Oxidative enzymes in the urinary apparatus of several marine fishes

The distribution and activities of several oxidative enzymes in the urinary apparatus of seven marine fish species (hagfish, lesser spotted dogfish, electric ray, herring, marine catfish, cod, sea-horse) have been studied. Species were selected from three main taxonomic groups: Cyclostomata, Elasmobranchii and Teleostei. Distinctly positive enzyme reactions were found in the tubular elements of the kidney and the collecting duct-archinephric duct system, with the exception of the generally weak staining intensities for NADP-linked malate dehydrogenase. In the proximal tubule segment the second, ore distal part (PII) reacted, in general, very strongly when compared with the first proximal part (PI). If present, the distal tubule in teleosts showed only weak reactions, while this segment in elasmobranchs exhibited moderate to strong enzyme activities. In the epithelial cells of the collecting tubule-collecting duct system stronger reactions were confined to the glomerular teleost species, the corresponding part of the elasmobranch kidney showing weak staining intensities. In the urinary duct system distinctly positive enzyme reactions were only to be found in the archinephric duct of the teleost species, except for Plotosus. The ureters of the elasmobranchs exhibited weak enzymes activities throughout. The enzyme patterns of the various types of urinary tubules and ducts are compared with observations from several morphological and physiological studies. The histochemical findings are discussed in relation to corresponding investigations of freshwater fishes and problems arising from phylogenetic divergence of marine fish groups.