Acid‐base, fluid and electrolyte metabolism in the elasmobranch. III. oxygen, CO 2 , bicarbonate and lactate exchange across the gill

Methods have been developed which permit measurements of cardiac output and sampling of mixed venous and arterial blood in the elasmobrach, Squalus acanthias . These methods have been utilized to characterize some of the parameters involved in gill gas exchange. A total of 17 animals have been studied with the following results. Cardiac output: 1.49±0.57 1/kg/hr.; V̇ o 2 : 38.3±22.1 ml/kg/hr.; V̇ co2 : 32.1±19.0 ml/kg/hr.; RER: 0.92±0.17; PaO 2 : 104±27 mmHg; Pv̄ o 2 : 18±8.8 mmHg; PaCO 2 : 2.9±0.75 mmHg; Pv̄ co 2 : 4.6±1.1 mmHg; CaO 2 : 3.8±0.75 vol. %; Cv̄ o 2 : 1.26±0.59 vol. %; pHa: 7.52±0.10 units; Pv̄: 7.42±0.11 units; [HCO 3 −] a : 3.92± 1.14 meq/1; [HCO 3 −]v̄: 4.80±1.15 meq/1; [dissolved CO 2 ] a : 0.17± 0.04 mM/1; [dissolved CO 2 ]v̄: 0.24±0.04 mM/1; [lactate−] a : 13.47±7.17 meq/1; [Lactate−]v̄: 13.01±8.18 meq/1. Some of the mechanisms involved in gill gas exchange have been characterized.