Effects of restricted feeding levels and stocking densities on water quality, growth performance, body composition and mucosal innate immunity of Nile tilapia (Oreochromis niloticus) fry in a biofloc system

In aquaculture feed accounts for more than 50% of current costs. Biofloc has the potential to compensate for food reduction, so restricted feeding levels should be investigated to decrease food consumption. The present study conducted to evaluate the effect of restricted feeding levels and stocking densities on water quality, growth performance, body composition and mucosal innate immunity of Nile tilapia (Oreochromis niloticus) fry in biofloc system (BFT). A 5*2 factorial experimental design was used with five restricted feeding levels (0, 15, 30, 45 and 100) and 2 stocking densities(500 fish/m3 and 1000fish/m3) comprising 10 treatments for BFT and for each density there were clear water (CW) system as control with three replicates. Fry with initial weight of 3.2 ± 0.05 g were stocked in tank(40 L), fed three times a day at 8:00, 12:00 and 16:00. Molasses was added to BFT treatments as organic carbon source at a C/N ratio of 15. Results showed that, growth indices (WG, DGR, SGR, FCR), water quality parameters (TAN, NO2, NO3, settled solids and total suspended solids), as well as innate immunity (Total immunoglobulin, Lysozyme and Catalase activity) were improved in biofloc system compared to the CW system. The reduction of feeding rate resulted in significantly decreasing growth performances and immunity among biofloc groups (p