Arginase-Mediated Ureogenesis as an Adaptive Response to Water Restriction in Heteropneustes fossilis

It is well-known that fishes excrete ammonia as their major nitrogenous waste product. However, if they are kept in a water-restricted condition for a certain period of time, they may switch over to urea excretion. In the present study, it was tried to ascertain if in Heteropneustes fossilis (Shingi fish) ureogenesis is of any importance which may avoid any deposition of toxic ammonia during water-restricted condition. For the experiment, hundred fishes were collected and used. Urea and ammonia, excreted in the water of the aquarium, are estimated and the activity of arginase was measured in the hepatic tissue for three (03) months. During the experimental period of three (03) months, in Heteropneustes fossilis the excretory ammonia was found to be decreasing as compared to the excretory urea which showed a gradual increase during the experimental period. In Heteropneustes fossilis, a high degree of correlation is observed between excretory ammonia and urea with r (coefficient of correlation) above 0.9. However, the correlation between the activity of arginase and excretory ammonia and urea is found as moderate. The present work signifies that even if Heteropneustes fossilis faces water scarcity, it can change its metabolism and thus this does not impact the culture of this fish.