Abstract
Background:
The rock goby, Gobius paganellus is not a commercial species. This species has an essential rule in the coastal ecosystem as a biological indicator. Therefore, it has been selected as study's model species.
Aim:
Due to the insufficient studies that have been described on the hepatopancreas of G. paganellus, this study aimed to provide information on the anatomical and histological structure of the hepatopancreas of the alimentary canal of this species in the western coast of Libya.
Methods:
Fifty mature G. paganellus specimens were collected from the northwest of Libya (Tajoura, Jodaem, and Farwa Island). Total length and total weight of the samples were measured, and performed by using gross anatomy, and histology. Then, the histological sections (3-5 µm) were stained with hematoxylin and eosin (H and E).
Results:
Morphologically, the liver has a large pyriform lobe. The dorsal surface of the liver is shiny and smooth, and the ventral surface contains shallow sulci; each sulus has a large blood vessel. Histologically, the liver is wrapped with a thin capsule of fibro-connective tissue. The hepatic parenchyma is made of hepatocytes with blood sinusoids. The hepatocytes are polygonal-shaped cells and have no hepatic lobules or portal triads. Melano-macrophage centers are distributed next to the blood vessels and bile ducts. The bile ducts are lined by columnar epithelial cells. The exocrine pancreatic tissue was observed in the liver parenchyma and it consists of acini that are composed of pyramidal cells and contain zymogen granules.
Conclusion:
The liver of this species has both pancreatic and liver tissue, which was discovered in this investigation for the first time.

Key words: G. paganellus, Hepatopancreas, Architecture, Libya