title: Active ammonia transport and excretory nitrogen metabolism in the climbing perch, Anabas testudineus, during 4 days of emersion or 10 minutes of forced exercise on land.
abstract: The climbing perch, Anabas testudineus, inhabits large rivers, canals, stagnant water bodies, swamps and estuaries, where it can be confronted with aerial exposure during the dry season. This study aimed to examine nitrogen excretion and metabolism in this fish during 4 days of emersion. Contrary to previous reports, A. testudineus does not possess a functional hepatic ornithineurea cycle because no carbamoyl phosphate synthetase I or III activity was detected in its liver. It was ammonotelic in water, and did not detoxify ammonia through increased urea synthesis during the 4 days of emersion. Unlike many air-breathing fishes reported elsewhere, A. testudineus could uniquely excrete ammonia during emersion at a rate similar to or higher than that of the immersed control. In spite of the fact that emersion had no significant effect on the daily ammonia excretion rate, tissue ammonia content increased significantly in the experimental fish. Thus, it can be concluded that 4 days of emersion caused an increase in ammonia production in A. testudineus, and probably because of this, a transient increase in the glutamine content in the brain occurred. Because there was a significant increase in the total essential free amino acid in the experimental fish after 2 days of emersion, it can be deduced that increased ammonia production during emersion was a result of increased amino acid catabolism and protein degradation. Our results provide evidence for the first time that A. testudineus was able to continually excrete ammonia in water containing 12 mmol l(-1) NH4Cl. During emersion, active ammonia excretion apparently occurred across the branchial and cutaneous surfaces, and ammonia concentrations in water samples collected from these surfaces increased to 20 mmol l(-1). It is probable that the capacities of air-breathing and active ammonia excretion facilitated the utilization of amino acids by A. testudineus as an energy source to support locomotor activity during emersion. As a result, it is capable of wandering long distance on land from one water body to another as reported in the literature.
authors.affiliation: Department Of Biological Science, National University Of Singapore, Kent Ridge, Singapore 117543, Republic Of Singapore.
authors.forename: Yi L
authors.initials: YL
authors.lastname: Tay
authors.forename: Ai M
authors.initials: AM
authors.lastname: Loong
authors.forename: Kum C
authors.initials: KC
authors.lastname: Hiong
authors.forename: Shi J
authors.initials: SJ
authors.lastname: Lee
authors.forename: Yvonne Y M
authors.initials: YY
authors.lastname: Tng
authors.forename: Nicklaus L J
authors.initials: NL
authors.lastname: Wee
authors.forename: Serene M L
authors.initials: SM
authors.lastname: Lee
authors.forename: Wai P
authors.initials: WP
authors.lastname: Wong
authors.forename: Shit F
authors.initials: SF
authors.lastname: Chew
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Wilson
authors.forename: Yuen K
authors.initials: YK
authors.lastname: Ip
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000641:Ammonia / Q000378:metabolism*; D025041:Animal Migration; D000818:Animals; D001693:Biological Transport, Active; D004734:Energy Metabolism; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D008099:Liver / Q000201:enzymology / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D009043:Motor Activity; D009584:Nitrogen / Q000378:metabolism*; D009952:Ornithine / Q000378:metabolism; D010101:Oxygen Consumption; D010471:Perches / Q000378:metabolism*; D014508:Urea / Q000378:metabolism
chemical_list: D000596:Amino Acids; D000641:Ammonia; D014508:Urea; D009952:Ornithine; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen