The pancreas is a gland of mixed secretion; in fish it lies in the loop between the stomach and intestine. In most fish, indistinguishable because it is fused with the liver. In addition to digestive enzymes secreted directly into the intestine - trypsin, lipase, amylase, maltase, breaking down proteins, fats and carbohydrates. The semi-pancreatic gland synthesizes insulin, secreted directly into the bloodstream.
In the pancreas of fish, as in higher animals, insulin is produced in the islets of Langerhans. In lampreys and bivalve fish, the pancreas is essentially hidden in the intestinal wall. In sturgeon and some bony fishes, as well as hagfish, the pancreas is lodged in the liver tissue. In most carp and perch, the pancreas together with the liver forms a single organ - hepatopancreas. In some fish pancreas is located near the gallbladder and its ducts, spleen. Pancreas secretes into the intestine of fish enzymes - proteases, lipases, amylase - providing digestion of proteins, fats and carbohydrates. Islet cells (endocrine cells) produce the hormone insulin, which regulates blood glucose levels.