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 in two aquarium fishes with different types of feeding habits which are omnivorous (Walking catfish) and carnivorous (piranha), respectively. Five adult Walking catfish (L: 26.4 ± 3.4 cm, W: 265 ± 55 g) and five adult piranha (L: 23.6 ± 4.5 cm, W: 247 ± 50 g) were used for this study. The fishes were killed by decapitation method and small pieces (0.5 cm ´ 0.5 cm) from the esophagus, cardiac, fundus and pyloric portions of the stomach, proximal, distal parts of intestine and pyloric caeca were fixed by immersion in Bouin’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+PAS technique for different microstructural and microfibrilar structures. The morphological and histochemical structures of all specimens were studied with a light microscope and micrographs were prepared. The esophagus of Walking catfish and piranha are found to have numerous deep longitudinal folds, stratified squamous epithelium with numerous mucous cells which react positively to PAS and AB stains. Taste buds and muscularis mucosa were not seen in the esophagus of both species. The muscularis mucosa was organized in longitudinal and circular layers of striated muscular fibers. The mucosa of the stomach was formed by simple columnar epithelium with folds and gastric pits formed by the invagination of the mucosal layer into the lamina propria. The surface epithelium of the stomach reacted positively to PAS but negatively to AB staining. The mucosal surface of the intestine in Walking catfish and piranha has numerous folds lined by simple tall columnar cells, along with goblet cells which reacted positive to PAS and AB staining, so that goblet cells in the intestine of Walking catfish were significantly more than in piranha. The Caeca pyloric was found only in piranha and it showed an elongated fold lined with columnar cells and numerous mucous cells which reacted positively to PAS.