EN
Histopathological examinations of the gills are very useful for the evaluation of the effect of toxic substances on fish and are also valuable in diagnosing certain fish diseases and the study of their pathogenesis. Gill external location and its intimate contact with water means that they are liable to damage by any irritant materials dissolved and suspended in the water and are favored infection sites for viruses, bacteria and parasites. Gill gross pathology and histopathological changes caused by various factors were presented and analyzed in respect to certain toxic substances and some pathological microorganism.