Biotechnique of rearing Beluga (H.huso) using brackishwater of the Caspian Sea (Different densities and water flow)
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AuthorPourali Foshtomi, Hamidreza
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AbstractThis study was conducted at the Applied Research Station for Sturgeon Culture (Chaboksar site) and was supported by the Iranian Fisheries Research Organization in order to obtain the bio technique for Huso huso culture in brackish water from the Caspian Sea. The effects of stocking density and water flow at the inlet of brackish water was studied for a period of 4 years using 4 weight classes and the results obtained were compared with those obtained from the culture of H. huso in freshwater. Huso huso in four weight classes of 3-20 g, 20-200 g, 325-1000 g and 1000-3000 g were stocked at stocking densities between 350 g to 15 kg m-2. The effect of water flow in rearing tanks was studied in weight classes 30- 2700 g. In the weight class 3-20 g, highest growth was recorded in H. huso stocked at 1000 g m-2 in brackish water which was significantly higher (P<0.5) than that recorded in freshwater suggesting the advantage of rearing H. huso in brackish water at improved density of 1000 g m-2. Results obtained from total length in juvenile H. husoconform to these results. It may therefore be concluded that in the weight class 3-20 g, stocking density of 1000 g m-2 is not a limiting factor on growth in juvenile H. huso. Low specific growth rate (SGR) was reported with a stocking density of 1500 g m-2 in freshwater which was not significantly different from that in brackish water. Hence rearing juvenile H. huso in brackish water at high densities (1500 g m-2) is preferred to rearing in freshwater as H. huso is more capable of adapting to stressful conditions of stocking density in brackish water. Similar trends were observed for percentage body weight increase (BWI%) showing the advantage of using a stocking density of 1000 g m-2 in brackish water. Production in different groups showed variations depending on stocking density biomass. Condition factor was low when H. huso was reared in freshwater at a stocking density of 1500 g m-2. Similarly CVw was low in the experimental group reared at a density of 500 g m-2 in brackish water, while CVtl in the group reared at 1500 g m-2 in brackish water was low. The calculated value for CVw/tl was low with stocking density of 500 g m-2 in brackish water and freshwater. Final body weight and growth indices in the 20-200 g weight class in the experimental group using 1000 g m-2 in brackish water were higher than that in freshwater. Similarly growth indices and final body weight of juvenile H. huso at 2000 and 1500 g m-2 stocking densities were higher than the values obtained with similar stocking densities in freshwater. SGR and growth rate (GR) of H. huso at stocking density of 1500 g m-2 was significantly higher in brackish water than that in freshwater. Comparison of results obtained from weight and total length in weight classes 325-560 g showed that until they reach a weight of 560 g, stocking density of 1.3 kg m-2 in brackish water is preferred to the densities 2.6, 3.9 and 5.2 kg m-2. Comparison of results indicate that in the weight class 325-560 g, better results are obtained when juvenile H. huso are reared in brackish water at densities of 1.3, 2.6 and 3.9 kg m-2 as compared to that obtained from the use similar densities in freshwater. Statistical analysis of SGR indicates that stocking densities up to 2.6 kg m-2 do not limit growth. Also it was also evident from the analyses of SGR and FCR that stocking density of 5.2 kg m-2 is not considered suitable for juvenile H. huso in the weight class 325-560 g. On the basis of results obtained for SGR, GR and FCR it maybe concluded that up to the 760 g weight class, stocking densities of 1.3 and 2.6 kg m-2 were statistically better than other densities studied. Moreover rearing juvenile H. huso at these stocking densities in brackish water also proved better than that in freshwater. In the weight class 650-1000 g, stocking fish at densities of 2.6 -10 kg m-2 in brackish water did not seem to affect final body weight, total length and SGR. At stocking densities 5.1 and 7 kg m-2, GR for juvenile H. huso in brackish water were significantly higher than that obtained in freshwater using the same stocking densities. Similarly FCR and FE values obtained for juvenile H. huso in this weight class in brackish water were significantly better (P<0.05) than those obtained in freshwater. SGR values obtained at stocking densities 7 and 10 kg m-2 support these findings. Based on body weight, total length and GR values it may be concluded that stocking density of 10 kg m-2 does not restrict growth in juvenile H. huso until they reach a body weight of 1000 g. Similarly a stocking density of 7.5 kg m-2 does not limit growth in juvenile H. huso until they reached a body weight of 1150 g and stocking densities of 5.1 kg m-2 and 2.6 kg m-2 do not limit growth in juvenile H. huso until they reach body weights of 1300 and 1500 g, respectively. Rearing H. huso in these weight classes at different stocking densities of 10, 7.5 and 5.1 kg m-2 in brackish water was significantly better than rearing them in freshwater. Also based on feeding indices (FCR, FE, SGR and GR) in these weight classes, stocking densities of 2.6 and 5.1 kg m-2 in brackish water were significantly more suitable than other stocking densities studied in the same culture medium. Results obtained from rearing juvenile H. huso at stocking densities of 2.6, 5.1 and 7.5 kg m-2 in brackish water was significantly better than that obtained in freshwater at the same stocking densities. Based on growth (SGR, BWI) and feeding (FE) indices in the weight class 900-3000 g it is evident that experimental group 5 (with stocking density of 10 kg m-2 , water flow of 3 L sec-1) was significantly better (P<0.05) than all other groups studied. It may also be concluded from the results obtained by studying stocking densities and water flow that stocking density of 10 kg m-2 used for rearing juvenile H. huso in the weight class 900 g until they reach a weight of 3000 g is not a limiting factor on their growth. It was also observed that juvenile H. huso are highly capable of adapting to their environment. The one-way water supply and daily water exchange with different water flow rates ranging from 1 to 6 L sec-1 yielded similar results. It was clearly evident that a water flow rate of 0.5 L sec-1 in brackish water and freshwater resulted in significantly lower growth in juvenile H. huso. Highest growth was reported in brackish water with a flow rate of 1.5 and 3 L sec-1. In freshwater, highest growth was recorded with flow rates of 3 L sec-1. Higher water flow rates improved growth indices in H. huso. Improved condition factor and variable coefficients of weight and total length were observed in experimental groups in brackish water and freshwater, except in the experimental group with a flow rate of 0.5 L sec-1 in freshwater. In the weight class 530-2000 g, water flow rate of 3 L sec-1 produced higher final weight in juvenile H. huso in freshwater as compared to that in brackish water. Similar results were obtained in freshwater and brackish waterwith water flow rate of 1.5 L sec-1. Data on carcass composition of farmed H. huso indicated no significant effect of freshwater and brackish wateron protein and lipid levels. In both rearing media, diets were formulated to meet the dietary requirements of H.huso and hence carcass composition conformed to the quality of diets.
Publisher or UniversityIranian Fisheries Science Research Institute
Series : Nr89.1484;