Options
Nitrogen metabolism in the snakehead, Channa asiatica, during ammonia exposure
Author
Gan, Jumi
Supervisor
Chew, Shit Fun
Abstract
This study aimed at determining the tolerance of the snakehead, Channa asiatica, to environmental ammonia and at elucidating the strategies that it adopts to defend against ammonia toxicity during ammonia loading. In the laboratory, C. asiatica exhibited tolerance for ammonia loading of 50 mmol 1-1 and 100 mmol 1-1 for 48 h. The high tolerance of C. asiatica to ammonia exposure was attributed partially to its high tolerance to ammonia at the cellular and subcellular levels. During 48 h of exposure to 100 mmol 1-1 NH4Cl at pH 7.0, the ammonia contents in the muscle, liver, intestine and plasma of C. asiatica reached 11.9, 14.2, 9.33 and 2.98 μmol g-1, respectively. Similar to many tropical fishes, C. asiatica did not detoxify ammonia to urea during ammonia loading as urea synthesis is energy expensive. Instead, it resorts to partial catabolism of amino acids leading to the production of alanine in its muscle as alanine level increased 5.6-fold from 1.72 to 9.67 μmol g-1 in the muscle after C. asiatica was exposed to 100 mmol l-1 NH4Cl for 48 h. Also, the exogenous ammonia was detoxified to glutamine since glutamine synthetase (GS) activity increased significantly in the muscle. On the other hand, the increase in GS activity in the liver cum the increase in the relative protein abundance of hepatic GS and glutamate dehydrogenase in C. asiatica exposed to 100 mmol l-1 NH4Cl for 48 h indicated that the fish detoxifies the exogenous ammonia to glutamate and then to glutamine. A decrease in the total free amino acids in the plasma may indicate that a reduction in proteolysis and/or amino acid catabolism must have occurred to prevent ammonia toxicity. Thus, results in this study showed that C. asiatica resorts to different strategies in different tissues to alleviate ammonia toxicity when confronted with ammonia loading.
Date Issued
2012
Call Number
QL638.C486 Gan
Date Submitted
2012