| Summary: | National audience Changes in respiratory, acid-base and some circulatory variables were studied in Siberian sturgeon Acipenser baeri, during progressive or acute hypoxia, followed by recovery under normoxic conditions. Submitted to progressive hypoxia, this fish is able, by increasing ventilatory activity, to maintain oxygen uptake down to a critical level of ambient oxygen partial pressure contained between 20 and 40 mmHg. During the posthypoxic period, an O2 debt is repaid, indicating that a shift to anaerobic metabolism has occured during exposure to hypoxia. Progressive hypoxia induces combination of respiratory alkalosis and metabolic acidosis. An acute hypoxia causes a significant stress revealed by high levels of plasma catecholamines. The initial hyperventilation is followed by a deep ventilatory depression. The hypertension firstly observed, although moderate, represents the effect of increased plasma catecholamines. Then, this effect is progressively masked by a possible vagal relex resulting in a bradycardia concomitant to the hypoventilation. The acid-base response are comparable to those of a progressive hypoxia, although more pronounced. However, in spite of the massive flush of lactate into the blood stream during normoxic recovery, plasma acidification remains relatively moderate due to a simultaneous increase in plasma sodium concentration. Thus, the sturgeon, although considered as an archaic fish, has developed the same adaptative responses as teleosts submitted to comparable hypoxic conditions. Les adaptations respiratoires, acido-basiques et quelques effets circulatoires ont été étudiés chez l'esturgeon sibérien Acipenser baeri lors d'une hypoxie progressive ou d'un choc hypoxique, et du retour en normoxie. Au cours d'une hypoxie progressive, ce poisson est capable, en hyperventilant, de maintenir constante sa consommation d'oxygène jusqu'à une valeur critique de pression partielle d'oxygène dans l'eau située entre 20 et 40 mmHg. Le retour en normoxie est caractérisé par le paiement ...
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