Desert Dace

Eremichthys acros

Description

The desert dace, Eremichthys acros, the only member of the genus Eremichthys, is about 2.5 in (7 cm) long. Under optimal conditions, individuals may occasionally reach a length of 10 in (25 cm). The desert dace is olive-green above and silvery below with dull yellow reflections along the sides. Some individuals, especially the young, have a pronounced dark streak along the middle of each side. The side scales reflect bluish and greenish iridescent in sunlight. An unusual aspect of this fish's anatomy is the presence of prominent horny sheaths on the jaws, which probably allow the fish to scrape algae from rocks. No other cyprinid possesses such a feeding adaptation.

Behavior

The desert dace feeds on algae, diatoms, and sometimes snails and insects. The horny sheaths on the jaws are probably used for grazing.

It is notable for its tolerance for high temperatures, often surviving in waters as hot as 100°F (38°C).

The desert dace probably breeds year-round and has been observed to spawn in November, March, and May. Some mature eggs are carried throughout the year but reach the highest fecundity in March and April. Captive-bred dace began producing young at an age of 13 months.

Habitat

The desert dace inhabits thermal springs and their outflows, including small irrigation ditches, where waters are warmer than 67°F (19°C). Water temperature appears to be a major factor controlling the distribution of desert dace within a spring system. In very hot springs, the dace finds its temperature range in the cooler outflow streams. Its preferred water temperature is 73.4-84.2°F (23-29°C), but it has been observed in water as hot as 105°F (40.5°C), the highest temperature ever recorded for a minnow habitat in North America.

Outflows from the numerous small springs terminate either in marshy areas or coalesce into Mud Meadow Wash. Pools that the desert dace occupy include spring pools up to 8 ft (2.4 m) in depth with little or no current and peripheral vegetation, and in small, flowing, natural channels and irrigation ditches with dense vegetation, including pond-weed, saltgrass, spikerushes, and bulrush.

Distribution

The desert dace is endemic to a group of thermal springs in the Soldier Meadows area of Humboldt County, Nevada where it survives in eight of 20 or more springs.

Threats

Most of the desert dace's habitat is privately owned. At many of the Soldier Meadows springs, water has been diverted from natural channels into concrete-lined ditches, primarily to water livestock. Channelization changes the temperature gradient of the outflows and interferes with the dace's need to locate optimal water temperatures. Additionally, artificial channels do not readily support the abundance of tiny life forms, which supply the bulk of the desert dace's diet. Two reservoirs, located 3 mi (5 km) from the habitat springs, contain many non-native fishes, such as channel catfish and small-mouth bass. There is danger that these fishes will escape into the springs and prey upon the dace.

Because Soldier Meadows is recognized for having significant geothermal resources, there is some threat of regional exploration and development of this alternative energy source. Such activities would severely disturb the thermal aquifer that feeds the local springs. Tentative geothermal wells were drilled several years ago but were eventually abandoned.

Conservation and Recovery

Critical Habitat has been designated for the desert dace to include all thermal springs and out-flows within Soldier Meadows, an area of about 8 sq mi (21 sq km). Current ongoing activities consist of a joint effort between Bureau of Land Management (BLM) and the Nevada Department of Wildlife to transplant desert dace into two springs on BLM-administered land. BLM maintains a water temperature and flow recorder on the two springs. More research needs to be conducted to determine habitat requirements of juveniles, foods and feeding habits, population dynamics, current distribution and abundance, and interaction with native and introduced species. Once these data are collected, they can be applied to the life history and ecological requirements of the species.

Contact

Regional Office of Endangered Species
U.S. Fish and Wildlife Service
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232
http://pacific.fws.gov/

References

Hubbs, C. L. and R. R. Miller. 1948. "Two New, Relict Genera of Cyprinid Fishes from Nevada." Occasional Papers of the Museum of Zoology, University of Michigan, Vol. 507.

Ono, R. D., J. D. Williams, and A. Wagner. 1983.Vanishing Fishes of North America. Stonewall Press, Washington, D.C.

U.S. Fish and Wildlife Services. 1985. "Determination of Threatened Status and Designation of Critical Habitat for the Desert Dace." Federal Register 50:50304-50309.