Common name: Gila Trout
Synonyms and Other Names: Behnke (1992) treated the Gila Trout as a subspecies (Oncorhynchus gilae gilae)
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Identification: Gila Trout have a short, stocky body that is moderately compressed and a yellowish golden body coloration (Behnke 2002, Minckley and Marsh 2009). The yellow coloration is distinctive and is deeper in color below the lateral line and more silver yellow with a golden sheen above, and the origin of the dorsal fin is nearer the caudal base than the tip of the snout (Behnke 2002, Minckley and Marsh 2009). The adipose fin is longer than other western trouts. Large spots are found on the adipose fin, fine spots above the lateral line, and no spots on the dorsal, pelvic, or anal fins (Behnke 2002).
Gila trout and Apache trout are similar in coloration however the Gila Trout have smaller, more profuse spots compared to the Apache Trout (Oncorhynchus apache). Parr marks along the sides can be present but fade in large Gila trout adults while parr marks are absent or very rare in Apache trout (Behnke 2002). Mature Gila Trout have a faint rose or pink coloration along the lateral line, which is missing from all life stages of Apache Trout (Behnke 2002, Minckley and Marsh 2009). In comparison to other western trouts, the Gila trout has a longer adipose fin.
Size: length range of 13-23 cm and weight of 28-170 g (Behnke 2002)
Native Range: Gila River system, New Mexico and Arizona, including the San Francisco drainage in Arizona and New Mexico, and the Verde and Agua Fria drainages in Arizona (Page and Burr 1991; U.S. Fish and Wildlife Service 1993).
Gila Trout have been reported in the Lower Colorado, Upper Gila-San Carlos Reservoir, Willcox Playa, Middle Little Colorado, Lower Colorado-Marble Canyon, Tonto, Lower San Pedro, Little Colorado, and Upper Little Colorado drainages in Arizona (U.S. Fish and Wildlife Service 1993).
The Gila Trout was introduced into McKnight Creek, New Mexico, a tributary of the Mimbres River in the Guzman basin (Behnke 1992; U.S. Fish and Wildlife Service 1993).
Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Oncorhynchus gilae are found here.
Table last updated 9/30/2019
† Populations may not be currently present.
Ecology: The native habitat of Gila Trout is small, cool water (< 25º C) perennial montane streams ranging from 1,660 m to over 2,800 m in elevation. These creeks usually occur in mixed conifer, montane coniferous, and sub-alpine coniferous forests (Arizona Game and Fish Department 2003). Pool habitat is critical for refuge during low flow conditions and periods of thermal extremes (Arizona Game and Fish Department 2003). Their diet consists of aquatic and terrestrial invertebrates (Behnke 2002). Adult Gila trout are typically smaller because of their diet and habitat limitations.
Gila Trout typically live four years, but the maximum known is six years (Behnke 2002). Males are sexually mature at age 1 or 2, and females mature around 172 mm total length at age 3 (Minckley and Marsh 2009). Spawning occurs in the spring or early summer (April -June). Females lay between 143-686 eggs based on body size (Nankervis 1988) and require clean coarse gravel substrates and continuous stream flow for redds (i.e., nests) (Arizona Game and Fish Department 2009).
Stocking and naturalization of non-native trout (Rainbow Trout, Oncorhynchus mykiss and Brown Trout, Salmo trutta) species in the native range of Gila Trout have impacted the species through predation and competition (Arizona Game and Fish Department 2003). Gila trout readily hybridize with rainbow trout (O. mykiss) and therefore have lost some of its genetic integrity at some populations (U.S. Fish and Wildlife Service 1993).
Means of Introduction: This endangered species was intentionally stocked to increase its distribution. McKnight Creek was stocked in November 1970 with 307 fish from Main Diamond Creek. The creek was restocked in April 1972 with 110 fish from Main Diamond Creek to supplement the population stocked in 1970 after a severe drought in 1971 that reduced its numbers to less than 20. Flooding in 1988 resulted in a loss of greater than 90 percent of the population. The creek was restocked in October 1989 with 200 trout from Main Diamond Creek (U.S. Fish and Wildlife Service 1993).
Status: Established in McNight Creek, New Mexico (U.S. Fish and Wildlife Service 1993).
The only remaining pure population of Gila trout is believed to be found in Spruce Creek, a creek in the San Francisco drainage of the Gila River system (Propst et al. 1992; Behnke 2002). Barrier falls separate the population from non-native trout in the system.
Impact of Introduction: The impacts of this species are currently unknown, as no studies have been done to determine how it has affected ecosystems in the invaded range. The absence of data does not equate to lack of effects. It does, however, mean that research is required to evaluate effects before conclusions can be made.
References: (click for full references)
Arizona Game and Fish Department, New Mexico Department of Game and Fish, U.S. Fish and Wildlife Service, U.S. Forest Service. 2003. Gila Recovery Plan. Western Native Trout Status Report.
Behnke, R.J. 1992. Native trout of western North America. American Fisheries Society Monograph 6. American Fisheries Society, Bethesda, MD.
Behnke, R.J. 2002. Trout and Salmon of North America. The Free Press, NY.
Minckley, W.L., and P.C. Marsh. 2009. Inland fishes of the greater Southwest: chronicle of a vanishing biota. University of Arizona Press, Tucson, AZ.
Page, L.M., and B.M. Burr. 1991. A field guide to freshwater fishes of North America north of Mexico. Volume 42. Houghton Mifflin Company, Boston, MA.
Propst, D. L., J. A. Stefferud, and P. R. Turner. 1992. Conservation and status of the Gila Trout, Oncorhynchus gilae. The Southwestern Naturalist 37:117-125.
U.S. Fish and Wildlife Service. 1993. Gila Trout Recovery Plan (second revision). Albuquerque, New Mexico.
U.S. Fish and Wildlife Service. 2003. Gila Trout Recovery Plan (third revision). Albuquerque, New Mexico.
U.S. Fish and Wildlife Service. 2006. Federal Register, Endangered and Threatened Wildlife and Plants; Reclassification of the Gila Trout (Oncorhynchus gilae) From Endangered to Threatened; special Rule for Gila Trout in New Mexico and Arizona. 71 (137): 40657-40674.
Fuller, P. and Daniel, W.M.
Revision Date: 9/4/2019
Peer Review Date: 9/4/2019
Fuller, P. and Daniel, W.M., 2020, Oncorhynchus gilae (Miller, 1950): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=905, Revision Date: 9/4/2019, Peer Review Date: 9/4/2019, Access Date: 11/26/2020
This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.