An enhanced bioreactor was designed according to the highly effective interception principle of biofilm in recirculating aquaculture systems(RAS)by inoculating nitrifying and denitrifying bacteria to the elastic fiber carriers on which biofilms could be observed in situ 6 weeks after inoculating.The impact of hydraulic retention time(HRT)and water temperature(WT)on the purifying effects of enhanced bioreactor on wastewater of RAS was investigated.The result showed that HRT and WT significantly impacted the purifying effect of the bioreactor on wastewater(P<0.05).After analysis of significant differences between HRT and WT within removal rate of COD_Mn,TN and NH ₄-N,and considering run-time,cost and operational easiness of bioreactor,it was concluded that 18 h of HRT and 30 ℃ were the best operating conditions.The bioreactor was operated stably for 25 days under these conditions,the average removal rate of COD_Mn,TN and NH ₄-N reached 44.18%,51.31% and 82.08%,respectively.In addition,the cultivable microorganisms in the biofilm of the enhanced bioreactor were detected regularly throughout the 25 days of experimental time.As the biofilm developed,the biomass of all kinds of cultivable microorganisms rose,average levels of nitrifying bacteria grew from 35.91?10⁴ CFU/mg to 89.43?10⁴ CFU/mg,nitroso-bacteria from 25.75?10⁴ CFU/mg to 61.65?10⁴ CFU/mg and denitrifying bacteria from 14.23?10⁴ CFU/mg to 100.95?10⁴ CFU/mg.Nitrifying and nitroso-bacteria dominated among cultivable microorganisms(59.95%-81.25%).Denitrifying bacteria were constantly adsorbed,colonized and successfully reproduced on the surface of elastic fiber carriers,which made biofilms more mature and stable(the removal rate of TN and NH ₄-N reached respectively 51.31% and 82.08%).The results of present study revealed that the enhanced bioreactor plays an important role in the removal of COD_Mn,TN and NH ₄-N in wastewater of RAS.