Impacts of Bacillus sp. probiotics on the growth and serum biochemical indices of rainbow trout larvae in different stocking densities

In the present study, the effects of dietary supplemented feed with a mixture of probiotic Bacillus sp. (1 × 108 CFU/100 g) were investigated on the growth performance and serum biochemical indices of Oncorhynchus mykiss larvae (0.23 ± 0.08 g) in different stocking densities. The experiment was conducted to a completely randomized design with four treatments and a control group with three replicates. The treatments based on the levels of stocking densities were 30, 45, 60 and 75 larvae (T30, T45, T60 and T75) in 10-L tanks. The stocking density of control group was 30 fish per 10-L tank (C10). The feeding period was 45 days. The highest final weight (3.06 ± 1.16 g) and the lowest FCR (1.01 ± 0.39) were observed in T60 (p<0.05). The SGR was significantly reduced in all experimental treatments compared to the control group (p<0.05). The highest total protein (9.70 ± 2.10 mg dL-1) and cortisol (84.50 ± 2.50 mg dL-1), and the lowest albumin (9.85 ± 1.05 mg dL-1) was measured in T30 (p<0.05). The highest glucose level (139.50 ± 4.50 mg dL-1) was measured in T60 (p<0.05). Adding probiotics to the diet of rainbow troutlarvae led to significantly reduced AST as well as increased ALT and ALP activities in the experimental treatments compared to control group (p<0.05). In conclusion, the results of this study showed that Bacilliprobiotics are capable of enhancing growth rate and also serum biochemical indices in rainbow troutlarvae. These findings may support the potential application of this probiotic as a practical supplementation in the diet of fish.