Ventilation, heart rate and respiratory gas exchange in the crayfish Austropotamobius pallipes (Lereboullet) submerged in normoxic water and following 3 h exposure in air at 15°C

1. Adult male and female freshwater crayfish, acclimated to 15°C, were observed to migrate from hypoxic water into air at a mean {Mathematical expression} of 42 mm Hg. 2. The rates of recovery after initial disturbance of heart rate (f_card), ventilation rate (f_resp), oxygen consumption {Mathematical expression} and ventilation volume V_W were followed for 18 h. Settled values were established after 3-5 h of submersion in normoxic water at 15°C. 3. On exposure to air at 15°C (R.H. 70-80%) for 3 h, f_card, f_resp and {Mathematical expression} were similar to settled submerged values. Ventilation volume in air V_air was only 5% of normoxic V_W. 4. In air the crayfish experienced internal hypoxia with postbranchial oxygen tension ( {Mathematical expression}) reduced to 33% and oxygen content ( {Mathematical expression}) to 45% of the submerged normoxic level. {Mathematical expression} was maintained by drawing on a venous reserve of oxygen, reducing postbranchial oxygen content ( {Mathematical expression}) in air to 15% of the submerged normoxic level. 5. After 3 h in air the crayfish experienced a marked acidosis of the haemolymph which was both respiratory, due to the accumulation of CO₂ and metabolic, due to the accumulation of lactate. 6. On return to water after 3 h in air, f_card, f_resp, {Mathematical expression} and V_W quickly returned to their settled normoxic values. There was evidence of an initial period of hyperventilation, but no repayment of an oxygen debt. 7. The effectiveness of respiratory gas exchange in water and in air are compared with other aquatic and terrestrial species.