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。

Effect of dissolved oxygen on nitrate removal using polycaprolactone as an organic carbon source and biofilm carrier in fixed-film denitrifying reactors

Nitrate-nitrogen（NO_3^--N） always accumulates in commercial recirculating aquaculture systems（RASs） with aerobic nitrification units. The ability to reduce NO_3^--N consistently and confidently could help RASs to become more sustainable. The rich dissolved oxygen（DO）content and sensitive organisms stocked in RASs increase the difficulty of denitrifying technology. A denitrifying process using biologically degradable polymers as an organic carbon source and biofilm carrier was proposed because of its space-efficient nature and strong ability to remove NO_3^--N from RASs. The effect of dissolved oxygen（DO） levels on heterotrophic denitrification in fixed-film reactors filled with polycaprolactone（PCL） was explored in the current experiment. DO conditions in the influent of the denitrifying reactors were set up as follows： the anoxic treatment group（Group A, average DO concentration of 0.28 ± 0.05 mg/L）, the low-oxygen treatment DO group（Group B, average DO concentration of 2.50 ± 0.24 mg/L） and the aerated treatment group（Group C, average DO concentration of 5.63 ± 0.57 mg/L）. Feeding with 200 mg/L of NO_3^--N, the NO_3^--N removal rates were 1.53, 1.60 and 1.42 kg/m3PCL/day in Groups A, B and C, respectively. No significant difference in NO_3^--N removal rates was observed among the three treatments. It was concluded that the inhibitory effects of DO concentrations lower than 6 mg/L on heterotrophic denitrification in the fixed-film reactors filled with PCL can be mitigated.

Performance of feeding Artemia with bioflocs derived from two types of fish solid waste

The production of bioflocs with the solid waste from recirculating aquaculture systems(RAS)and feeding Artemia results in additional nutrient retention and lowers waste discharged from RAS.The solid waste from the drumfilters of two RAS,which stocked European eel(Anguilla anguilla)and Nile tilapia(Oreochromis niloticus),was used as substrate to produce bioflocs in suspended growth reactors,referred to as E-flocs and T-flocs,respectively.Mono-diets consisting of 100%E-flocs and 100%T-flocs were added to culture Artemia,referred as E-Artemia and T-Artemia,respectively,in a laboratory scale test.The efficiency of this feeding regime was investigated.A significant difference was observed in terms of crude protein content(35.59±0.2%)for E-flocs,(29.29±0.95)%for T-flocs,(70.01±0.92)%for E-Artemia and(65.63±0.89)%for T-Artemia.134 out of the total operational taxonomic units(OTUs)were present in E-flocs and T-flocs from the analysis of high-throughput sequencing data.Most of the shared OTUs belonged to cyanobacteria.C18:1n7 of T-flocs was higher than that of E-flocs(P<0.05).C18:2n6 of E-flocs was significantly higher than that of T-flocs(P<0.05).No significant difference was observed in the other fatty acid compositions(P>0.05).The survival rate of E-Artemia was(22±0.02)%,significantly higher than that of T-Artemia(16%±0.02%)(P<0.05).No significant difference was observed between the average body weight of E-Artemia(2.38±0.40 mg)and E-Artemia(2.91±0.21)(P>0.05).The EPA of Artemia fed with E-flocs was(3.00±0.46)%,significantly higher than that of T-Artemia(1.57±0.19%)(P<0.05).This study offers a method for reusing the aquaculture waste,which will be helpful to achieve a zero-pollution discharge for aquaculture systems.