Modifications in the surface organisation of the epidermis on the outer surface of the operculum and the epithelium lining the inner surface of the operculum in certain fresh water teleosts

The outer surface of the opercular epidermis (OE) and the epithelium lining the inner surface of the operculum (EISO) of Macrognathus aculeatum, Colisa fasciata and Glossogobius giuris was investigated using scanning electron microscopy to unravel their surface ultrastructure. In the fish species investigated, the OE is thick, compared to the EISO. The OE and the EISO remain covered with a mosaic pavement of irregularly polygonal epithelial cells. The free surface of the epithelial cells is thrown into a series of microridges. Modifications in the pattern of microridges could be caused by various intrinsic or extrinsic factors. Interspersed between the epithelial cells in the OE mucous cell pores, mitochondria-rich cells, taste buds and superficial neuromasts could be located. In the EISO, in contrast, taste buds and neuromasts are absent. The modifications in the surface organisations at the OE and EISO in different fish species have been associated to perform a variety of functions and have been discussed in the light of the varied conditions experienced by them.