Comparative studies on histology and histochemistry of pancreas between Labeo calbasu (Hamilton, 1822) and Mystus gulio (Hamilton, 1822)

The cellular architecture and histochemical nature of the enzyme secretory acinar cells of pancreas have been investigated in two species of fish, Labeo calbasu and Mystus gulio having different feeding habits. Histological analysis illustrates that the exocrine pancreatic tissues are scattered within the hepatic parenchyma as hepatopancreas and spleen as spleenpancreas in L. calbasu. The structural analysis also shows that exocrine as well as endocrine pancreatic tissues are also diffused in the adipose tissues in between the intestinal coiling of L. calbasu. In M. gulio the discrete pancreatic tissue is attached to the outer wall of the stomach and formed cluster of acini interspersed with small areas of islet of Langerhans and blood vessels. The exocrine pancreatic acinar cells are provided with conspicuous nuclei and densely packed acidophilic zymogen granules. The endocrine component of pancreas, islet of Langerhans is encircled by a thin connective tissue and comprised of α, β and δ cells. Different cell types in the islets are differentiated based mainly upon their shape, position, staining intensity and density of the cytoplasmic secretory granules. α cells contain sparse cytoplasm and densely stained nuclei, are generally located to the periphery of the islet Aldehyde fuchsin positive β cells bear spherical nucleus and granular cytoplasm, are in the center of islet of Langerhans contacted with blood vessels. δ cells are few in number with light stained nuclei disperse in the pancreatic islet. Histochemical detection displays that the zymogen granules of exocrine acinar cells showing variegated intensities of tryptophan reaction, the precursor of numerous pancreatic enzymes which probably related to the food and feeding habits of the fishes concerned. The zymogen granules are larger in size and heavily deposited in the acinar cells of hepatopancreas of L. calbasu in comparison to M. gulio may be correlated with the herbivorous feeding habit in respect to secretion of digestive enzymes.