Comparative histological and histochemical studies on the pancreas of Labeo rohita (Hamilton, 1822), Mystus vittatus (Bloch, 1790) and Notopterus notopterus (Pallas, 1769)

The histological analysis, disposition and histochemical localization of tryptophan were investigated in the pancreas to compare the cellular organization and histochemical characterization in the pancreas of Labeo rohita (Hamilton, 1822), Mystus vittatus (Bloch, 1790) and Notopterus notopterus (Pallas, 1769) having different feeding habits. Histological analysis demonstrated that the exocrine pancreatic tissues were dispersed within the hepatic parenchyma and spleen in L. rohita. Thin septa of connective tissue separated parenchyma of liver and also the spleen from exocrine pancreatic cells. However, in M. vittatus, the discrete pancreatic tissue formed distinct oval or elongated acini interspersed with small area of islet of Langerhans and blood vessels. In N. notopterus, the rhomboidal acinar cells of discrete pancreatic tissue intercalated with comparatively clear and large islet of Langerhans. The exocrine acinar cells in all the three species were provided with prominent nuclei and densely packed zymogen granules. Histochemical localization revealed that the zymogen granules of exocrine acinar cells of all species exhibited varied intensities of tryptophan reaction, the precursor of various pancreatic enzymes which may be related to the food and feeding habits of the fishes under study.