Effects of single and multi-strain probiotics on the growth, hemato-immunological, enzymatic activity, gut morphology and disease resistance in Rohu, Labeo rohita

The present study was aimed at evaluating the effects of Bacillus strains obtained from the mangrove environment as dietary probiotic on Rohu, Labeo rohita. Under the laboratory trial, Rohu fingerlings (average weight 5.02 +/- 0.85 g) were fed with nine experimental diets containing B. amyloliquefaciens BN06 (106 cfu/ g feed as Treatment 1 (T1) and 109 cfu/ g feed as T2), B. subtilis WN07 (106 cfu/ g feed as T3 and 109 cfu/ g feed as T4), B. megaterium CT03 (106 cfu/ g feed as T5 and 109 cfu/ g feed as T6) and a mixture of all the three bacteria in equal parts (106 cfu/ g feed as T7 and 109 cfu/ g feed as T8) and control feed (C) without probiotic bacteria for 45 days. After 45 days of feeding trial, the fishes were challenged with Aeromonas hydrophila, and survival percentage was recorded for 10 days. Results revealed that weight gain and specific growth rate were significantly higher (P < 0.05) in T7 and T8 than control. Hemato-immunological parameters such as white blood cells, red blood cells, hemoglobin, and serum superoxide dismutase activity were significantly higher in T7 than control. Intestinal alpha-amylase and protease activities were considerably higher in T7 than control and all other treatments. Significantly higher villi length and post-challenge survival was observed in T7 than control. A field trial was conducted in earthen ponds for four months to revalidate the obtained results. Carp fingerlings comprising of rohu (average weight 9.92 +/- 1.25 g) and catla (average weight 3.12 +/- 0.43 g) were distributed in three treatment groups containing the formulated feed with a mixture of B. amyloliquefaciens BN06, B. subtilis WN07 and B. megaterium CT03 at 106 cfu/ g feed as FT1, formulated feed without probiotic bacteria as FT2 and farmer's practice comprising of a mixture of rice bran and groundnut oil cake as FT3. At the end of field trial, the results showed that growth and hemato-immunological parameters were significantly higher (P < 0.05) in FT1 than FT2 and FT3. The present study revealed that multi-strain probiotics comprising of B. amyloliquefaciens BN06, B. subtilis WN07 and B. megaterium CT03 at 106 cfu/ g feed could be a more effective source of dietary probiotic for rohu fingerlings, which further proved that the bacteria isolated from mangrove environment could confer beneficial effects to the freshwater fishes.

Automated summary

The study evaluated the effects of Bacillus strains from mangrove environment as dietary probiotics for Rohu fingerlings. Results showed significant improvement in growth and immune parameters with the multi-strain probiotics, supporting the beneficial effects of mangrove bacteria on freshwater fishes.