Histopathological Evidence of Regeneration following Hepatotoxic Effects of the Cyanotoxin Microcystin-LR in the Hardhead Catfish and Gulf Killifish

Abstract

The cyanobacterial toxin microcystin-LR (MC-LR) causes liver damage in several freshwater fish species. In the present study, two estuarine species, hardhead catfish Arius felis and gulf killifish Fundulus grandis, were injected intraperitoneally with MC-LR at 45?300 μg/kg and their livers examined histopathologically for up to 23 d postinjection (PI) in the catfish and 5 d PI in the killifish. The livers from both species exhibited extensive, diffuse hepatocellular necrosis by 6 h PI. The necrosis persisted, and by day 2 large numbers of basophilic cells had emerged throughout the liver parenchyma. These cells occurred individually or in small clusters. By 72 h, the basophilic cells appeared to be highly proliferative with numerous mitotic figures and were arranged in cords and tubules similar to mature hepatic parenchyma. Regeneration of the liver parenchyma was noted in gulf killifish at 5 d PI, as tracts of basophilic cells were still evident. In hardhead catfish, there were no signs of necrosis or proliferating basophilic cells by 9 d PI, and the hepatic parenchyma appeared normal except for the vacuolation of many hepatocytes and some areas of hepatic megalocytosis. The degenerative changes in the two species studied were similar to but more pronounced than those observed in freshwater fish species exposed to MC-LR. Evidence of regeneration from the hepatotoxic effects of MC-LR suggests that the toxin can be used to study regenerative processes in fish livers.