Loach Minnow

scientific name common name

Bison code 010290 ______

Official status ______Federal (USDI): threatened Endemism State AZ: threatened State NM: threatened Gila River Basin, Ariz./NM ______

Status/Threats

The loach minnow has been eliminated from about 80% of its historic range. Although common in Aravaipa Creek and portions of the Blue River Arizona, it appears to have declined in the Gila River headwaters of New Mexico over the past decade. Samples in the upper Gila in 1999 by the Rocky Mountain Research Station, Flagstaff, Arizona at over 20 sites suggested indicated loach minnow occurring from the Gila Cliff Dwellings on the West Fork of the Gila River to the Arizona-New Mexico border. Excessive substrate fines, irrigation diversions resulting in reduced streamflow, and introduced, nonnative fish appear to be threats to the species. Ictalurid catfishes which feed in riffles has the greatest potential to consume this diminutive, riffle-dwelling species.

Distribution

Formerly widely distributed in streams throughout the Gila River System, Arizona and New Mexico Presently restricted to the headwaters of the Gila, San Francisco, Blue, North and East Forks of the White and Black rivers and Eagle and Aravaipa Creek. It has been extirpated from the San Pedro River mainstream. The species may be vary widely in numbers in time and space.

Habitat

The loach minnow is a cryptic species that almost exclusively inhabits high gradient riffles (> 1%), 10-25 cm in depth with gravel/cobble substrates. Here the species breeds and feeds and lives. Habitat use appears to vary seasonally and among different stream and river drainages.

Life history and ecology

The species spends all of its life in the interstices of high gradient riffles. Here it breeds and feeds on aquatic insects, principally fly and mayfly larvae and nymphs, however stone, caddis and blackfly larvae are also part of loach minnow diet. Adult loach minnow normally attain a maximum length of 60 mm. The species moves in bursts of swimming from one substrate material to another much as darters of the eastern United States. The species is most closely associated with other native riffle dwelling species. It co-inhabits similar aquatic space with desert suckers and speckled dace. However, the species with its large pectoral fins, reduced air bladder and small scales is more favorably adapted to swift waters than its congener, speckled dace.

Breeding

Loach minnow spawn in the spring, mostly in a 4 to 6-week period in water temperatures of 16-20 C. Spring runoff duration and intensity, summer, convectional storms, and flooding all a influential factors in specific time of spawning. Adhesive eggs are deposited on the underside of flattened rocks slightly elevated off the stream bottom. Eggs are deposited in clutches of 40-100, and fecundity of females has been estimated to be up to 300 eggs for 2 year old adults. Current and lack of fine sediment are critical to spawning success. Sexual dimorphism is strong, with males becoming brilliant red on the ventral surface and especially at the fin bases. The females lack this coloration become deeply pigmented during reproductive season.

Key habitat components: current (60 cm/sec or greater), cobble-pebble substrates

Breeding season: April-May (peak), late summer to autumn following spates

Grazing effects

No data on the effects of livestock grazing on loach minnow are available. Excessive fines in substrates have been suggested as an indirect effect on reproduction and food supply. However, no data on either the amount of fines that is excessive or its link to grazing or other land uses on the watershed and in riparian-stream areas is available. The high gradient riffles inhabited by the species has a probability of cleaning substrates and moving sediment through these habitats to slower, lower gradient run and pool habitats.

Selected references

Minckley, W. L. 1973. Fishes of Arizona. Arizona Game and Fish Department. Phoenix, Arizona. 293 pp.

Propst, D. L. 1999. Threatened and endangered fishes of New Mexico. New Mexico Game and Fish Technical Report 1. Santa Fe, New Mexico. 84 pp.

Propst, D. L., K. R. Bestgen, and C. W. Painter. 1988 Distribution, status, biology and conservation of loach minnow (Tiaroga cobitis) in New Mexico. New Mexico Endangered Species Report 17: 1- 75. U. S. Fish and Wildlife Service, Albuquerque, New Mexico.

Propst, D. L. and K. R. Bestgen. 1991. Habitat and biology of the loach minnow, Tiaroga cobitis, in New Mexico. Copeia 1991: 29-39.

Rinne, J. N. 1989. Physical habitat use by loach minnow, Tiaroga cobitis, (Pisces: Cyprinidae), in southwestern desert streams. Southwest. Nat. 34(1):109-117.

Rinne, J. N. 1992. Physical habitat utilization of fish in a Sonoran Desert stream, Arizona, southwestern United States. Ecol. Freshwater Fishes 1: 1-8.

Rinne, J. N. , P. Boucher, D. Miller, A. Telles, J. Montzingo, R. Pope, B. Deason, C. Gatton, and B. Merhage. 1999. Comparative fish community structure in two southwestern desert rivers. In, S. Leon, P. Stine, and C. Springer (eds) Restoring native fish to the lower Colorado River: Interactions of native and non-native fishes: A symposium and Workshop.