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First published online April 18, 2006
Journal of Experimental Biology 209, 1737-1745 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02197

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Rapid increase in the partial pressure of NH₃ on the cutaneous surface of air-exposed mangrove killifish, Rivulus marmoratus

S. L. Litwiller¹, M. J. O'Donnell² and P. A. Wright^1,*

¹ Department of Integrative Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
² Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada

^* Author for correspondence (e-mail: patwrigh{at}uoguelph.ca)

Accepted 7 March 2006

Mangrove killifish, Rivulus marmoratus, are tolerant of prolonged periods of air exposure (>30 days). Air-exposed R. marmoratus eliminate more than 40% of their total ammonia through NH₃ volatilization; however, the sites and mechanisms are unclear. We hypothesized that the cutaneous surface is an important site of NH₃ volatilization in air-exposed R. marmoratus. Ion-selective microelectrodes were used to measure the NH₄⁺ concentration and pH in the boundary layer on the cutaneous surface of fish in water or air (acute: 1 h, chronic: 11 days). Following acute and chronic air exposure, there was a 18-fold increase in the NH₄⁺ concentration and a 0.3–0.6 pH unit increase on the cutaneous surface of R. marmoratus. In air-exposed fish, the calculated cutaneous partial pressure (P_NH3) was 608–1251 µTorr, representing a 33- to 75-fold increase over control (immersed) fish. The P_NH3 on the cutaneous surface water film was more than sufficient to account for the rate of NH₃ volatilization under terrestrial conditions. Together, these data indicate that during air exposure, R. marmoratus utilize the cutaneous surface as a key site of NH₃ volatilization.

Key words: NH₃ volatilization, nitrogen excretion, ammonia excretion, water pH, fish skin, boundary layer, amphibious fish, Rivulus marmoratus

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