FIGURE 3 in Morphological study of the digestive tract of the cardinal tetra, Paracheirodon axelrodi (Characiformes: Characidae)

FIGURE 3 | Histological sections of the digestive tract of Paracheirodon axelrodi, stained with Masson Trichrome (MT) (A,B,F,G), Periodic AcidSchiff (PAS) (C) and Alcian Blue (AB) (D,E). A. Cross section of the pyloric portion of the stomach, showing the CE mucosa and a layer of loose connective tissue (asterisk) under the epithelium. Note the absence of GG and a great development of the inner circular layer of SM. B. Cross section of a pyloric cecum, showing mucosal CE cells arranged in a brush border fashion and with numerous folds, and a thin layer of SM. Part of the pyloric stomach can be seen in the upper right corner. A portion of the pancreas (P) can be seen in the upper and lower corners. C. Cross section of intestine showing the PAS positive goblet cells (GCs) (arrowheads) with cytoplasm filled with glycoconjugates. The PAS reaction for neutral glycoconjugates produces an intense purple stain in the mucous granules of GCs and emphasizes the brush border of the enterocytes (arrow). D-E. Pyloric cecum (D) and intestine (E) showing AB positive GCs, with a similar distribution pattern in the epithelium. Thanks to the AB technique for acid mucosubstances, GCs show a strong positive blue staining. F. Pancreas section. The exocrine pancreas is formed by acini (segmented line), which are made up of a group of pyramidal-shaped secretory cells, called acinar cells. Towards the central part of the acinus, a small afferent vein is observed (white arrow). A prominent feature of acinar cells is the presence in their apical regions of aggregated bright eosinophilic zymogen granules (asterisk) that face the narrow lumen. The endocrine pancreas is formed by the Islets of Langerhans (IsL) composed of small cells with a pale-stained granular cytoplasm, in contrast to the larger acinar cells of the exocrine gland, which stain more strongly. On the left is a pancreatic duct (black star) with simple cuboidal epithelium. G. Liver (L) and pancreas (P) section. Many fish livers contain diffuse exocrine pancreatic tissue and are therefore called hepatopancreas. The liver showed polyhedral hepatocytes (asteriks) with a granular and poorly stained cytoplasm, the nuclei are spherical and centrally located presenting well delineated nucleoli. On the left is the smooth muscle layer (SM) of a portion of the intestine. CE, simple columnar epithelium; GCs, goblet cells; GG, gastric glands; SM, smooth muscle.