Abstract: We studied the growth of strain NB5 isolated from nitrifying bacteria and its removal effect on ammonia nitrogen (NH₄ ⁺-N) and nitrite nitrogen (NO₂ ⁻-N) under different aquaculture conditions, and identified this bacterium. The results show that strain NB5 grew well at salinity of 25−45, pH of 6.0−9.0, temperature of 15−35 ℃ and ventilations of 1−2 L·min⁻¹ (P>0.05). At salinities of 45, 35 and 25, the maximum removal rates of NH₄ ⁺-N were 96.24%, 88.93% and 75.08%, respectively. At pHs of 7.5 and 9.0, they were 99.53% and 99.37%, respectively. At temperatures of 30, 25, 15 and 35 ℃, they were 99.53%, 97.22%, 97.29% and 71.26%, respectively. At ventilations of 2 and 1 L·min⁻¹, they were 99.87% and 99.82%, respectively. Under the above conditions, the maximum removal rates of NH₄ ⁺-N were significantly higher than those of the control group and the other groups (P<0.05). Strain NB5 had no significant effect on NO₂ ⁻-N concentration under different aquaculture conditions (P>0.05). By 16S rDNA sequence analysis, strain NB5 was identified as Nitratireductor aquimarinus. The results indicate that strain NB5 has good environmental adaptability, especially suitable for aquaculture pond environment at medium and high salinities (25−45).