Effect of different dietary-taurine on growth, feeding performance, digestive enzymes and immunity of beluga, Huso huso, under the low water temperature

Beluga is one of the important endangered species in the Caspian Sea and the main farmed species of sturgeon in Iran. Therefore, the idea of ​​using the growth stimulants through the feed under the low water temperature can be useful for improving its growing efficiency. In this study, 120 fish with the mean weight of 440.15 ± 23 g were fed different animal protein-based diets containing zero, 5, 10, and 15 grams of taurine/kg (Considering the amount of taurine in the basic diet, the amount of total taurine in the diets reached to 3.1, 8.3, 13.0, and 18.1 g / kg, respectively), and reared at 10 ± 1 °C for a 56 –day period. The results of growth indicated a significant and positive effect due to presence of taurine in diet comparing the control treatment. In fact, all the three doses were able to improve the feeding and growth of fish, and the highest percentages of weight gain, specific growth rate, and the lowest food conversion ratio were obtained in treatment containing 8.3 g taurine in diet (a treatment that received an additional 5 g / kg taurine). There were significant differences in condition factor, liver and visceral indices among the treatments (p >0.05), and no mortality was observed among the experimental treatments as well. Also, the highest amylase, lipase and protease enzymes activities were measured in 8.3 g taurine treatment. While the concentration of taurine increased in the diet, the carcass lipid and ash percentages decreased and the protein and moisture percentages increased without any significant difference (p >0.05). Different concentrations of taurine had little effect on nonspecific immunity of fish. Whereas, there were not significant differences in the lysozyme enzyme activities, total immunoglobulin and C3 complement (p >0.05). The highest amount of C4 complement was measured in 8.3 g taurine treatment, which was significantly different compared to other treatments (p <0.05). As a conclusion, the diet containing 5 gr/kg taurine could be the optimum growth stimulant diet, and it can improve the growth efficiency of Beluga fish at the low water temperature (10 ± 1 °C). 
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