Effects of salinity stress, ammonia exposure and feeding on excretory nitrogen metabolism in the marble goby, oxyeleotris marmorata
This study examined the effects of seawater acclimation, exposure to ammonia in freshwater or seawater or feeding on the marble goby, Oxyeleotris marmorata. O. marmorata exhibited hyperosmotic hyperionic regulation in freshwater, but undergo hypoosmotic hypoionic regulation during seawater exposure. Short-term seawater exposure resulted in cell volume regulation partially achieved by using FAAs as osmolytes. Long-term seawater exposure resulted in increase in sodium-potassium-ATPase activities in the gills and intestine. Glutamine accumulated in tissues of fish exposed to ammonia in freshwater or seawater, but increased glutamine synthesis through GS could have occurred outside the liver. Feeding led to a significant increase in GDH activities from the intestine and liver and the major amino acid accumulated was glutamate. Cloning and sequencing of GS in the liver eliminates the possibility of multiple splice variants or the products of multiple genes, suggesting the covalent modification of hepatic GS in response to various experimental conditions.
salinity, ammonia, feeding, nitrogen metabolism, marble goby, Oxyeleotris marmorata
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