Specialization of the urinary bladder in two pseudoplesiopines (Teleostei : Pseudochromidae)

Two pseudoplesiopine species, Pseudopleisops rosae and Pseudoplesiops howen sis, were found to possess a highly specialized urinary bladder. The urinar y bladder was so-identified by tracking the opisthonephric ducts from the t runk kidney to their termination within the bladder lumen. The specializati ons included a pronounced thickening of the bladder wall, an elaboration of the internal surface area by means of extensive septal intrusions, and the frequent presence of vesicular or colloidal secretions within the bladder lumen. The extensive septal intrusions as well as the inner wall of the bla dder lumen were lined by a conspicuous tall columnar epithelium. The epithe lium and septa were most prominent in fish having no or only small amounts of accumulated lumenal secretions. In other fish having large amounts of st ored lumenal secretions, the septa and septal epithelia were reduced or abs ent, suggesting a holocrine form of secretion. The tall columnar epithelium in the bladder consisted of cells having granular cytoplasm and, in some i nstances, small amounts of contained material identical in appearance to th e accumulated secretions occupying the bladder, suggesting that the epithel ial cells may be the source of the secretions. Considerable amounts of stor ed secretions were present in approximately half of the specimens sampled f rom these two species. These secretions were resistant to digestion and cle aring in counterstained skeletal preparations and were PAS-unreactive, sugg esting the absence of a carbohydrate component. The composition and functio n of the secretions is currently unknown; however, the equal frequency of o ccurrence of secretions in immatures and adults of both sexes rules out a s olely reproduction-associated function.