Cutaneous O2 and CO2 exchanges in the dogfish, Scyliorhinus canicula

Total and cutaneous O2 and CO2 exchanges were studied in the unanesthetized, spinalectomized dogfish, Scyliorhinus canicula. Total oxygen uptake and carbon dioxide output were measured with an open flow respirometer. Cutaneous fluxes of O2 and CO2 were determined on the tail, confined in the posterior compartment of a two-chambered respirometer, in normoxic conditions but under three different values of the transcutaneous Pco2 difference. Oxygen consumption and CO2 production were measured on excised skin patches confined in known volumes of normoxic, normocapnic sea water. The cutaneous CO2 flux varied almost linearly with the transcutaneous Pco2 difference. In dogfish kept in normoxic, normocapnic sea water, extrabranchial exchanges of O2 and CO2 across the body surface amounted to less than 5% (O2) and 4% (CO2) of the total exchanges, and practically represented the intrinsic O2 consumption and CO2 production of the skin itself. Consequently, the net transcutaneous fluxes of O2 and CO2 can be considered as negligible in the normoxic, normocapnic dogfish. Transcutaneous CO2 losses do not explain low values of Paco2 and gill exchange ratios previously observed in hyperoxic dogfish.