PaO2 changes during rapid PwO2 changes in 2 teleosts with different biotopes: Salmo gairdnerii and Ictalurus melas (author's transl).

PaO2 and ventilation measurements in Salmo gairdnerii and Ictalurus melas (brown bullhead) were performed during progressive or step changes of PwO2. 10 In Salmo, out of stress conditions at 15 degrees C, the PaO2--PwO2 curve shows a plateau related to the PwO2 values above adaptation (155 torr). The PaO2 value corresponds to the O2 maximum saturation of the arterial blood. In contrast, in Salmo under stress conditions, PaO2 increases linearly with PwO2. During a hypoxic step change, PaO2 displays a biphasic modification, with a rapid decrease followed by a progressive increase up to the PwO2 value. During an hyperoxic step change, the PaO2 increase is of small amplitude. 20 When Ictalurus is under stress conditions the PaO2-PwO2 curve is almost linear. When out of stress conditions at 15 degrees C and below, the PaO2 oscillates between zero and values close to PwO2 in relation to successive periods of apnoea. During a hypoxic step change, the amplitude of the PaO2 oscillations decreases, the lower values being higher than under normoxic conditions. 30 These experiments show that PaO2 is an important parameter of ventilatory regulation in Salmo, but probably not in Ictalurus.