The cellular organizations of intestine in Lepidocephalichthys guntea (Hamilton, 1822) have been described by light as well as scanning and transmission electron microscopy. The intestine is short and straight like, marked into anterior, middle and posterior region based on mucosal folds, number and size of columnar epithelial cells and mucous cells, thickness of submucosa and muscularis layer. The mucosa of anterior intestine forms high folds, which are lined with compactly arranged columnar epithelial cells and mucous cells. In the middle intestine, folds are pointless whereas the posterior intestine is without folds. The submucosa is formed of thin layer of connective tissue, contained collagen bundles and blood capillaries, comparatively well developed in the posterior intestine. By scanning electron microscopy, outlines of the luminal surface of anterior and middle intestine is embossed with oval or rounded columnar epithelial cells contained densely packed stubby microridges. The posterior intestine has closely set longitudinal folds characterized with minute blood capillaries and columnar epithelial cells having inconspicuous microridges. Ultrastructurally, the mucosal surface of the intestine consists of mucous cells with electron dense granules and columnar epithelial cells having numerous microvilli, mitochondria, endoplasmic reticulum, lysosomes and Golgi body. Cellular components of the anterior and middle intestine participate in the absorption whereas the presence of enormous blood vessels and capillary net work of posterior intestine probably responsible for air breathing.
The structural characterization of the olfactory epithelium in Pygocentrus nattereri Kner, 1858 was studied with the help of light as well as scanning and transmission electron microscope. The oval shaped olfactory rosette consisted of 26–28 primary lamellae radiated from midline raphe. The olfactory epithelium of each lamella was well distributed by sensory and non-sensory epithelium. The sensory epithelium contained morphologically distinct ciliated and microvillous receptor cells, supporting cells and basal cells. The non-sensory epithelium was made up of labyrinth cells, mucous cells and stratified epithelial cells. According to TEM investigation elongated rod emerging out from dendrite end of the receptor cells in the free space. The dendrite process of microvillous receptor cells contained microvilli. The supporting cells had lobular nucleus with clearly seen electron dense nucleolus. The apex of the ciliated non-sensory cells was broad and provided with plenty of kinocilia. Basal cells provided with oval nucleus and contained small number of secretory granules. The mucous cells were restricted to the non-sensory areas and the nuclei situated basally and filled with about two-third of the vesicles. The functional significance of various cells lining the olfactory epithelium was discussed with mode of life and living of fish concerned.