Cooperative Fish and Wildlife Research Units Program: Arizona
Education, Research and Technical Assistance for Managing Our Natural Resources

The Devils Hole pupfish Cyprinidon diabolis is a relic of the last ice age; stranded as receding glacial lakes moved across a drying and warming landscape. Found in a single limestone fissure in Death Valley National Park, the Devils Hole Pupfish has survived in its current location—perhaps the smallest vertebrate distribution in the world—for the last 25,000 years. The Devils Hole pupfish itself is an iridescent blue, 2.5mm-long fish that lacks pelvic fins. The spring-fed Devils Hole remains a constant 33C, and contains approximately 2 ppm dissolved oxygen. Recent, dramatic declines in the Devils Hole pupfish population have raised concerns over the future of the species. As there are no remaining refugia for pure-strain pupfish outside of Devils Hole, the possibility of extinction has become quite real. Previous lack of success for rearing fish in laboratory settings coupled with low egg viability further complicate recovery efforts. Census divers and scientists associated with the Devils Hole program have reported sighting larval pupfish on the stone shelf, as well as adult fish throughout the upper reaches of the water column. However, there are few reports of middle-age class fish, and with numbers of adults that are significantly lower than previous years, it seems that many larval fish are simply not surviving to the adult age class. Surveys have suggested that food available to larval pupfish has shifted from the 1970’s to current times. To identify if food bottlenecks to larval growth and survival are currently occurring in Devils Hole, we evaluated dietary adequacy of the most important constituents of the algal and invertebrate assemblages from the 1970’s and from 2001, as well as a flake food that is currently being used in supplemental feeding of the pupfish. To do this, we examined growth and survival of larval hybrid Devils Hole pupfish, Cyprinidon diabolis x Cyprinidon nevadensis mionectes, fed Rio Grande Silvery Minnow flake food; and monospecific cultures and combinations of cyanobacteria Cyanophyta, green algae Spirogyra spp., ostracods Ostracoda, amphipods Hyallela azteca, diatoms Bacillariophyta, and copepods Cyclopoida. We quantified survival, growth, and lifespan of larval hybrids among 14 food treatments. Larvae fed flake food had significantly higher survival and lifespan than those fed natural food types. Of the natural food types, larvae fed algae or cyanobacteria in monospecific cultures or in combination with invertebrates had the highest survival and lifespan. Pure invertebrate treatments yielded the lowest survival and lifespan. No significant difference in total length at 14 days was found among treatments. These results were presented in a thesis and are now being prepared for publication.