Physiological and Metabolic Responses of Juvenile American Paddlefish to Hypoxia and Temperature

The American paddlefish (Polyodon spathula) is a declining, primitive, migratory fish, and an important aquaculture species. Hypoxia is an increasing problem in the natural habitats that the paddlefish has historically inhabited, and is a potential problem in managed culture conditions. However, the effects of hypoxia on paddlefish are not well understood. Therefore, in order to understand the effects of hypoxia on juvenile paddlefish, acute hypoxia tolerance was measured. Further, aerobic metabolic rates and swimming capabilities were measured in an intermittent respirometer or swim flume under normoxic (PO₂ = 140-155 mm Hg) and hypoxic (PO₂ = 62-70 mm Hg) conditions at 18^oC and 26°C. The results showed that paddlefish acclimated to 18^oC and 26^oC have a critical partial pressure of oxygen of 74 mm Hg (4.70 mg/L) and 89 mm Hg (4.84 mg/L), respectively. Paddlefish had a lethal oxygen threshold of ~2 mg/L in both temperatures. Further, paddlefish exhibited a reduction in swimming capabilities (U_crit) when exposed to hypoxia with a 24% and 41% decrease in U_crit at 18^oC and 26^oC, respectively. Therefore, paddlefish are relatively sensitive to hypoxia, and at temperatures from 18-26°C require a dissolved oxygen concentration ≥ 4.7 mg/L to maintain basal aerobic metabolism and ≥ 2.0 mg/L to survive under acute hypoxia.