Mucous Cells in the Gills of Snow Trout, Schizothorax curvifrons Heckel (Pisces, Cypriniformes, Cyprinidae)

Abstract

The ultrastructural and histochemical characteristics of mucous cells and their functional significance in the gills of Schizothorax curvifrons were studied with the objectives that this study could serve as a basis for further studies in relation to histopathology, aquatic toxicology and stress conditions in aquaculture and natural or polluted environments. The electron microscopical analysis of the gills following fixation in Karnovsky's fluid and post fixation in osmium tetraoxide revealed that the mucous cells were covered by epithelial cells and their major part was occupied by firmly arranged large mucous globules of different electrodensities, displacing their nuclei towards the basal position. The cytoplasmic extensions and islets among the mucous globules and the cellular interdigitations between mucous cells and neighbouring cells were present and the release of mucin by exocytosis was also observed. Utilizing histochemical techniques that included methods of periodic acid Schiff (PAS) reaction and alcian blue method (AB pH 2.5) for localization of neutral and acid mucopolysaccharide secreting mucous cells showed that the gill epithelium was lined by mucous cells which were found to be PAS and AB positive, confirming the presence of both neutral mucous cells secreting hexose containing mucosubstances and acidic mucous cells secreting weakly acidic sulphated mucosubstances and sialomucins. The possible roles of the mucous cells and the products secreted by them have been discussed in this paper.