Effects of single or conjoint administration of lactic acid bacteria as potential probiotics on the growth, immune responses, and disease resistance of Carassius auratus.

Probiotics have been documented to promote growth, immunity, and disease resistance in farmed fish. In the present study, we aimed to evaluate single or conjoint effects of some lactic acid bacteria (LAB), namely, Lactococcus lactis, Lactobacillus rhamnosus, and Enterococcus faecalis on the growth performance, immune response, and disease resistance of Carassius auratus. Fish were fed a basal diet supplemented with L. lactis (group B), L. rhamnosus (group C), E. faecalis (group D), L. lactis + L. rhamnosus (group E), L. rhamnosus + E. faecalis (group F), L. lactis + E. faecalis (group G), and L. lactis + L. rhamnosus + E. faecalis (group H) at 5.0 × 10⁸ CFU/g diet for 34 days. After feeding, the final body weight (FBW), weight gain (WG), specific growth rate (SGR), and survival had significantly increased (p < 0.05) for group E. The results indicated that single or conjoint administration of LAB induced high levels of IgM, LZM, AKP, and SOD activity in serum, which may effectively induce humoral immunity, and group E induced even higher levels. At the same time, when compared to the basal diet (group A), the results of qPCR showed that probiotic administration significantly upregulated (p < 0.05) the expression of IL-10, IL-1β, TNF-α, and IFN-γ in the spleen, kidney, liver, and intestine of C. auratus. After challenge with the Aeromonas hydrophila, the survival rates in all probiotic-fed groups were significantly higher (p < 0.05) than those of group A, and the relative protection rates of groups B, C, D, E, F, G, and H were 27%, 30.7%, 40.94%, 42.32%, 39.38%, 33.61%, and 37.5%, respectively. Our data indicated that probiotics could promote growth, enhance immune indicators, and enhance immune capacity. In summary, combined administration of probiotics had a better effect on C. auratus. This experiment could provide a reference for the optimal combination of probiotic additives for aquatic animals. [ABSTRACT FROM AUTHOR]