A histomorphological comparison of the urinary systems in the Serranid fishes, Roccus sexatilis (Walbaum) and Roccus americanus (Gmelin)

The urinary systems of Roccus saxatilis (Walbaum) and Roccus ~­ icanus (Gmelin) were studied to check the validity of the monogeneric classification and to examine the osmoregulatory mechanism that allows the species to survive in environments of various salinities. The gross anatomy of the urinary systems of 13 ~· saxatilis and 12 !!o americanus showed a number of similarities to exist, e.g. the general mesonephric form and si7.e, uretal position and length, and the renal venous system. The head kidney, a hemopoietic organ, was larger in E· ~­ atilis than in !!· americanus. Histolorical comparisons were made of H and E serial sections 0f the posterior part of the kidneys, and of the ureter, from three !!· sa.xatilis and four ~· americanus; included were the entire kidneys of two 2-year-old males of each specieso The kidney of a young specimen of each species was also studied. The ~lomeruli in E· americanus were found to be larger than those iri ~· sa.xatilis; however, in a previous study, freshwater ,!!o saxatilis were shown to have glomeruli of intermediate size. 'l'he number of poblet cells in the anterior part of the ureter was greater in g. saxatilis and may be correlated with glomerular size. A distal tubular segment, usually present in freshwater fishes, was absent in both species; probably a reflection of their marine origin. As the differences in the urinary system were explained on the basis of selective adaptation, they, and the number of similarities, were considered to support a m0no~eneric classification.