No abstract

The Devils Hole pupfish, Cyprinodon diabolis, exists in an isolated cavern administered by Death Valley National Park. Only 65 adults were counted in a recent census, down from over 500 fish in 1996. Limiting factors for population recovery are high temperatures that average 33°‐34° C in the main pool and low levels of dissolved oxygen during much of the year. A refuge population of C. diabolis propagates well in our laboratory at 28° C but less so at 33° C. The critical PO2 of 33° C acclimated fish (8.39 ± 0.16 kPa) is significantly higher than that of the 28° C acclimated fish (6.49 ± 0.14 kPa). Further, the 33° C acclimated fish produce 7.3x more ethanol suggesting a large anaerobic component of total metabolic rate. We further investigated the effect of limiting oxygen levels on developing eggs. Oxygen consumption (VO2) in air saturated water prior to hatching increased as the heartbeat appeared but remained stable thereafter, even when the larva was obviously active in the egg capsule. VO2 increased markedly when the larva emerged suggesting the egg capsule is a barrier for oxygen diffusion. Surprisingly, critical PO2 of eggs was even higher than that of adults indicating an even greater reliance on anaerobic metabolism. We suggest that the reliance on anaerobic metabolism in the presence of available oxygen is a larval adaptation that persists in the adults as paradoxical anaerobism.