Pathologic studies on the sublethal effects of phenol on grass carp [ctenopharyngodon idella]

The pathological effect of long-term exposure to pure phenol was studied in grass carp. The highest level of phenol which could be tolerated by carp was 15 ppm. At this concentration, the associated clinical signs were nervous in their nature, began as excitation and ended by depression. The gross lesions were color changes of the skin, increased mucous secretion from gills and hyperemia of the viscera, especially of the brain. The histopathologic findings were degenerative and necrotic changes in gills, muscles, spleen, kidneys, liver, heart and brain which, by time, became less evident or absent. The clinical signs and lesions disappeared after the transfer of the affected fish to clean water