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Functional ureogenesis in the gobiid fish Mugilogobius abei
K Iwata1, M Kajimura, T Sakamoto
1Biological Laboratory, Faculty of Education, Wakayama University, Wakayama 640-8510, Japan. katsuiw@center.wakayama-u.ac.jp
The Journal of Experimental Biology
|November 15, 2000
Summary
Gobiid fish Mugilogobius abei shift from ammonia to urea excretion when exposed to high ammonia levels. This ureogenesis occurs via the ornithine-urea cycle in non-hepatic tissues, aiding ammonia detoxification.
Area of Science:
- Biochemistry
- Environmental Toxicology
- Fish Physiology
Background:
- Ammonia is a toxic metabolic waste product.
- Ureogenesis is the process of urea synthesis.
- Fish typically excrete ammonia (ammonotely).
Purpose of the Study:
- To investigate the transition to ureogenesis in the gobiid fish Mugilogobius abei.
- To understand the mechanism of urea production under ammonia-loading conditions.
Main Methods:
- Fish were immersed in ammonia solutions, including (15)N-labelled ammonia.
- Urea and ammonia excretion rates were measured.
- (15)N-enrichment in tissues and excreta was analyzed.
- Enzyme activities and gene expression (CPSase III, O-UC enzymes) were assessed.
Main Results:
- Urea excretion increased sevenfold and represented 62% of total nitrogen excretion.
- (15)N incorporation confirmed urea synthesis from ammonia via glutamine.
- Glutamine synthetase activity and glutamine levels increased significantly.
- Ornithine-urea cycle enzymes were active in muscle, skin, and gill, but not significantly in the liver.
Conclusions:
- Mugilogobius abei transitions from ammonotely to ureotely under ammonia stress.
- Urea production primarily occurs through the ornithine-urea cycle in non-hepatic tissues.
- This highlights a multi-tissue detoxification strategy for ammonia in fish.