Abstract Silver trevally ( Pseudocaranx dentex) are highly athletic marine teleosts inhabiting the tropical waters of the Great Barrier Reef, Australia. Burst swimming increased plasma lactate from 1.6 ± 0.4 S.D. to 21.6 ± 3.3 mM ( N = 6), among the highest values reported for functional hypoxia in fish. These data support the hypothesis that elite swimmers release lactate produced in the myotome into the circulation following anaerobic burst activity. The fish further developed a hyperglycaemic response to burst exercise with plasma glucose increasing from 6.6 ± 2.0 to 13.2 ± 2.3 mM ( N = 6). Post-exercise erythrocyte swelling also occurred, but nucleoside triphosphate levels remained unaltered and do not provide a mechanism to modulate haemoglobin function during exercise. Metabolism of the blood cells appeared to be fuelled by both lactate and glucose.