Lethal doses of ammonia on the late-stage larvae of Chinese mitten-handed crab, Eriocheir sinensis (H. Milne-Edwards), (Decapoda: Grapsidae) reared in the laboratory

Abstract

Four successive life stages (zoea-III, zoea-IV, zoea-V and megalopa) of the Chinese mitten-handed crab, Eriocheir sinensis (H. Milne-Edwards), were exposed to ammonia in a series of short-term bioassays with the static-renewal method at 22 °C, pH 8.0 and 25‰ salinity. The greatest sensitivity was observed in the zoea-III stage. The 24-h LC50 values for zoea-III, zoea-IV, zoea-V and megalopa were 32.8, 73.1 84.0 and 90.1 mg L-1 for NH3 + NH4+, and 1.11, 2.36, 2.77 and 3.18 mg L-1 for NH3, respectively. The 72-h LC50 values for zoea-III, zoea-IV and zoea-V were 11.9, 23.6 and 38.2 mg L-1 for NH3 + NH4/+, and 0.40, 0.76 and 1.26 mg L-1 for NH3, respectively. The 96-h LC50 values for megalopa were 37.3 mg L-1 for NH3 + NH4/+ and 1.31 mgL-1 for NH3. It was found that ammonia tolerance increased with larval development from zoea-III to megalopa, especially from zoea-III to zoea-IV and from zoea-IV to zoea-V. A comparison of safe levels of ammonia among the different life stages indicated that all stages were significantly different with respect to safe levels of ammonia (P < 0.05) except zoea-V and megalopa, which had the highest safe levels. In general, both the larvae and juveniles of E. sinensis are less resistant to ammonia than those of other crustacean species studied so far.