Using the scanning electron microscope, the gills of Schizothorax curvifrons have been studied after carrying out their primary fixation in 2.5% glutaraldehyde in 0.1 M sodiumcacodylate buffer (pH 7.3) for 24 h at 0-4 degrees C and secondary fixation in 1-4% osmiumtetraoxide in 0.1 M sodiumcacodylate buffer (pH 7.3) for 1-2 h at 0-4 degrees C. The gills are observed to comprise of gill arch, gill rakers having minute projections on their inner sides and gill filaments. The filaments originating from the gill arch are in a linear fashion and equidistant from each other, bearing secondary lamellae on both sides of the filament axis and each lamellae running parallel to the adjacent lamellae. The filament epithelium is found to be equipped with pavement cells, mucous cells and chloride cells. The pavement cells have smooth surface with sparse and irregular microridges defining their cell limits. The mucous cells are mainly found on the leading and trailing edges of the filament and the chloride cells are located close to the onset of secondary lamellae. The possible roles of these structures and cells in relation to respiration, water flow and feeding are discussed, setting thereby a platform for further studies in relation to pathology, pollution and stress conditions in aquaculture, natural and polluted environments.
The present study aimed to investigate the macroscopic structure of the gastrointestinal tract (GIT) of Schizothorax esocinus Heckel, 1838. The surface architecture of the buccopharynx, oesophagus and the entire intestinal tract of S. esocinus has been examined under scanning electron microscope (SEM) after fixing in 2.5% glutaraldehyde buffered with 0.1 M sodium cacodylate at pH 7.3 for 18–48 hours and post-fixation for two hours at room temperature in 1% osmium tetra oxide buffered at pH 7.3 with 0.1 M cacodylate. The mucosal surface of buccopharynx, esophagus, intestinal bulb, and intestine reveal prominent longitudinal major or primary mucosal folds which are further subdivided into the series of irregular and well-circumscribed folds called minor or secondary folds. However, in the intestinal bulb and intestine, the longitudinal major or primary folds themselves form wavy or zigzagging patterns along the mucosal surface. The fine structure of the surface epithelium further shows that the apical surfaces of the epithelial cells are ped with finger-print like microridges, arranged in various patterns and regularly spaced. The rectal mucosa, on the other hand, displays a highly irregular type of major mucosal folds. The separation can’t be seen between major mucosal folds. A thin film of mucous spread over the mucosal folds and the numerous pores through which mucous cells release their content has also been noted along the rectal mucosa. This investigation suggests the possible role of different digestive organs in relation to feeding, digestion, storage, absorption, and various other physiological processes, thereby providing a knowledge necessary to the understanding of pathological or physiological alterations in both aquaculture and natural environment.
SummaryThe 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.
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