Abstract Some metabolic fuels in hemolymph samples from the sinuses at the base of the third walking leg (pre-branchial blood) and from the cardiac sinus (post-branchial blood) in the red lobster, Panulirus interruptus, were evaluated during normoxia, hypoxia, and at the critical oxygen point ( P cr) at two temperatures of acclimatization. Three-way ANOVA indicated a significant effect of oxygen saturation R(6140)=19.84 in metabolic fuel concentrations. Lactate varied from 0.01 to 0.29 mg/ml at 20 °C, from 0.02 to 0.29 mg/ml at 27 °C, and increased significantly during hypoxia ( P<0.05). Glucose varied from 0.10 to 0.27 mg/ml at 20 °C, from 0.13 to 0.33 mg/ml at 27 °C, and increased with temperature. Proteins varied from 80.78 to 119.99 mg/ml at 20 °C and from 82.99 to 130.30 mg/ml at 27 °C.