Effects of adding two native bacterial strains (Lactococcus lactis and Weissella confusa) on growth performance, immune indices, and intestinal flora of juvenile great sturgeon (Huso huso)

This study was carried out to determine effects of diets supplemented with two bacterial strains (Lactococcus lactis and Weissella confusa) on the growth performance, immune indices and intestinal microflora of great sturgeon juveniles. At the beginning of the feeding trial, the mean weight ( ±SD) of the fish was 79.44 ±3.18 g. At random, 15 fish were stocked per each fiberglass tank (1m ×1m ×0.5m) containing 300 L freshwater. The diets were prepared through spraying 50 ml bacterial suspensions containing 150, 300, and 450 mg of the bacterial strains per kg of pelleted diets to make certain concentrations 1.5 ×10^9 cfu/g (T_1), 3 ×10^9 cfu/g (T_2), 4.5 ×10^9 cfu/g (T_3). The blood neutrophils in the T_1 and T_2 significantly increased as compared to the control group and T_3. Lymphocytes in the control and T_3 were significantly more than T_1 and T_2. However, eosinophils showed no change between the fish fed with the supplemented diets and control group. Monocytes in T_3 considerably decreased when compared to T_1, T_2, and control. IgM and C_3 in the experimental treatments were significantly higher than the control. Lysozyme, C_4, and ACH50 in T_1 an T_2 were significantly higher than T_3 and control. Colony count of lactic acid bacteria in the intestine of fish in T_1 and T_2 was significantly higher than the control and T_3 groups. Colony count of the aerobic and facultative anaerobic bacteria in the intestine of fish in the medium of TSA in control was significantly more than T_1 and T_2. Since the TSA medium is a kind of nonselective environment and provides sufficient nutrients for a wide range of microorganisms, the medium indicated that intestinal microflora condition was worse in the control fish. The growth performance indices (weight gain, biomass increase, specific growth rate, daily weight gain, and condition factor) demonstrated no significant difference between treatments and control. There was no significant difference in term of FCR between control, T_1, and T_3. Overall, it can be stated that the two bacterial strains could induce favorable influence on intestinal microflora, immune indices, biochemical parameters, and growth performance at two levels of 150 mg (T_1) and 300 mg (T_2) especially in the T_2.