The biofloc technology (BFT) in indoor tanks: Water quality, biofloc composition, and growth and welfare of Nile tilapia (Oreochromis niloticus)

The present study evaluates the biofloc technology (BFT) in light-limited tank culture of Nile tilapia (Oreochromis niloticus). Two biofloc treatments and one control were managed in 250 1 indoor tanks: BFT fed a diet of 35% crude protein (CP), BFT fed a diet of 24% CP, and clean water control without biofloc with 35% CP. BFT tanks were aerated and agitated using a dome diffuser. Three kg of Nile tilapia were stocked in each tank. Feed was applied at 1.5% of the total fish biomass daily in each tank. Wheat flour was added in BFT tanks to maintain an optimum C:N ratio for heterotrophic production. The total suspended solid (TSS) level was maintained at around 500 mg l(-1) in BFT tanks. The nutritional quality of biofloc was appropriate for tilapias. Fish survival was 100%. Net fish production was 45% higher in the BFT tanks than in the control tanks confirming the utilization of biofloc by fish as food. There was no difference in fish growth/production between 35% and 24% CP fed tanks under BFT. Welfare indicators in terms of fin condition, gill histology, proximate composition, blood haematocrit and plasma cortisol levels were compared and no significant differences between BFT and control tanks were recorded indicating no increased fish stress due to the presence of biofloc. However, overall fish growth and production was poor in terms of commercial feasibility. A modified system design that would allow enhanced feed and biofloc utilization is proposed