Editorial Type:
Article Category: Research Article
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Online Publication Date: Dec 01, 2000

Specialization of the Urinary Bladder in Two Pseudoplesiopines (Teleostei: Pseudochromidae)

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Page Range: 1083 – 1089
DOI: 10.1643/0045-8511(2000)000[1083:SOTUBI]2.0.CO;2
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Abstract

Two pseudoplesiopine species, Pseudoplesiops rosae and Pseudoplesiops howensis, were found to possess a highly specialized urinary bladder. The urinary bladder was so-identified by tracking the opisthonephric ducts from the trunk kidney to their termination within the bladder lumen. The specializations 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 bladder lumen were lined by a conspicuous tall columnar epithelium. The epithelium and septa were most prominent in fish having no or only small amounts of accumulated lumenal secretions. In other fish having large amounts of stored lumenal secretions, the septa and septal epithelia were reduced or absent, suggesting a holocrine form of secretion. The tall columnar epithelium in the bladder consisted of cells having granular cytoplasm and, in some instances, small amounts of contained material identical in appearance to the accumulated secretions occupying the bladder, suggesting that the epithelial cells may be the source of the secretions. Considerable amounts of stored secretions were present in approximately half of the specimens sampled from these two species. These secretions were resistant to digestion and clearing in counterstained skeletal preparations and were PAS-unreactive, suggesting the absence of a carbohydrate component. The composition and function of the secretions is currently unknown; however, the equal frequency of occurrence of secretions in immatures and adults of both sexes rules out a solely reproduction-associated function.

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Copyright: The American Society of Ichthyologists and Herpetologists
Fig. 1.
Fig. 1.

Pseudoplesiops rosae. (A) Two cleared-and-counterstained specimens (BMNH 1999.1.14.14–16) showing presence of an opaque, nonclearing structure in posterior portion of abdominal cavity in upper specimen 21.4 mm SL, and lower specimen 18.0 mm SL without opaque, nonclearing structure. Arrow points to posterior margin of urinary bladder. (B) Section through center of urinary bladder showing point of exit from body via urogenital pore (up). (C) Section showing median septum (ms), peripherally located septa (s) and centrally located duct (d) just prior to its open-ended terminus; dorsalmost point at upper left corner. (D) Section of bladder showing extensive septal partitioning and well-defined simple columnar epithelium (ce). (B–D) are transverse sections (7 µm thickness); bars represent 200 µm


Fig. 2.
Fig. 2.

Transverse sections (7 µm thickness) of Pseudoplesiops rosae. (A) Urinary bladder with few stored secretions showing extensive septal intrusions (s), reduced central lumen (l) and point of exit via urogenital duct (gd). (B) Section showing descent of paired ducts (pd) into urinary bladder from point of entry. (C) Section showing paired ducts (pd) at point of entry into urinary bladder and numerous vacuoles (v) within stored secretions, possibly reflecting lipid dropout. (D) Section showing continuation of paired ducts as opisthonephric ducts (od) extending from urinary bladder up toward kidney. Bars represent 100 µm; in (A) dorsalmost point is at upper right corner; in (D) dorsalmost point is at upper left corner


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Accepted: Apr 28, 2000