Gill morphology of the mangrove killifish (Kryptolebias marmoratus) is plastic and changes in response to terrestrial air exposure.
Many fishes in the marine intertidal zone have the ability to exchange respiratory gases in air during brief periods out of water. Previous studies on marine amphibious fishes such as mudskippers and rockskippers have shown that they release CO2 in air at a rate consistent with its release in aquatic respiration. Respiratory Exchange Ratios (RER, CO2 released per O2 consumed) are between 0.7 and 1.0, similar to Respiratory Quotients (CO2 produced metabolically per O2 consumed). However, previous studies of temperate intertidal fishes emerged only at low tides have been less consistent, with two species reported similar in ability to the amphibious skipper fishes, and two others reported with much lower RERs in air. This study examines 12 species of fishes, from six families (Batrachoididae, Cottidae, Gobiesocidae, Kyphosidae, Pholididae, and Stichaeidae), present in the intertidal zone of California. All 12 species exchanged O2 and CO2 in air. Like the amphibious skipper fishes of marine tropical waters, many intertidal fishes of the temperate zone release CO2 during low tide emergence in quantities sufficient to match its metabolic production. These results indicate that CO2 release is not hampered by the change in respiratory medium from water to air.