These fish are the only known self-fertilizing vertebrate hermaphrodite( Harrington, 1961), although there are true males and therefore sexual reproduction occurs in some natural populations ( Mackiewicz et al.,2006). The mangrove killifish, Kryptolebias marmoratus, lives in tropical mangrove forests in Florida, the Caribbean, Central and South America. marmoratus to thrive in both aquatic and terrestrial habitats. Furthermore, over a similar time frame, changes in V̇ CO 2 indicate that metabolic rate is maintained at a rate comparable to that of fish in water, underlying the remarkable ability of K. marmoratus remodel their gill structures in response to air exposure and that these changes are completely reversible. In contrast to V̇ O 2 in water, V̇ CO 2 in air showed no diurnal rhythm over a 24 h period. V̇ CO 2 varied between 6 and 10 μmol g –1 h –1 and was significantly higher on days 3, 4 and 5 relative to days 1 and 2. In the second experiment, V̇ CO 2 was measured in fish continuously over a 5-day period in air and compared with previous measurements of oxygen uptake( V̇ O 2) in water. Following 1 week of recovery in water, the ILCM regressed and gill lamellae were similar to control fish, indicating that the morphological changes were reversible. Morphometric analysis of light micrographs revealed that there were significant changes in the height of the ILCM, but there were no significant differences in lamellae width and length between any of the treatments. Following 1 week of air exposure, SEM indicated that there was a decrease in lamellar surface area. Scanning electron micrographs (SEM) and light micrographs of gill sections were taken, and morphometric analyses of lamellar width, lamellar length and interlamellar cell mass (ILCM) height were performed.

marmoratus were exposed to either water (control) or air for 1 h, 1 day,1 week, or 1 week followed by a return to water for 1 week (recovery).

During air exposure, when gills are no longer functional, we predicted that gill surface area would decrease. We tested the hypothesis that gill structure is plastic and that metabolic rate is maintained in response to air exposure. Amphibious mangrove killifish, Kryptolebias marmoratus (formerly Rivulus marmoratus), are frequently exposed to aerial conditions in their natural environment.

Terrestrial air navigation test