Comparing salinities of 0, 10 and 20 in biofloc genetically improved farmed tilapia (Oreochromis niloticus) production systems

A 150 days(150-d)experiment was carried out to investigate the production efficiency,inorganic nitrogen syndrome and bacteria community of indoor biofloc technology(BFT)systems used to rear genetically improved farmed tilapia(Oreochromis niloticus)under 0(S-0),10(S-10),and 20 salinities(S20).The start-up period for BFT was 50,60 and 80 d for S-0,S-10 and S-20 groups,respectively.At steady state,the total ammonium nitrogen(NH4þ-N)and nitrite nitrogen(NO2-N)were lower than 3.0 mg/L and 0.34 mg/L,respectively and no nitrate-nitrogen(NO3-N)accumulation was observed.The fish survival rate was above 95%for all the groups.The final fish biomass of the S-10 group(35.83±1.08 kg/m^(3))was not significantly different from the S-0(34.79±1.33 kg/m^(3))group but was significantly higher than S-20(32.6±1.04 kg/m3).The feed conversion ratio for the tilapia in S-20 was 1.46,which was higher than the ratio in S-0(1.40)and S-10(1.39)tilapia.There was no significant difference in the crude protein content of the back muscle from tilapia of the three experimental groups.No significant difference in blood parameters,except for aspartate aminotransferase and alkaline phosphatase was observed between the three groups.Evaluation of microorganisms in the three BFT systems revealed that Proteobacteria,Bacteroidetes,and Fusobacteria were the top three at the phylum level in all groups.However,a significant difference was observed at the genus level in the bacteria of the three BFTs at different salinity(P<0.05).©2017 Published by Elsevier B.V.on behalf of Shanghai Ocean University.This is an open access article。