Oncorhynchus gilae

Geographic Range

Gila trout are found in freshwater streams of the American Southwest. They can be found in the upper Gila River watershed in New Mexico, and the Francisco River watershed in Arizona. Historically, Gila trout also inhabited the Verde and Agua Fria Rivers in Arizona, but due to competition from introduced trout, sedimentation from grazing and wildfires, and stream flow alterations, Gila trout became extirpated from these rivers. Efforts to restore viable populations were unsuccessful and few, if any, Gila trout survived. The majority of extant Gila trout populations occur within federally managed lands and designated wilderness areas.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Gila trout live in freshwater rivers and perennial streams at elevations from 1,650 m to 2,800 m. The majority of their habitat consists of cold headwater and moderate valley streams that rarely exceed 21°C. The headwater streams are steep, with rocky cascades and pools, and gradients of up to 12%. The valley streams are typically meandering, with cobble riffles and pools around large woody debris and rocks, and gradients of around 3%. The predominant substrate for good habitat tends to be gravel, ranging in size from 2 mm to 9 mm. The primary riparian vegetation in these habitats, from lower to higher elevations, consists of Arizona alder ( Alnus oblongifolia ), western box elder ( Acer negundo ), willow ( Salix sp.), narrowleaf cottonwood ( Populus angustifolia ), ponderosa pine ( Pinus ponderosa ), blue spruce ( Picea pungens ), white fir ( Abies concolor ), and quaking-aspen ( Populus tremuloides ).

• Habitat Regions
• temperate temperate
• freshwater freshwater

• Aquatic Biomes
• rivers and streams

Physical Description

Adult Gila trout are 13 to 23 cm in length and generally weigh from 28 to 170 g. They are a golden-yellow color, with small dark spots above the lateral line and a larger dark spot on the adipose fin. The tips of the dorsal, pelvic, and anal fins are tipped with yellow or white. Their sides often have a pinkish lateral band, which gets darker in males during the spawning season. Juvenile parr marks are often retained through adulthood and most mature specimens have a yellow cutthroat mark.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger
• sexes colored or patterned differently
• male more colorful

Development

Eggs are laid and fertilized in redds, where they incubate. After 8 to 10 weeks, fry emerge at about 15 mm to 25 mm in length. The young fish typically reach 50 mm to 100 mm by the autumn of their first year, with elevation and corresponding temperatures being the main limiting factor for growth. Little additional growth occurs over the winter. By the autumn of their second year they generally reach 150 mm to 160 mm. After the third year, growth slows down. Adults range from 150 mm to 230 mm, depending on their habitat. Sex determination has not been studied in Gila trout, but studies of other species in the genus Oncorhynchus have shown that sex determination is mainly genetic, but that temperature may also influence gonadal sex differentiation.

• Development - Life Cycle
• indeterminate growth indeterminate growth

Reproduction

Gila trout spawn in the spring when water temperatures begin to warm. Though little research has been done on the mating systems and behavior of Gila trout specifically, extensive research has been conducted on closely related species in the genus Oncorhynchus . Males increase their reproductive success quantitatively, by mating with as many females as possible, while females select the best nesting sites. Females search for nesting sites with suitable gravel, water depth, and velocity. For Gila trout, this gravel size ranges from 2-9 mm, in water depths of 6-15 cm. Once a female finds a suitable site, she will begin to build her nest. Females construct nests by turning on their side and rapidly beating their tails. They test the nest's completeness and depth with their pelvic fins. Gila trout nests, or redds, are typically 3-4 cm in depth and one-fourth the width of the stream (approximately 1 m^2). While females finish building their nests, males will begin to court. Courting behavior involves the male swimming along the female and quivering intensely, and gently nudging the female’s side with their snout. The most dominant male, based on size and aggression, is typically selected. The male and female will then occupy the area above the redd. Other less dominant males will often swim alongside the pair, waiting for a chance to spawn with the female. These males typically get chased away by the dominant male when they are too close. Just before releasing eggs, females begin to vibrate and gape, at which point the dominant male (and sometimes others) will join her in the nest. She then lays her eggs in the gravel nest and the males emit their sperm. When the female is done laying eggs, she covers them with gravel by gently digging upstream of the nest.

• Mating System
• polygynous polygynous

Gila trout spawn when water temperatures reach 8°C. This is typically from March to June, depending on elevation. Females will lay one redd, containing an average of 150 eggs per year. Fry hatch in 8 to 10 weeks. For every 100 eggs, about 50 fry hatch. Females reach sexual maturity in 2 to 4 years, and males reach sexual maturity in 2 to 3 years. Due to their relatively short lifespan, females are typically only able to spawn twice, while males will spawn 3-4 times.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • external external
• oviparous oviparous

There are no reports of parental care in this species beyond the construction of redds by females.

• Parental Investment
• no parental involvement

Lifespan/Longevity

Gila trout can live 3 to 10 years, but most live only about 4 years. The mortality rate for Gila trout is high, especially for young individuals. Of every 100 eggs hatched, about 50 will survive to the juvenile stage. Only 6 will make it to the subadult stage, and 2 will survive to the adult stage.

Behavior

Gila trout are generally sedentary, though there are reports of individuals moving over distances up to 1.5 km. Juveniles and subadults tend to stay in riffles, while adults tend to inhabit pools. Gila trout will defend their territory from others. They typically live alone but become more social during spawning season.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• motile motile
• sedentary sedentary
• solitary solitary
• territorial territorial
• dominance hierarchies dominance hierarchies

Home Range

Though it is known that Gila trout will defend a territory from conspecifics, there is no published data available regarding the size of these territories, or the home ranges inhabited by these fish.

Communication and Perception

Like other trout species, Gila trout use their eyesight for hunting, as well as their lateral line system, which is able to detect movements of prey items in the water. Intraspecific communication is mostly accomplished through body movements, such as nudging, quivering, biting, and digging. Social rank and dominance is established through aggressive movements and fighting. Social rank is primarily important during the breeding season, but is also critical during times of low water levels, when pools become crowded. During these times, dominant fish will chase others out of their territory.

• Communication Channels
• visual visual
• tactile tactile

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• vibrations vibrations
• chemical chemical

Food Habits

Gila trout are insectivores. Throughout the year, their diet is comprised of a changing assortment of macroinvertebrates. They feed primarily on dipterans , trichopterans , ephemeropterans , and coleopterans . They have also been known to eat other fish when invertebrate food resources are low. They generally feed in the morning and early afternoon. Once an individual establishes a feeding area, it will become very protective of it and chase other fish away. Due to the nature of the habitat that Gila trout live in, many fish can be crowded into a small pool at times of low water flow, causing food shortages that can lead to many fish starving to death.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore

• Animal Foods
• fish
• insects

Predation

Predators for Gila trout include birds, bears, and other fishes. Young Gila trout will sometimes be preyed upon by adult conspecifics.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Gila trout are active predators, eating other small fish and insects. Gila trout fry are prey for birds and larger fishes.

Economic Importance for Humans: Positive

Gila trout have no economic importance for humans.

Economic Importance for Humans: Negative

Gila trout have no major negative economic importance for humans. There are fishing restrictions in Gila trout habitat, but due to the small size and remote locations of these streams, the economic impacts are small.

Conservation Status

Gila trout were first recognized as endangered under the Federal Endangered Species Preservation Act of 1966 and later listed as threatened under the Endangered Species Act of 1973. They are listed as a threatened species by the New Mexico Department of Game and Fish and a Species of Concern by the Arizona Game and Fish Department.

Drought, sedimentation from logging, run off, grazing, and forest fires all pose serious threats to Gila trout populations. Habitat invasion by exotic trout has also had a negative impact. To help the maintain this species, pure genetic strains are being raised in hatcheries and stocked into historic Gila trout ranges. Also, exotic trout are being actively removed and fish barriers built to prevent new invasions.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Austen Lorenz (author), Sierra College, Jennifer Skillen (editor), Sierra College, Jeremy Wright (editor), University of Michigan-Ann Arbor.

References

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Behnke, R. 2002. Trout and Salmon of North America . New York: The Free Press.

Brown, D., A. Echelle, D. Propst, J. Brooks, W. Fisher. 2001. Catastrophic Wildfire and Number of Populations as Factors Influencing Risk of Extinction for Gila Trout ( Oncorhynchus gilae ). Western North American Naturalist , 61/2: 139-148. Accessed April 28, 2013 at https://ojs.lib.byu.edu/ojs/index.php/wnan/article/viewFile/987/848 .

Dowling, T., M. Childs. 1992. Impact of Hybridization on a Threatened Trout of the Southwestern United States. Conservation Biology , 6/3: 355-364. Accessed April 28, 2013 at http://www.jstor.org/discover/10.2307/2386036?uid=3739256&uid=2129&uid=2&uid=70&uid=4&sid=21102398187277 .

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Propst, D., J. Stefferud. 1997. Population Dynamics of Gila Trout in the Gila River Drainage of the South-western United States. Journal of Fish Biology , 51/6: 1137-154. Accessed April 28, 2013 at http://onlinelibrary.wiley.com/doi/10.1111/j.1095-8649.1997.tb01132.x/abstract .

Rinne, J. 1980. Spawning Habitat and Behavior of Gila Trout, a Rare Salmonid of the Southwestern United States. Transactions of the American Fisheries Society , 109/1: 83-91. Accessed April 28, 2013 at http://www.tandfonline.com/doi/abs/10.1577/1548-8659%281980%29109%3C83%3ASHABOG%3E2.0.CO%3B2#preview .

Yano, A., B. Nicol, K. Valdivia. 2011. Sex in Salmonids: From Gonadal Differentiation to Genetic Sex Determination. Indian Journal of Science and Technology , 4/8: 60-61. Accessed April 28, 2013 at http://www.indjst.org/index.php/indjst/article/view/30789 .

NatureServe. 2012. " Oncorhynchus gilae " (On-line). NatureServe Explorer. Accessed April 03, 2013 at http://www.natureserve.org/explorer/servlet/NatureServe?searchName=Oncorhynchus+gilae .

U.S. Forest Service. Oncorhynchus gilae . 2009. Phoenix, AZ: U.S. Forest Service. 2009. Accessed May 05, 2013 at http://www.fs.fed.us/outernet/r3/tonto/naturalResources/wildlife/speciesNativ/GILTROUT.ANM.pdf .

Arizona Game and Fish Department. Animal Abstract Oncorhynchus gilae . 2002. Phoenix, AZ: Arizona Game and Fish Department. 2002.

U.S. Fish and Wildlife Service. Gila trout ( Oncorhynchus gilae ) Recovery Plan (Third Revision). Technical Review Draft April 2002. Albuquerque, New Mexico: U.S. Fish and Wildlife Service. 2002. Accessed April 04, 2013 at http://www.fws.gov/southwest/es/arizona/Documents/RecoveryPlans/Gila_Trout_Recovery_Plan_(Draft_3rd_revised).pdf .

Wildscreen. 2010. "Gila trout ( Oncorhynchus gilae )" (On-line). Arkive. Accessed April 03, 2013 at http://www.arkive.org/gila-trout/oncorhynchus-gilae/image-G88214.html .

2013. "Gila trout ( Oncorhynchus gilae )" (On-line). U.S. Fish and Wildlife Service Species Profile. Accessed April 28, 2013 at http://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=E00E .

U.S. Fish and Wildlife Service. Spotlight Species Action Plan. 2009. Lead Field Office: New Mexico Ecological Services: U.S. Fish and Wildlife Service. 2009. Accessed April 07, 2013 at http://www.fws.gov/ecos/ajax/docs/action_plans/doc3047.pdf .