Effect of Bacillus subtilis on gonadal development, growth and body composition in zebrafish (Danio rerio)

This study assessed the probiotic effects of dietary supplementation with Bacillus subtilis HBB 493® on growth, survival, gametogenesis, and intestinal health of zebrafish (Danio rerio). 600 juveniles were divided into five experimental groups namely: Control group I (0.0 cfu/g), group II (6.5x109 k/g), group III (1.3x1010 cfu/g), group IV (2.6x1010 cfu/g) and group V (3.9x1010 cfu/g). Each treatment and control had three replicates, while each replicate had 40 fish. The duration of the experiment was 100 days. At the termination of the experiment, gonads, and intestine were histologically assessed. Protease activity value of feeds and economic analysis of diet supplemented with B. subtilis was calculated. Growth parameters, in the fish fed 3.9x1010 cfu/g were significantly different from those observed in the control, group II, and group III B. subtilis fed groups (P<0.05), and group V was the best. There were no significant differences in the survival rate between treatment groups including control (P>0.05). The histological observations of the gonads reveal differences among the fish fed different levels of B. subtilis. Fish fed diets II, III, IV and V had more developed gonads compared to those on diets without B. subtilis. The status of villus and goblet cells was used to assess the intestinal health of the fish fed diets supplemented with B. subtilis. Villus and goblet cells were intact in all the different levels of B. subtilis supplemented groups. The highest protease activity value was measured as 75.47±3.18 U/mg protein in the fish fed highest level of B. subtilis. These findings support the growth parameters and histological results. Economic conversion rate was lowest in the fish fed 3.9x1010 cfu/g group. Whereas, economic profitability index was highest in the same group, suggesting profitability of diets supplemented with B. subtilis in Zebrafish. Taken all together, the present study suggested that the dietary supplementation of 3.9x1010 cfu/g probiotic B. subtilis should be used for the enhancement of growth parameters, survival rate, gametogenesis and intestinal health in ornamental zebrafish.