Implications of chronic hypoxia during development in red drum.

Respiratory plasticity is a beneficial response to chronic hypoxia in fish. Red drum, a teleost that commonly experiences hypoxia in the Gulf of Mexico, have shown respiratory plasticity following sublethal hypoxia exposure as juveniles, but implications of hypoxic exposure during development are unknown. We exposed red drum embryos to hypoxia (40% air saturation) or normoxia (100% air saturation) for 3 days post fertilization (dpf). This time frame encompasses hatch and exogenous feeding. At 3 dpf, there was no difference in survival and no change in size. After the 3-day hypoxia exposure, all larvae were moved and reared in common normoxic conditions. Fish were reared for ∼3 months and measured for implications of the developmental hypoxia exposure on swim performance and whole-animal aerobic metabolism. We used a cross design wherein fish from normoxia (N=24) were swam in Blazka swim tunnels in both hypoxia (40%, n=12) and normoxia (100%, n=12), and likewise for hypoxia-exposed fish (N=20, n=10 each group). Oxygen consumption, critical swim speed (Ucrit), critical oxygen threshold (Pcrit), and mitochondrial respiration were measured. Hypoxia-exposed fish had higher aerobic scope, maximum metabolic rate, and higher liver mitochondrial efficiency relative to control fish in normoxia. Interestingly, hypoxia-exposed fish showed increased hypoxia sensitivity (higher Pcrit), and recruit burst swimming at lower swim speeds relative to control fish. These data provide evidence that hypoxia exposure leads to a complex response in later life.