Nitrogenous pollutants including ammonia, nitrite, and nitrate are a widespread concern in natural waters and aquaculture. In the present study, the toxicity of ammonia, nitrite, and nitrate to rare minnow (Gobiocypris rarus) in the early life stage were evaluated by 2 short-term toxicity tests. In the short-term toxicity test, conducted on embryo and sac-fry stages, 30 fertilized eggs with 3 replicates were randomly exposed to varying levels of ammonia, nitrite, and nitrate until 3 d posthatch (dph). In the 7-d larval subchronic toxicity test, 30 newly hatched larvae with 3 replicates were randomly exposed to varying levels of ammonia, nitrite, and nitrate until 7 dph. The results showed that the 7-d larval subchronic toxicity test was more sensitive than the short-term toxicity test on embryo and sac-fry stages. Both toxicity tests revealed that ammonia was most toxic to rare minnows, followed by nitrite and nitrate. High levels of ammonia, nitrite, and nitrate decreased growth, retarded development, and increased mortality. The no-observed-effect concentrations of ammonia, nitrite, and nitrate for larval growth were 2.49 mg L À1 , 13.33 mg L À1 , and 19.95 mg L À1 nitrogen, respectively. The present study's results demonstrate that nitrogenous pollutants pose a threat to wild populations of rare minnows and provide useful information for establishing water quality criteria for this laboratory fish.

Dimethyl sulfoxide (DMSO), a widely used carrier solvent, can be toxic to test organisms and has species-specific sensitivity. In this study, the developmental toxicity and stress protein responses of DMSO to rare minnow (Gobiocypris rarus) and zebrafish (Danio rerio) with two tests were compared in the early life stage. In the first test, fertilized eggs were exposed to 0%, 0.0001%, 0.001%, 0.01%, 0.1%, 1.0%, 1.5%, and 2.0% v/v of DMSO until 3 days post hatching. In the second test, larvae from 0 to 8 d were exposed to 2% DMSO until 4 days. Our results showed that DMSO was toxic to rare minnow and zebrafish on multiple indexes, and the no-observed-effect concentrations of DMSO in both species were 1.0% and 0.001% for developmental toxicity analysis and stress protein analysis, respectively. Furthermore, rare minnow larvae were more sensitive than zebrafish to DMSO for spinal malformation. The sensitive period for induction of spinal malformation by DMSO was 0-7 d after hatch (dah) for rare minnow and 0-4 dah for zebrafish. Together, these results will provide support to the use of DMSO in ecotoxicological studies using rare minnow and will contribute to a better understanding of the toxicity of DMSO.

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