Compensatory gain and oxidative response of tilapia rearing at high densities in a biofloc system and transferred to clear water system

Aquaculture has grown a lot in recent years, with tilapia being one of the species with the greatest growth potential. The use of intensive systems, with greater production, biosafety and environmentally correct have been the subject of recent research. The biofloc technology (BFT) has stood out in terms of fish production and performance. The aim of this study was to evaluate the use of a tilapia nursery in BFT for 30 days and/or direct stocking in a clear water system (CW) or 30 days in BFT and then transferred (TRN) to CW. The treatments were as follows: CW 100 (60 days in CW with 100 fish/m3), TRN 750; (30 days in BFT with 750 fish/m3 and 30 days in CW 100 fish/m3), TRN 1500 (30 days in BFT with 1500 fish/m3 and 30 days in CW 100 fish/m3), BFT 750 (60 days in BFT with 750 fish/m3) and BFT 1500 (60 days in BFT with 1500 fish/m3). Water quality, growth, body composition, biochemical and organosomatic parameters, nutrient deposition and thiobarbituric acid reactive substances (TBARS) were evaluated. High ammonia levels and lower pH were observed in the BFT system, this may be associated with a higher density. At 30 days there was a smaller growth of the fish reared at high densities in the BFT, but at 60 days there was a compensatory growth of the fish that were transferred from the BFT to the CW, while fish cultivated for 60 days in BFT with high density showed worse performance indices. There was improvement in the levels of deposition and protein and lipid efficiency in fish transferred from the BFT to CW. An increase in glycogen was also observed in fish cultured for 60 days on BFT and a decrease in proteins and amino acids in the liver of fish cultured for 60 days on BFT. There was a decrease in TBARS in fish cultured in BFT, showing that this system can act as a protector against lipid peroxidation. It is recommended to cultivate tilapia of approximately 2 g in BFT with high density for a period of 30 days and after that, transfer to a production system with lower stocking densities.