CIRCULATORY AND RESPIRATORY EFFECTS OF AN HYPOXIC STRESS IN THE SIBERIAN STURGEON

Changes in circulatory, ventilatory and acid-base variables were studi ed in Siberian sturgeon (Acipenser baeri) exposed to acute and severe hypoxia (Pw(O2) = 10 torr), followed by a rapid return to normoxia. Th is treatment caused a significant stress, revealed by the high levels of plasma catecholamines and cortisol. The moderate circulatory change s firstly observed would represent the effects of increased plasma cat echolamine levels together with an increased adrenergic nervous tone o n the cardiovascular system. Then, these effects were masked by a poss ible vagal reflex resulting in bradycardia. Deep hypoxia induced a ven tilatory alkalosis combined with a moderate metabolic acidosis. The la tter amplified concomitantly with a massive flush of lactate into the blood stream. The initial hyperventilation was followed by a deep vent ilatory depression. During return to normoxia, hyperventilation resume d consistent with the repayment of an oxygen debt. Thus, the sturgeon, although considered as an archaic fish, developped the same adaptativ e responses as teleosts submitted to comparable hypoxic conditions.