Abstract: Objective To research on the intrahepatic biliary system in the zebrafish, Brachydanio rerio. Methods By using enzyme histochemical characterization, immunohistochemistry and electron microscopy. Results The biliary system was arranged in arborization in the parenchyma.The biliary tree included sequentially by intracellular and intercellular canaliculi，preductules,ductules and ducts.The intercellular originated at the neighborhood of the nucleus to extend to the cell surface where it emptied into the intra parenchymal biliary passage running in the interhepatocytic space. In the preductules，the wall was formed by bile preductular epithelial cells and hepatocytes .The bile preductular epithelial cells were linked to hepatocytes by the tight junctions. The wall of the biliary ductule usually consisted integrally 2 to 4 biliary epithelial cells. These cells had no basal lamina and were contacted with hepato-cytes directly. A ductule that was composed of a single cell and was embedded between two adjoining liver cells was found by TEM. The lumen of this ductule was very narrow and formed by the infolding of the plasma membrane of the ductule cell. The wall of bile ducts was composed of cuboidal epithelial cells, and the bile duct was encircled by the connective tissue. Whereas in ducts, apart from those cells，there were intraepithelial lymphocytes.This suggested that there exited mucosal immune response. The preducules and ductules formed a segment connecting canaliculi to ducts, thus, we considered that segment as being analogous to the mammalian canals of Hering.The reactions for Mg²⁺-dependent ATPase showed that bile tree was strained brownish-black color and interwove into a network. The bile system was revealed by immunstaining with a monoclonal antibody 2F11 that detected biliary epithelial cell bodies which are distributed scattcrcdly in interhepatocytic and the proximal regions of the ducts arising from these cells was stained. Conclusions The bile systerm in zebtafish is not only different with the mammals and birds, but also with other bony fish.

Key words: Zebrafish, Liver, Bile system