Acute toxicity of ammonia to the early stage-larvae and juveniles of Eriocheir sinensis H. Milne-Edwards, 1853 (Decapoda: Grapsidae) reared in the laboratory

Abstract

Static-renewal bioassays were performed to evaluate the acute toxicity of ammonia to Eriocheir sinensis (H. Milne-Edwards) at three growing stages, namely zoea-I, zoea-II, and juvenile (0.06 g wet weight per crab). The 24 h LC50 values were 13.3, 20.2, and 109.3 mg (NH3 + NH4 +) l-1 (0.47, 0.71, and 3.10 mg NH3 l-1), the 48 h LC50 values being 6.8, 10.3, and 60.9 mg (NH3 + NH4 +)l-1 (0.24, 0.36, and 1.73 mg NH3 l-1), while the 72 h LC50 values were 5.7, 7.6, and 45.3 mg (NH3 + NH4 +) l-1 (0.20, 0.27, and 1.29 mg NH3 l-1) for zoea-I, zoea-II, and juveniles, respectively. The 96 h LC50 value for juveniles was 31.6 mg (NH3 + NH4 +)l-1 (0.90 mg NH3 l-1). It was evident that the tolerance to ammonia increased during the same exposure time as the larvae developed to juveniles and decreased with prolonged exposure time. Compared with larvae, juveniles were more sensitive to the fluctuation of ambient ammonia concentrations in the certain range within which partial kills took place. The 'safe level' of ammonia based on the 96 h LC50 value and an application factor of 0.1 was 3.16 mg (NH3 + NH4 +)l-1 (0.09 mg NH3 l-1) for juveniles and those for zoea-I and zoea-II were 0.57 and 0.76 mg (NH3 + NH4 +)l-1 (0.02 and 0.03 mg NH3 l-1) based on 72 h LC50 values.