ONTOGENY OF THE BILIARY-TRACT IN A TELEOST, THE SEA BASS DICENTRARCHUS-LABRAX L

Ontogenesis of the biliary tract in the sea bass Dicentrarchus labrax was studied using transmission electron microscopy from hatching to 3 months of age. The biliary intrahepatic network and extrahepatic ducts develop during primordial liver differentiation. When hepatoblasts fo rm groups and polarise, they create bile canaliculi at their apical po le. The main characteristic of these bile canaliculi is that they are roughly spherical. The biliary epithelial cells first appear just befo re mouth opening in prelarvae (day 5 after hatching). They constitute not only composite canaliculi with hepatocytes, but also cholangioles. Biliary ductules and ducts are visible from day 10 onward. During ont ogenesis, the primordial liver separates from the wall of the gut but remains connected to it by a cell cord. This cell cord becomes tubular , with an axial cavity dilating at the other end and giving successive ly the choledoc duct, cystic duct, and gall bladder.