Subchronic oral toxicity of microcystin in common carp (Cyprinus carpio L.) exposed to Microcystis under laboratory conditions.

The subchronic oral toxicity of microcystin in common carp (Cyprinus carpio L.) was investigated in this study. The fish (mean body weight of 322+/-36 g, n=10) were orally exposed to Microcystis by feeding with bloom scum at a dose of 50 microg microcystins/kg body weight under laboratory conditions for 28 days. Growth assay results showed that microcystin could completely inhibit the growth of carp, but failed to change the fish hepatosomatic index. Ultrastructural examination by electron microscope revealed severe damage in hepatocytes derived from the treated fish. Serum biochemical assays with commercial kits indicated that alanine aminotransferase and aspartate aminotransferase activities were significantly increased as compared to control levels, but gamma-glutamyl transferase, alkaline phosphatase and lactate dehydrogenase activities remained unchanged. Protein phosphatase inhibition assay revealed that the microcystin concentrations were 261.0+/-108.3 ng microcystin-LR equivalent/g fresh weight in hepatopancreas and 38.3+/-12.3 ng microcystin-LR equivalent/g fresh weight in muscle. The latter is above the limit recommended by the World Health Organization for human consumption. Therefore, we recommend that a warning system be instituted for announcing the occurrence of microcystin-producing water bloom and the possible risk of human intoxication.