Active ureogenesis in a freshwater air‐breathing teleost, <i>Heteropneustes fossilis</i>

Abstract

Abstract Activities of all the enzymes of ornithine‐urea (o‐u) cycle and uricolytic pathway were assayed in different tissues of a freshwater air‐breathing teleost, Heteropneustes fossilis . High activity of all o‐u cycle enzymes as observed in the liver and kidney, were comparable to those of actively ureogenic fishes and amphibians. All the three enzymes of uricolytic pathway were found only in liver tissue. These observations strengthen an earlier suggestion made that active ureogenesis did exist in some freshwater teleosts such as H. fossilis . Presence of an active o‐u cycle in H. fossilis indicates that this fish is either relatively primitive to the purely aquatic freshwater teleosts retaining the ancestral character of a functional o‐u cycle or the genes for the synthesis of o‐u cycle enzymes might have been derepressed as a secondary modification for its adaptation to temporary dehydration or hyper‐ammonia environment.