Acute toxic effects of nitrite and non-ion ammonia on Fenneropenaeus chinensis at different dissolved oxygen levels

The acute toxic effects of nitrite and non-ion ammonia on Fenneropenaeus chinensis were studied at normal(5.5～6.0 mg/L)and hyperoxic(10～12 mg/L)dissolved ox- ygen levels.The results showed that the 48h and 96h median lethal concentrations(LC50) 95% confidence limits)of nitrite for F.chinensis at normal oxygen level were 69.43mg/L 58.53～82.36 mg/L)and 43.80 mg/L(37.57～51.06 mg/L),respectively;and those of non- ion ammonia were 1.36 mg/L(1.15～1.61 mg/L)and 0.98 mg/L(0.83～1.16 rag/L),re- spectively.However,under hyperoxic conditions,the 48h and 96h LC50(95% confidence lim- its)of nitrite for F.chinensis were 94.80 mg/L(79.77～112.66 mg/L)and 58.64 mg/L (51.40～66.90 mg/L),respectively;and those of non-ion ammonia were 2.37 mg/L(2.05～2.75 mg/L)and 1.52 mg/L(1.30～1.77 mg/L),respectively.Both nitrite and ammonia-nitro- gen were found to be toxic to F.chinensis;yet the toxic effects of non-ion ammonia were more significant than that of nitrite,irrespective of oxygen levels.At the same time,F.chinensis could tolerate much higher concentrations of nitrite or non-ion ammonia under hyperoxic condi- tions;and compared to nitrite,the toxicity of non-ion ammonia was more easily alleviated by the hyperoxic conditions.