Effects of fermented corn cob on growth performance, digestive enzyme, immune response, and gene expression of nile tilapia (Oreochromis niloticus) raised in biofloc system.

Utilizing agricultural by-products through fermentation presents a sustainable strategy to enhance the nutritional value of aquaculture feeds. This study aimed to evaluate the effects of different dietary levels of fermented corn cob (FCC) on growth performance, digestive enzyme activities, immune responses, and gene expression in Nile tilapia cultured in a biofloc environment. Three hundred Nile tilapia fingerlings (average of 37.58 ± 0.12 g) were randomly allocated to five dietary treatments (0, 2.5, 5, 10, and 20 g kg FCC) with three replicates per treatment. Fish were reared in 150-L aquaria under biofloc conditions for eight weeks. Growth performance, digestive enzyme activities, innate immune parameters in skin mucus and serum, as well as gene expressions were measured. The results indicated that fish fed diets containing 10-20 g kg FCC exhibited significantly greater final weight, weight gain, and specific growth rate compared to the control group (P < 0.05), along with improved feed conversion ratios. Digestive enzyme activities were significantly enhanced in fish receiving FCC10 and FCC20 diets. Similarly, innate immune responses, including lysozyme, peroxidase, and complement activity, were significantly upregulated in both skin mucus and serum of FCC-fed fish. At the molecular level, the expression of growth-related genes (ghrelin, galanin, EF-α, and NPY-α), immune-related genes (il-1β, MHC II-α, TNF-α, and NFκB), antioxidant-related genes (GPX, hsp70, and nrf2) was significantly upregulated in fish fed FCC10 and FCC20 diets. Overall, dietary supplementation with 10-20 g kg FCC under biofloc conditions significantly enhanced growth performance, digestive function, innate immunity, and gene expression profiles in Nile tilapia, supporting the potential application of FCC as a sustainable functional feed additive to promote health and productivity in aquaculture.