Epithelium of the Intestinal Tract of a Freshwater Teleost, Schizothorax curvifrons Heckel (Cyprinidae, Cypriniformes, Pisces): An Ultrastructural Study

Transmission electron microscopic study has been conducted on the epithelium of an unaltered intestinal tract of the snow trout, Schizothorax curvifrons. The ultrastructural analysis reveals that the epithelium comprises of enterocytes, goblet cells and rodlet cells. The enterocytes with basal nuclei were joined at their apical surfaces by desmosomes and microvilli forming a brush border were found on their apical plasma membrane, with a steady decrease in the length and density of the microvilli from the intestinal bulb towards the rectum. Spherical blebs were observed on the dense tips of the microvilli of the intestinal enterocytes. Distinct invaginations of the plasmalemma were found below the terminal net which is formed by the deep projection of the microfibrils of the microvilli in the apical cytosol. Endoplasmic reticulum, low density lipid droplets, heteromorphic mitochondria, and lysosomes were found scattered in the supranuclear cytosol of the enterocytes. The mucous secreting goblet cells interspersed between the enterocytes were occupied by tightly packed mucous globules of varying electrodensity. The rodlet cells were encountered only in the intestinal epithelium. The possible roles of the enterocytes and associated structures, goblet cells and rodlet cells have been discussed in this paper.