Liver Histopathology of the Fish Brachydanio Rerio Hamilton-buchman after Acute Exposure to Sublethal Levels of the Organophosphate Dimethoate

Among the new substances that were synthesised by the chemical industlY during the last decades, with the aim to improve human prosperity, some cause negative effects on non target organisms like fish. Among the pesticides, the organophosphates (OP) are widely used in cattle management, agriculture and aquaculture activi ties. Brachydania reria Hamilton-Buchman, 1822 is used world-wide in fishtests for the establishment of the lethal levels of pesticides. Nevertheless, these fi sh show morphological changes in their hepatocytes when exposed experimentally for 24 hours to the sublethal dose of 0.025 fli /l of the OP Dimethoate 500, in ac ute tests. Eight hours after exposure, a high density ofeells with cytoplasmic granulation is seen as well as focal necrosis. The main changes that occurred in the first 24 hours of exposure we re the loss of the typical polygonal ce ll shape and of detec tab le cell limits, lateral migration of nuclei, nuclear size and shape, condensati on of chromatin and pycnosis, increased cytoplasmic granulation followed by vacuo li sati on. After 48 hours in clean water, 72 hours ti'om contaminati on, besides significant morphologica l changes and necrosis, focal regeneration of the hepatocytes, canaliculi , ducts and sinusoids were seen. Even having been exposed to the half of the dose considered as safe according to the general pesticide allowance rules, significant changes of the liver ti ssue were obselved.