Dosidicus gigas is a large, metabolically active, epipelagic squid known to undertake diel vertical migrations across a large temperature and oxygen gradient in the Eastern Pacific. Hypoxia is known to cause metabolic suppression in D. gigas. However, the precise oxygen level at which metabolic suppression sets in is unknown. Here we describe a novel ship-board swim tunnel respirometer that was used to measure metabolic rates and critical oxygen partial pressures (Pcrit) for adult squids (2–7 kg). Metabolic rate measurements were validated by comparison to the activity of the Krebs cycle enzyme, citrate synthase, in mantle muscle tissue (2–17 kg). We recorded a mean routine metabolic rate of 5.91 μmol g−1 h−1 at 10 °C and 12.62 μmol g−1 h−1 at 20 °C. A temperature coefficient, Q10, of 2.1 was calculated. D. gigas had Pcrits of 1.6 and 3.8 kPa at 10 and 20 °C, respectively. Oxygen consumption rate (MO2) varied with body mass (M) according to MO2=11.57 M−0.12±0.03 at 10 °C. Citrate synthase activity varied with body mass according to Y=9.32 M−0.19±0.02.