The mechanisms of adaptation that allow the teleost Silurus glanis to maintain its resting oxygen consumption constant when the O2 partial pressure (PO2) m the inspired water (PIO2) varied between 40 and 3kPa were studied at 13 °C. Steadystate values of oxygen consumption, ventilatory and circulatory flow rates, PO2 in the inspired and expired water, PO2 and O2 concentration in the arterial and venous blood, haematocrit and acid--base status in the arterial blood were determined after 1-day exposures at selected PIO2 values. Whole-blood O2-binding characteristics were also determined.

The key adaptation after 1 day of acclimation was maintenance of oxygen consumption by ventilatory adjustment with no change in blood flow rate or pH (no Bohr effect). At each PIO2 value (i) the ventilatory adjustment was minimal as the O2 extraction coefficient from water always remained around 80–90 % and (ii) PaO2 stayed constant at about 2kPa. Data are compared with previous results in crayfish and other teleosts. It is concluded that the principle of a constant O2 status in themilieu intérieur -- independent of large changes in PIO2 for a given state of activity -- should be valid in many crustaceans and teleosts.

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