weight and length) and other parameters such as FCR, SGR and % BWI that were calculated from growth rates indicate that beluga exhibits significant growth rates as compared to A. persicus under similar conditions of rearing (55.1 % higher growth rates as compared to those in A. persicus). On the basis of the results obtained from a 29 weeks study period carried out on the commercial culture of beluga with a mean weight of 33.75 ± 0.35 g in fiberglass tanks and earthen ponds. At the end of the study period of 200 days, beluga specimens reared in fiberglass tanks showed an increase in weight of 572 g and a production 6 kg m -2 . The percentage survival, FCR and SGR values recorded for this group were 98.4 %, 2.21 and 1.41, respectively. The weight increase and production for beluga specimens reared in earthen ponds during the same study period were 708 g and 1.5 kg m -2 , respectively. The percentage survival, FCR and SGR recorded for this group were 85.7 %, 1.32 and 1.69, respectively. No significant differences (P0.05) were observed in the different parameters recorded in the two groups studied, however SGR and FCR values obtained for beluga specimens reared in earthen ponds were more suitable. Growth rate on the other hand was significantly influenced by the rearing system (P0.05). Data obtained indicate that the mean weight of beluga specimens reared through a period of 17 months in fiberglass tanks (2 x 2 x 0.53 m) increased from 0.2 g to 3753 ± 72.2 g. The percentage survival was 90 % and FCR and SGR recorded for this period were 2.02 and 1.01 ± 0.15, respectively. Therefore it can be concluded that beluga can be reared in aquaculture systems under the climatic conditions in Gilan. Water exchange for rearing tanks should be carried out 4-5 times per day and at a rate of 10-12 % per day in earthen tanks. From the economic point of view the net profit obtained from fiberglass tanks is 8000-10000 Rials per kilogram sturgeon meat. Application of aeration, suitable water quality and use of low quality fish in diets in order to lower costs leads to higher productions per unit area and thus results in higher profits. Key words: Beluga, A. persicus, commercial culture, fiberglass tanks, stocking density, feeding times, FCR and SGR