ABSTRACT
Arterial and mixed venous blood were sampled through chronically implanted cannulae from rested and swimming hagfish.
remained high when hagfish were swum for 15min at a velocity of 20cms-1. 
fell from 17-2mmHg at rest to 3’5 mmHg after swimming, and the arteriovenous pH difference increased from 0·15 to 0·25 pH units.Whole blood oxygen equilibrium curves were essentially hyperbolic (Hill’s n value = 1·38) and gave a half-saturation
(P50) value of 12·3 mmHg at pH 7·8 and 16°C. A CO2-Bohr factor (ϕ = ΔlogP50/ΔpH) of –0·43 and a limited buffering capacity of the blood, amounting to approx. 4slykes, were observed.The role of the blood in transporting oxygen and carbon dioxide both at rest and after swimming is established by in vivo blood gas measurements and in vitro oxygen-binding data. The low internal
at rest is close to the P50 measured under similar conditions and the hyperbolic equilibrium curve permits further oxygen unloading when 
falls during swimming.
