Growth, digestive activity, welfare, and partial cost-effectiveness of genetically improved farmed tilapia (Oreochromis niloticus) cultured in a recirculating aquaculture system and an indoor biofloc system

• Stocking density of tilapia in biofloc technology (BFT) tank could reach 45 kg m− 3.
• BFT improved growth performance and feed use of cultured tilapia.
• No significant difference of proximate compositions of tilapia cultured in RAS and BFT.
• Suspended flocs have not significant bad effect on tilapia fish welfare.

An 87-d experiment was conducted to investigate the growth, digestive activity, welfare, and partial cost-effectiveness of raising genetically improved farmed tilapia (GIFT) in a recirculating aquaculture system (RAS) and an indoor biofloc technology (BFT) system. The stocking density was 8.06 kg m− 3 in all tanks at the beginning of the study, and reached 44.95 kg m− 3 in the BFT tanks and 36.87 kg m− 3 in the RAS tanks at the end of the study. The individual fish weight at harvest was 22% higher in the BFT fish than in the RAS fish. The total weight gain and specific growth rate of the BFT fish were, respectively, 128% and 112% higher than those of the RAS fish. The feed conversion ratio for BFT was 18% lower than that for the RAS. There was no significant difference in the crude protein (CP) and crude lipid (CL) content from the fish back muscle between the fish in the RAS and the BFT tanks. The CP and CL contents of the BFT fish were 30.90 ± 9.04% and 1.27 ± 0.61%, respectively. The activities of lipase in the stomach and intestine showed substantial differences between the RAS and the BFT fish, whereas the activity of protease did not. There was no significant difference in the activities of alkaline phosphatase (ALP), lysozyme (LYZ) of the hepatopancreas, head kidneys, and serum between treatments. The total superoxide dismutase (T-SOD) activity of the serum of the BFT fish was considerably higher than that of the RAS fish. The accumulations of ammonium nitrogen (highest: 60 ± 0.45 mg L− 1) and nitrite nitrogen (highest: 119 ± 2.01 mg L− 1) were observed in the BFT tanks. The phosphate concentration in the BFT tanks (< 4.01 ± 0.34 mg L− 1) was substantially lower than that in the RAS tanks. The fish survival rate was 100% for both the RAS and BFT. Partial analysis of the cost-effectiveness of operations under experimental conditions revealed that the BFT model was more effective than the RAS in tilapia culture.