Abstract
Macrognathus aculeatus (Bl.) and Mastacembelus pancalus (Lac.) (Family: Mastacembelidae) are considered to be the most delicious fish in Andhra Pradesh due to the tenderness of their muscles. The metacercariae of Clinostomum mastacembeli Jaiswal, 1957 are found infesting the oesophagus of these fishes heavily. During present studies, histopathological changes caused due to the encystment of metacercariae of C. mastacembeli in the oesophagus of these fishes were observed. The four layers of the oesophagus namely; serosa, muscualris layer, submucosa and mucosa were found severely affected. Histopathological changes included decrease in the lumen diameter of the oesophagus, atrophy and necrosis of epithelial cells of serosa layer, shrinkage of villi due to thickening of muscularis layer and formation of small vacuoles in the sub-mucosal layers.