Development of the islets, exocrine pancreas, and related ducts in the Nile tilapia, Oreochromis niloticus (Pisces: Cichlidae)

Abstract

Pancreatic development and the relationship of the islets with the pancreatic, hepatic, and bile ducts were studied in the Nile tilapia, Oreochromis niloticus, from hatching to the onset of maturity at 7 months. The number of islets formed during development was counted, using either serial sections or dithizone staining of isolated islets. There was a general increase in islet number with both age and size. Tilapia housed in individual tanks grew more quickly and had more islets than siblings of the same age left in crowded conditions. The pancreas is a compact organ in early development, and at 1 day posthatch (dph) a single principal islet, positive for all hormones tested (insulin, SST-14, SST-28, glucagon, and PYY), is partially surrounded by exocrine pancreas. However, the exocrine pancreas becomes more disseminated in older fish, following blood vessels along the mesenteries and entering the liver to form a hepatopancreas. The epithelium of the pancreatic duct system from the intercalated ducts to the main duct entering the duodenum was positive for glucagon and SST-14 in 8 and 16 dph tilapia. Individual insulin-immunopositive cells were found in one specimen. At this early stage in development, therefore, the pancreatic duct epithelial cells appear to be pluripotent and may give rise to the small islets found near the pancreatic ducts in 16-37 dph tilapia. Glucagon, SST-14, and some PPY-positive enteroendocrine cells were present in the intestine of the 8 dph larva and in the first part of the intestine of the 16 dph juvenile. Glucagon and SST-14-positive inclusions were found in the apical cytoplasm of the mid-gut epithelium of the 16 dph tilapia. These hormones may have been absorbed from the gut lumen, since they are produced in both the pancreatic ducts and the enteroendocrine cells. At least three hepatic ducts join the cystic duct to form the bile duct, which runs alongside the pancreatic duct to the duodenum.

Notch-responsive cells initiate the secondary transition in larval zebrafish pancreas

“…The secondary islets maintain this position in adults (Fig. 1C), an observation also made in other teleosts (Morrison et al, 2004). At high magnification it can be seen that these secondary islets are in direct contact with branch points along the main duct (Fig.…”

Particle size and traffic of phagocytes between the turbot peritoneal cavity and lymphoid organs

“…We show that peritoneal cells containing macromolecules or phagocytosed beads became attached to the peritoneal folds that connect the visceral organs. These folds, which are surrounded by the visceral mesothelium, contain blood vessels, connective tissue and pancreas, as also described in other teleost fish species [33]. Phagocytes containing beads were found attached to the mesothelium, but also in regions of connective tissue that surround small vessels, which are located among the pancreatic acini, indicating migration of cells from the mesothelial surface to those vessels.…”

The Ultrastructure of Secretory Cells of the Islets of Langerhans in South American Catfish Rhamdia quelen

“…In actively feeding fish, they contain large numbers of bright eosinophilic, secretory granules. The endocrine pancreatic islet of Langerhans could be distinguished, and tissue encompasses -cells (producing glucagon-like peptide), -cells (producing insulin), and dcells (producing somatostatin) [3]. In mammals and humans most of the earlier electron microscopic descriptions of adult human pancreatic islets have been brief and minor portions of publications are primarily devoted to descriptions ofcell tumors or survey articles discussing the comparative morphology of the islets of several species [4].…”