Aerial release of CO2 and respiratory exchange ratio in intertidal fishes out of water

Synopsis 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.