Influence of Varied Carbon Sources and Carbon-Nitrogen Ratio on Microbial Community in a Biofloc-Based Culture System and Their Effects on Growth Performance, Proximate Composition, Hematology and Oxidative Stress in Nile Tilapia

This study investigates the influence of varied carbon sources and carbon-nitrogen ratio on microbial community in a biofloc-based culture system and their effects on growth performance, proximate composition, hematology, and oxidative stress in Nile tilapia. The experiment involved three different carbon-nitrogen ratios (10:1, 15:1, 20:1) and two carbohydrate sources (molasses: ML-10, ML-15, ML-20, starch: S-10, S-15, and S-20) with three replicates each. A diet containing 25% crude protein was fed to fish in 18 experimental units for 120 days. Carbohydrate supplementation significantly increased the total heterotrophic bacterial (THB) count from C/N10 to C/N20 while decreasing pH, total ammonia nitrogen, and nitrate nitrogen contents. In addition, growth was considerably greater in the ML-10 and ML-15 groups compared to the C/N20 group. Increasing the C/N ratio increased body protein and ash, decreased lipid contents, and increased the activities of lysozyme, SOD, CAT, and GPx. Finally, the C/N10 and C/N15 groups showed significantly lower GLU and COR concentrations in biofloc compared to the C/N20 group. Furthermore, increasing the C/N ratio up to 15 resulted in improved outcomes in terms of Hb, WBCs, RBCs, and Ht content. Overall, the utilization of the C/N15 group resulted in suitable growth, proximate composition, and immunity in Nile tilapia.