The fish gallbladder, like the mammalian one, is an accessory organ of the digestive system that stores and secretes concentrated bile. This bile has several functions, such as facilitating several digestive functions, eliminating conjugated metabolites in the liver, and participating in the enterohepatic bile circulation. The dietary demands and adaptive strategy of quality of bile production are probably reflected in the ultrastructural diversity of these accessory organs of the digestive system. Most of the textbooks treating the topic of the fish digestive system lack the elementary histology and ultrastructure of the gallbladder and the associated biliary tract. Descriptions in literature of the biliary tracts of fish reveal some confusion regarding the nomenclature to be used in describing the morphology of the elements of the biliary system from its proximal region to its distal region. The successive layers found in mammalian gallbladders can be differentiated in fish using light (LM) and electron microscopy (TEM).