|
| |
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
Accumulation of ammonia in the body and NH3 volatilization from alkaline regions of the body surface during ammonia loading and exposure to air in the weather loach Misgurnus anguillicaudatus
1 Department of Biological Sciences, National University of Singapore, 10 Kent Ridge Road, Singapore 117543, Republic of Singapore,
2 Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China,
3 Department of Natural Sciences, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616, Republic of Singapore and
4 Centro Interdisciplinar de Investigacao Marinha e Ambiental-CIIMAR, Rua do Campo Alegre 823, 4150-180 Porto, Portugal
*Author for correspondence (e-mail: bhrand{at}cityu.edu.hk)
Accepted 18 December 2001
The weather loach Misgurnus anguillicaudatus inhabits rice fields that experience drought in summer and ammonia loading during agricultural fertilisation. Exposure of specimens to ammonia led to the accumulation of ammonia in muscle, liver and blood. The level of ammonia reached in the plasma was the highest reported among fishes. Ammonia was not detoxified to urea, and urea excretion rate was unaffected by ammonia exposure. Fish acidified the water to reduce ammonia loading. Ammonia loading, unlike aerial exposure, did not induce glutamine synthesis, and there was no accumulation of glutamine. This is a unique observation different from those reported for other fishes in the literature. An initial switch to partial amino acid catabolism led to the accumulation of alanine and was probably associated with a decreased rate of ammonia production. Aerial exposure led to decreases in rates of ammonia and urea excretion, as well as the accumulation of tissue ammonia. As the internal ammonia levels increased, M. anguillicaudatus was able to excrete some ammonia in the gaseous form (NH3). The percentage of ammonia excreted as NH3 increased with time of exposure and with increasing temperature. It appears that air-breathing through the gut is involved, with the anterior portion of the digestive tract playing a central role: it became significantly more alkaline in fish exposed to air or to environmental ammonia. The skin, which also became more alkaline during air exposure, may also be involved in ammonia volatilization in air-exposed fish. This represents the first report of a fish using volatilization of NH3 as part of a defence against ammonia toxicity. It can be concluded that the main strategy adopted by M. anguillicaudatus confronted with ammonia loading or air exposure is to tolerate high ammonia levels in the tissues. During periods of elevated tissue ammonia levels, some ammonia is lost by volatilization via air-breathing using the gut. In addition, some ammonia may be lost across the skin during air exposure.
Key words: ammonia, ammonia loading, urea, air exposure, volatilization, weather loach, Misgurnus anguillicaudatus.
This article has been cited by other articles:
|
|
 |
|
  S. L. Litwiller, M. J. O'Donnell, and P. A. Wright Rapid increase in the partial pressure of NH3 on the cutaneous surface of air-exposed mangrove killifish, Rivulus marmoratus J. Exp. Biol., May 1, 2006; 209(9): 1737 - 1745. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. K. Ip, M. W. F. Leong, M. Y. Sim, G. S. Goh, W. P. Wong, and S. F. Chew Chronic and acute ammonia toxicity in mudskippers, Periophthalmodon schlosseri and Boleophthalmus boddaerti: brain ammonia and glutamine contents, and effects of methionine sulfoximine and MK801 J. Exp. Biol., May 15, 2005; 208(10): 1993 - 2004. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. K. N. Tsui, D. J. Randall, L. Hanson, A. P. Farrell, S. F. Chew, and Y. K. Ip Dogmas and controversies in the handling of nitrogenous wastes: Ammonia tolerance in the oriental weatherloach Misgurnus anguillicaudatus J. Exp. Biol., May 15, 2004; 207(12): 1977 - 1983. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. S. L. Tay, S. F. Chew, and Y. K. Ip The swamp eel Monopterus albus reduces endogenous ammonia production and detoxifies ammonia to glutamine during 144 h of aerial exposure J. Exp. Biol., July 15, 2003; 206(14): 2473 - 2486. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. F. Chew, M. Y. Wong, W. L. Tam, and Y. K. Ip The snakehead Channa asiatica accumulates alanine during aerial exposure, but is incapable of sustaining locomotory activities on land through partial amino acid catabolism J. Exp. Biol., February 15, 2003; 206(4): 693 - 704. [Abstract] [Full Text] [PDF]
|
|
