Performance evaluation of Nile tilapia (Oreochromis niloticus) fed diets supplemented with Lactobacillus plantarum, Bacillus subtilis and Candida infanticola.

Aquaculture is the fastest-growing agricultural activity globally, providing healthy food with comparatively low environmental impact. However, high stocking densities can generate excessive organic matter, causing stress and increasing pathogen susceptibility in fish. This study evaluated the effects of dietary supplementation with Candida infanticola UFSJ7A, Bacillus subtilis ATCC 19,659, and Lactobacillus plantarum UFSJP2 on Nile tilapia (Oreochromis niloticus) performance, intestinal morphology, in vitro antagonistic activity against fish pathogens, and pond water quality. Supplementation with B. subtilis significantly improved feed conversion ratio, showing results similar to those of L. plantarum and microbial consortium treatments. Dietary supplementation significantly affected feed intake and feed conversion ratio. Fish fed L. plantarum showed the lowest feed intake, whereas the microbial consortium resulted in the highest feed intake. Supplementation with B. subtilis improved feed conversion ratio, with values comparable to those observed for L. plantarum and the microbial consortium. No significant differences were observed in final weight, weight gain, or survival among treatments. No significant effects were observed on fish viability, with survival rates above 90% across treatments. Exploratory intestinal morphometric observations indicated greater microvillus height in fish supplemented with L. plantarum and B. subtilis, suggesting increased nutrient absorption capacity. In vitro antagonism assays demonstrated that only B. subtilis inhibited the growth of (A) hydrophila, whereas L. plantarum and C. infanticola exhibited no antagonistic activity against the tested pathogens. None of the dietary treatments negatively affected water quality, which remained within suitable ranges throughout the experimental period. Overall, dietary supplementation with (B) subtilis improved feed utilization, whereas B. subtilis and L. plantarum were associated with exploratory changes in intestinal morphology. Moreover, the in vitro antagonistic activity exhibited by B. subtilis highlights its potential for future investigations on disease prevention strategies in Nile tilapia.