Enhancement of growth, innate immunity, and disease resistance by probiotic Enterococcus faecium MC-5 against Aeromonas hydrophila in Indian major carp Cirrhinus mrigala.

E. faecium MC-5 was isolated and characterized from the gut content of C. carpio and supplemented with a pellet diet at the ratio of 1.0 × 10, 1.0 × 10, and 1.0 × 10 cfu g. Then it was fed to Cirrhinus mrigala for 42 days and the growth performances were evaluated. The growth performance of experimental groups was significantly (P < 0.05) increased than the control group. During 21 and 42 days of the feeding experiment, all the tested immunological parameters such as phagocytic, respiratory burst, lysozyme, acid phosphatase (ACP), superoxide dismutase (SOD), myeloperoxidase activities, and IgM level of experimental groups were significantly (P < 0.05) increased than a control group. After 21 and 42 days of feeding experiment, the fishes were challenged with A. hydrophila, and the relative percentage of survival of experimental groups (PT-I to PT-III) over the control group was recorded from 30.94 to 61.53 and 38.04-77.52 %, respectively. During the challenge experiment, A. hydrophila load was enumerated from dead fish at every 7-day interval. The A. hydrophila load in both the tissues of experimental groups decreased positively from the 7th to 14th day of challenge duration. Overall, the results suggested that the addition of E. faecium MC-5 enhanced the growth performance, immunological response, disease resistance to A. hydrophila, and antioxidant defense system in C. mrigala. Hence these results suggest that E. faecium MC-5 could be used as an advantageous probiotic supplement in aquaculture production.