Bimodal respiration in the intertidal fish,Xiphister atropurpureus(Kittlitz)†

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Abstract
The capacity of black pricklebacks (X. atropurpureus) for bimodal gas exchange was examined. Field observations revealed that these fish survived exposure to air for at least 6 h. Apparently, they use their skin or buccal cavity for gas exchange in air; pricklebacks lack a swim bladder or gill structures modified for that purpose. Pricklebacks maintained rates of O2 uptake during exposure to air in the laboratory which were equal to or even surpassed those in water. CO2 excretion was reduced significantly during air exposure. Carbonic anhydrase and acetazolamide, a specific inhibitor of carbonic anhydrase, were injected in these fish. Data suggested that CO2 excretion in air was limited by the uncatalyzed velocity of the plasma HCO3 dehydration reaction. This result is inexplicable in terms of the current understanding of piscine gas transfer.