ABSTRACT
The liver is a large digestive gland composed of parenchymal cells and lattice fibers. The fish hepatic parenchyma is not arranged into distinct lobules. Three patterns of organization of fish hepatic parenchyma are recognized. The first pattern is composed of hepatocytes that are radially arranged around the central vein. The second arrangement called a tubular pattern, in which the sinusoids form a network around the hepatic tubules. The third arrangement is present in some fresh and marine teleosts, the hepatocytes lie in anastomosing lamina around the central vein. Serial paraffin section of the liver identified different kinds of vascular–biliary structures as follows: first, pancreatic–venous–biliary–arteriolar tracts (P-VBAT); second, venous–biliary–arteriolar tracts (VBAT); third, pancreatic–venous–biliary tracts (P-VBT); fourth, venous–biliary tracts (VBT); fifth, venous–arteriolar tracts; sixth, isolated veins named as venous tracts; seventh, isolated bile ducts (BDs), named as biliary tracts; eighth, biliary–arteriolar tracts; ninth, pancreatic–biliary tracts (P-BT); tenth, pancreatic–venous tracts (P-VT). Macrophages aggregates are frequently associated with VBT and P-BT. The hepatic satellite cells (perisinusoidal cells) are observed in many species. The sinusoids are lined by endothelial and Kupffer cells (in some species). The biliary duct system is constituted of bile canaliculi, ductules, and BDs. Telocytes with their characteristics telopodes are located around the BDs. The pancreas of fish is a lobulated compound acinar gland, divided into exocrine and endocrine portions. Exocrine pancreatic tissues consist of scattered serous acini and is observed in two forms: first, disseminated in the spleen tissue, in mesentery around the intestine and intestinal bulb; and second, intrahepatically, around the branches of the portal vein. Two alveolar cell types are present in pancreatic acini: centroacinar cells and typical pyramidal acinar cells. Pancreatic stellate cells are demonstrated in the perivascular and 204the periacinar space of the pancreas. The acini show high lipase and alkaline phosphatase activity and moderate activity for acid phosphatase. The duct system is composed of the intralobular duct, interlobular pancreatic duct, and the main duct. The endocrine parts of the pancreas are organized as lightly staining Langerhan’s islets between exocrine acinar cells.
