Effects of Potential Probiotic Enterococcus casseliflavus (EC-001) on Growth Performance, Immunity, and Resistance to Aeromonas hydrophila Infection in Common Carp (Cyprinus carpio)

The effects of different levels of dietary Enterococcus casseliflavus (EC-001), as a potential probiotic, were investigated on the growth performance, hemato-biochemical parameters, immune responses, and resistance to Aeromonas hydrophila infection in common carp (Cyprinus carpio) fingerlings. Accordingly, fish (N = 720; 12.0 +/- 0.5 g) were distributed into four treatments receiving different dietary levels of E. casseliflavus, EC-001 (0 [control], 1 x 10(7), 10(8), and 10(9) CFU g(-1) feed), for 8 weeks. The fish fed with a diet containing 10(9) CFU g(-1) showed the highest weight gain and specific growth rate, along with the lowest feed conversion ratio, compared with the control group (P < 0.05). Red and white blood cells, hemoglobin, hematocrit, neutrophils, and monocytes significantly increased in the fish fed with 1 x 10(8) and 10(9) CFU g(-1) (P < 0.05). Dietary inclusion of 1 x 10(8) and 10(9) CFU g(-1) significantly increased serum total protein, albumin, and immunoglobulin content (P < 0.05). Feeding the fish with 1 x 10(9) CFU g(-1) resulted in a significant increase in serum and skin mucus lysozyme activity compared with the other groups (P < 0.05). Complement component 3 and skin mucus protease activity were also significantly higher in all the fish treated with dietary E. casseliflavus (EC-001) compared with the control group (P < 0.05). The cumulative mortality in the treated fish was lower (ranging from 10 to 22%) than the control group (31%) after challenging the fish with A. hydrophila infection, while the fish fed with E. casseliflavus (EC-001) at 1 x 10(9) CFU g(-1) exhibited the lowest mortality rate (P < 0.05). In conclusion, our results revealed the potential probiotic effects of E. casseliflavus (EC-001) for enhancing growth performance, immunity, and disease resistance of common carp.