Circulation, oxygen transport, and activity in the crayfish.

Heart and ventilation frequencies, oxygen uptake rate, hemocyanin concentration, and pre- and postbranchial PO2 and pH were measured in unrestrained crayfish (Pacifastacus leniuculus) immediately following routine and forced (maximum) activity. Experiments were performed at 20 degrees C, the temperature of maximum scope for activity in this species, and at 10 and 25 degrees C. A procedure for using N-ethylmaleimide as an anticoagulant in hemolymph sampling is described. Hemocyanin oxygen saturation, oxygen content of pre- and postbranchial hemolymph, cardiac output, and stroke volume were estimated from the measured parameters. PO2 of postbranchial hemolymph sampled immediately after routine activity was low (9-12 Torr), accompanied by hemocyanin oxygen saturations of 55-75%. Maximum forced activity for 10 min caused further reduction in these values. Thus hemocyanin is apparently not usually saturated with oxygen in these crayfish. Cardiac output, as estimated by the Fick principle, was high (at 20 degrees C, 236 ml x kg-1 x min-1 for routine activity and 969 ml x kg-1 x min-1 for forced activity). Evidence is presented that ventilation, rather than circulation, limits active oxygen uptake and scope for activity both above and below 20 degrees C.