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.