Absence of regulated blood-oxygen transport in response to strenuous exercise by the shovelnosed ray, <i>Rhinobatos typus</i>

Abstract

Haematological indices and the erythrocyte nucleotides ATP and GTP remained unchanged following strenuous exercise. These data suggest that neither increased oxygen-carrying capacity nor modulated haemoglobin-oxygen affinity are available to assist oxygen debt recovery after exercise. Marked increases in plasma lactate pointed to a post-exercise metabolic acidosis. Concentrations of adrenaline and noradrenaline increased sharply after strenuous exercise, with adrenaline the dominant catecholamine. These endocrine responses were not coupled to plasma lactate, and did not result in erythrocyte swelling. The constancy of the plasma ions Na+ and Cl- suggests that branchial ion- exchange mechanisms remained patent, but a rise in K+ was consistent with leakage from the myotomal mass. These responses suggest that the ability of the rhinobatoid ray to resume aerobic activity following burst exercise is severely limited.