Many intertidal teleosts exhibit amphibious behavior and facultatively breathe air. We examined the intertidal teleost Fundulus heteroclitus, the mummichog, for the ability to take up O2 and release CO2 aerially over a range of temperatures. Additionally, we measured aquatic oxygen consumption before and after aerial emergence. Fundulus heteroclitus exchanged O2 and CO2 effectively during an emergence of 1.5 h. Respiratory exchange ratios (RER, CO2 release: O2 uptake) were between 0.74 and 1.0, sufficient to keep pace with metabolic CO2 production. Oxygen consumption was significantly lower in air than in water. Upon return to water after an hour of aerial emergence, aquatic O2 consumption was no higher than prior to emergence, an indication that anaerobic metabolism is not used during air emergence. We conclude that F. heteroclitus can withstand air emergence in the salt marsh by breathing air. Emergence and aerial respiration might appear to be a specific adaptations to survival in intertidal habitats in F. heteroclitus, but phylogenetic evidence suggests that these traits may also be ancestral characters. Additional physiological testing in closely related species will aid in elucidating the evolution and adaptive characteristics of aerial respiration in this clade.