Isolation of protective probiotics for tilapia (Oreochromis niloticus, Linnaeus 1758): Investigation of growth performance and protection against Streptococcus iniae

In the present study, the effects of two bacillus strains (Bacillus subtilis and Bacillus mojavensis), isolated from intestinal mucus of Tilapia (Oreochromis niloticus), on growth performance, intestinal morphology, innate immunity and disease resistance of fish were evaluated. A total of 375 indivual fish were divided into five groups in triplicate. Nile tilapia were fed a basal diet and probiotics at different concentrations of 1×106 (BM6;BS6) and 1×108 (BM8;BS8)(CFU/g) of feed for 60 days. After feding trial, probiotic-fed Tilapia showed significantly better growth performance than control group. Light microscopy observations revealed elevated goblet cells and intestinal villi length and perimeter ratio increase in the intestine of probiotic fed tilapia compared with control. Electron microscopy revealed an increase in microvilli length and density in probiotic fed tilapia compared with control. Additionally, probiotic-fed Tilapia showed significantly increased expression of cytokine genes in the intestine and protection against Streptococcus iniae compared to the control group. These data suggest that candidate probiotics used in the present study have positive effects on the growth performance, gut morphology and disease resistance of Tilapia.