Paradoxical anaerobism in desert pupfish

Abstract

Pupfish in the genus Cyprinodon migrated into the Mojave Desert when the region contained a network of large lakes and interconnecting streams. Climate change over the past ten thousand years has resulted in isolated populations in remaining warm springs and pools. Devils Hole is such a pool with stable temperatures between 33 and 34° C and a small population of C. diabolis whose population fell to 38 adult fish counted in 2006. Reproduction occurs on a shallow ledge where temperatures range from 26° C in the winter to 39° C in the summer. We hypothesized that the warm temperatures of the pool were detrimental to the fish. We used a refuge population of C. diabolis to measure oxygen consumption (VO2) of fish acclimated to 28 and 33° C. The 28° C acclimated group (Control) showed a consistent pattern of VO2 over a 2–4 hour experimental period. The 33° C acclimated group showed three patterns: 1) Predictable, i.e. like the 28° C group. 2) Variable, fluctuated between depressed VO2 and values near that of the Predictable group. 3) Intermittent, characterized by periods where VO2 virtually ceased for as long as 67 minutes. Fish showing intermittent VO2 were actively ventilating. Fish acclimated to 33° C produced 7.3X more ethanol than fish acclimated to 28° C indicating use of anaerobic metabolism despite the availability of oxygen.