The structural characterization and function of the stomach in the omnivore Pygocentrus nattereri were described using light and scanning electron microscopy. The sac-like stomach was morphologically divided into the cardiac and pyloric regions. The histological structure of the stomach consisted of four layers of the mucosa, submucosa, muscularis, and serosa. The superficial epithelium of the cardiac stomach was lined with columnar epithelial cells and the glandular epithelium contained numerous gastric glands. Gastric glands were completely absent in the pyloric portion. The mucosal surface of the stomach was a meshwork of various folds, provided with oval or rounded columnar epithelial cells which were densely packed with short, stubby microvilli. The occasional presence of conspicuous gastric pits was surrounded by epithelial cells. The localization and chemical nature of acid and neutral mucins in the various cells of the stomach was studied by employing combined the Alcian Blue-Periodic Acid Schiff (AB-PAS) technique. The deposition of glycogen was detected in the gastric glands as well as in the epithelial lining of the stomach. The utmost reactions for protein and tryptophan were recorded in the gastric glands of mucosa. The cellular organization and histochemical characterization of the stomach are discussed in relation to the feeding and digestion of the fish concerned.
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.