Effect of purified microcystin on oxidative stress of silver carp Hypophthalmichthys molitrix larvae under different ammonia concentrations

During the degradation of Microcystis spp. blooms, ammonia and microcystin are released into water column at the same time, which may impact aquatic organisms. This study assessed the responses of oxidative stress to a combination of ammonia and microcystin in larval fish. Newly-hatched larvae and 21-day-old larvae of silver carp Hypophthalmichthys molitrix were exposed to solutions with different concentrations of ammonia (NH₃–N) and microcystin-LR (MC-LR). Results indicated significant interaction between NH₃–N and MC-LR on glutathione (GSH) and malondialdehyde (MDA) levels in newly-hatched larvae. In the 21-day-old larvae, MDA fluctuated significantly with time and the two toxins, and significant interactions were detected among any two or three factors (time, NH₃–N, MC-LR); the superoxide dismutase (SOD) and GSH changed significantly with time and concentrations of toxins and were time or dose-dependent on NH₃–N and MC-LR exposure; results also indicated significant interaction on SOD or GSH among any two or three factors.