Histological and histochemical study on the alimentary canal in Walking catfish (Claris batrachus) and piranha (Serrasalmus nattereri)

The purpose of this study is to describe the histological and histochemical features of digestive tract intwo aquarium fishes with different types of feeding habits which are omnivorous (Walking catfish) andcarnivorous (piranha), respectively. Five adult Walking catfish (L: 26.4 ± 3.4 cm, W: 265 ± 55 g) and fiveadult piranha (L: 23.6 ± 4.5 cm, W: 247 ± 50 g) were used for this study. The fishes were killed bydecapitation method and small pieces (0.5 cm × 0.5 cm) from the esophagus, cardiac, fundus and pyloricportions of the stomach, proximal, distal parts of intestine and pyloric caeca were fixed by immersion inBouin’s solution. The specimens were processed through routine paraffin embedding technique and cut at 5-7 μm and stained with hematoxylin and eosin, Van Gieson, Verhoof, Alcian blue, PAS, and AB+PAStechnique for different microstructural and microfibrilar structures. The morphological and histochemicalstructures of all specimens were studied with a light microscope and micrographs were prepared. Theesophagus of Walking catfish and piranha are found to have numerous deep longitudinal folds, stratifiedsquamous epithelium with numerous mucous cells which react positively to PAS and AB stains. Taste budsand muscularis mucosa were not seen in the esophagus of both species. The muscularis mucosa wasorganized in longitudinal and circular layers of striated muscular fibers. The mucosa of the stomach wasformed by simple columnar epithelium with folds and gastric pits formed by the invagination of the mucosallayer into the lamina propria. The surface epithelium of the stomach reacted positively to PAS but negativelyto AB staining. The mucosal surface of the intestine in Walking catfish and piranha has numerous folds linedby simple tall columnar cells, along with goblet cells which reacted positive to PAS and AB staining, so thatgoblet cells in the intestine of Walking catfish were significantly more than in piranha. The Caeca pyloricwas found only in piranha and it showed an elongated fold lined with columnar cells and numerous mucouscells which reacted positively to PAS.