The effects of dissolved gases on oxygen consumption rate and ventilation frequency in white sturgeon, Acipenser transmontanus

The effects of low oxygen (hypoxia; PO2 ca. 85 mmHg) and high carbon dioxide (hypercapnia; PCO2 ca. 20 mmHg) water tensions on routine oxygen consumption rate ( MO) and ventilation frequency (Vf) were studied in the white sturgeon, Acipenser transmontanus. Control MO2 and Vf during normoxic normocapnic (NN) conditions were 36.7 +/- 0.4 mg O-2 h(-1) and 91 +/- 5.6 breaths min(-1), respectively. Hypoxic normocapnic (HN) conditions had no effect on MO2 but increased Vf significantly (120 +/- 3.6 breaths min(-1)) and with the resumption of NN, Vf dropped significantly (75 +/- 2.4 breaths min(-1)). The hypoxic hypercapnic (HH) and normoxic hypercapnic (NH) exposures produced signi cant elevations in MO2 and Vf, to 71 +/- 0.8 mg O-2 h(-1) and 139 +/- 3.0 breaths min(-1) ( HH), and 61 +/- 0.6 mg O-2 h(-1) and 124 +/- 3.3 breaths min(-1) ( NH), respectively. Following HH and NH exposures and after the return to the NN condition, MO2 was significantly higher than control MO2, and Vf was significantly less than control Vf. Despite hypoxia-induced tachypnea, hypoxia does not significantly increase MO2. However, hypercapnia, with or without hypoxia, is a stressor that significantly increases MO2 and Vf.