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

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 NH(3) volatilization; however, the sites and mechanisms are unclear. We hypothesized that the cutaneous surface is an important site of NH(3) volatilization in air-exposed R. marmoratus. Ion-selective microelectrodes were used to measure the NH(4)(+) 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 approximately 18-fold increase in the NH(4)(+) 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(NH(3))) was 608-1,251 microTorr, representing a 33- to 75-fold increase over control (immersed) fish. The P(NH(3)) on the cutaneous surface water film was more than sufficient to account for the rate of NH(3) volatilization under terrestrial conditions. Together, these data indicate that during air exposure, R. marmoratus utilize the cutaneous surface as a key site of NH(3) volatilization.