Dietary Multispecies Probiotic Supplementation Enhances the Immunohematological Responses and Reduces Mortality by Aeromonas hydrophila in Labeo rohita Fingerlings

A study was conducted to determine the immunomodulatory effect of probiotic mixture on the nonspecific immune response and disease resistance of Labeo rohita. Fish were fed with six different test diets with or without probiotics, namely, T1 (basal feed [BF] without probiotics), T2 (BF+Bacillus subtilis [BS]+Lactococcus lactis [LL]), T3 (BF+LL+Saccharomyces cerevisiae [SC]), T4 (BF+BS+SC), T5 (BF+BS+LL+SC), and T6 (BF+heat-killed bacteria of BS+LL+SC). During the prechallenge period, significantly higher (P<0.01) nitroblue tetrazolium assay (NBT), red blood cells (RBC), hemoglobin (Hb), globulin, and albumin content were recorded in the probiotic-supplemented diet group. Feeding all the three probiotics significantly decreased (P<0.01) the serum aspartate aminotransferases (AST), alanine aminotransferases (ALT), acid phosphatase (ACP), and alkaline phosphatase (ALP) activity and increased the myeloperoxidase (MPO) and immunoglobulin M (IgM) value. Significant difference in the NBT, Hb, serum albumin, and MPO was noticed in both prechallenged and postchallenged fish. Lowest survivability was recorded in the nonprobiotic fed group, followed by the group fed with heat-killed probiotics, whereas the highest survivability was noticed in the group fed with all the three probiotics in live form. Thus, a probiotic mixture diet constituting of three probiotics in viable form is found to be optimum to enhance the immunity and postinfection survivability in L. rohita fingerlings.