Nitrogen metabolism and excretion in the mangrove killifish Rivulus marmoratus II. Significant ammonia volatilization in a teleost during air-exposure.
The mangrove killifish Rivulus marmoratus can tolerate prolonged periods of air-exposure (>1 month). During these periods of emersion, we hypothesized that R. marmoratus would convert potentially toxic ammonia into urea and free amino acids (FAAs). In air-exposed fish, both ammonia (J(Amm)) and urea (J(Urea)) excretion continued at approximately 57 % and 39 %, respectively, of submerged rates. Remarkably, approximately 42 % of the total ammonia excreted during air-exposure was through NH(3) volatilization. Ammonia did not accumulate in whole-body tissues of air-exposed fish, but levels of both urea and some FAAs (primarily alanine and glutamine) were up to twofold higher after 10 days. The activities of the ornithine-urea cycle enzymes carbamoyl phosphate synthetase III and ornithine transcarbamylase increased (by approximately 30 % and 36 %, respectively) in whole-body tissues of air-exposed fish, while levels of arginase remained unchanged. The activities of enzymes involved in amino acid and oxidative metabolism were not significantly different between control and air-exposed fish. Partitioning of the anterior and posterior ends of immersed fish revealed that just over half (57 %) of the total nitrogen (ammonia+urea) was excreted through the anterior end of the fish, presumably via the branchial tissues, while emersed fish increased excretion via the posterior end (kidney+skin). R. marmoratus do not undergo a shift towards ureotelism during air-exposure. Rather, we propose that R. marmoratus are able to survive on land for extended periods without significant ammonia accumulation because they continuously release ammonia, partially by NH(3) volatilization.
Frick
N T
NT
Department of Zoology, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
Wright
P A
PA
D000388:Air; D000596:Amino Acids / Q000378:metabolism; D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D001119:Arginase / Q000378:metabolism; D019731:Carbon-Nitrogen Ligases / Q000378:metabolism; D023781:Fundulidae / Q000378:metabolism*; D005880:Gills / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D009952:Ornithine / Q000378:metabolism; D009954:Ornithine Carbamoyltransferase / Q000378:metabolism; D014508:Urea / Q000378:metabolism; D014835:Volatilization
D000596:Amino Acids; D005973:Glutamine; D018698:Glutamic Acid; D000641:Ammonia; D014508:Urea; D009952:Ornithine; D009954:Ornithine Carbamoyltransferase; D001119:Arginase; D019731:Carbon-Nitrogen Ligases; C024233:carbamoyl-phosphate synthetase (N-acetylglutamate); D009584:Nitrogen