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Oncorhynchus gilaeGila trout(Also: Salmon)

By Austen Lorenz

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. ("Animal Abstract Oncorhynchus gilae", 2002; "Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; Behnke, 2002; Brown, et al., 2001)

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). ("Animal Abstract Oncorhynchus gilae", 2002; "Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; Behnke, 2002; Brown, et al., 2001; Propst and Stefferud, 1997)

  • Aquatic Biomes
  • rivers and streams
  • Range elevation
    1,650 to 2,800 m
    to ft

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. ("Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; Behnke, 2002; "Animal Abstract Oncorhynchus gilae", 2002; "Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; "Gila trout (Oncorhynchus gilae)", 2013; "Spotlight Species Action Plan", 2009; Behnke, 2002; "Oncorhynchus gilae", 2012; "Gila trout (Oncorhynchus gilae)", 2010)

  • Sexual Dimorphism
  • male larger
  • sexes colored or patterned differently
  • male more colorful
  • Range mass
    28 to 170 g
    0.99 to 5.99 oz
  • Range length
    13 to 23 cm
    5.12 to 9.06 in

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. ("Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; "Animal Abstract Oncorhynchus gilae", 2002; "Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; Baroiller and D'Cotta, 2001; Behnke, 2002; Propst and Stefferud, 1997; Rinne, 1980; Yano, et al., 2011)

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. ("Animal Abstract Oncorhynchus gilae", 2002; "Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; Behnke, 2002; Esteve, 2005; Propst and Stefferud, 1997; Rinne, 1980)

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. ("Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; "Spotlight Species Action Plan", 2009; Behnke, 2002; Rinne, 1980)

  • Breeding interval
    Gila trout breed once yearly.
  • Breeding season
    Spawning occurs anywhere from March to June, depending on water temperature.
  • Range number of offspring
    90 to 200
  • Average number of offspring
    150
  • Range time to hatching
    8 to 10 weeks
  • Range age at sexual or reproductive maturity (female)
    2 to 4 years
  • Average age at sexual or reproductive maturity (female)
    2 years
  • Range age at sexual or reproductive maturity (male)
    2 to 3 years
  • Average age at sexual or reproductive maturity (male)
    2 years

There are no reports of parental care in this species beyond the construction of redds by females. (Rinne, 1980)

  • 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. ("Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; Behnke, 2002; Rinne, 1980)

  • Range lifespan
    Status: wild
    9 (high) years
  • Typical lifespan
    Status: wild
    3 to 10 years
  • Average lifespan
    Status: wild
    4 years

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. ("Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; Behnke, 2002; Propst and Stefferud, 1997; Rinne, 1980)

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. (Behnke, 2002; Rinne, 1980)

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. ("Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; Esteve, 2005; Rinne, 1980)

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. ("Animal Abstract Oncorhynchus gilae", 2002; "Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; Behnke, 2002; Propst and Stefferud, 1997)

  • 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. ("Animal Abstract Oncorhynchus gilae", 2002; "Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; "Gila trout (Oncorhynchus gilae)", 2013; Behnke, 2002; "Oncorhynchus gilae", 2012; "Gila trout (Oncorhynchus gilae)", 2010)

  • Anti-predator Adaptations
  • cryptic
  • Known Predators
    • Birds
    • Bears
    • Gila trout (Oncorhynchus gilae)

Ecosystem Roles

Gila trout are active predators, eating other small fish and insects. Gila trout fry are prey for birds and larger fishes. ("Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; Behnke, 2002; Propst and Stefferud, 1997)

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. ("Animal Abstract Oncorhynchus gilae", 2002; "Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; "Gila trout (Oncorhynchus gilae)", 2013; "Spotlight Species Action Plan", 2009; "Gila trout (Oncorhynchus gilae)", 2010)

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. ("Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; "Gila trout (Oncorhynchus gilae)", 2013; "Spotlight Species Action Plan", 2009; Behnke, 2002)

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. ("Gila trout (Oncorhynchus gilae) Recovery Plan (Third Revision)", 2002; "Gila trout (Oncorhynchus gilae)", 2013; "Spotlight Species Action Plan", 2009; Behnke, 2002)

Contributors

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

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

threatened

The term is used in the 1994 IUCN Red List of Threatened Animals to refer collectively to species categorized as Endangered (E), Vulnerable (V), Rare (R), Indeterminate (I), or Insufficiently Known (K) and in the 1996 IUCN Red List of Threatened Animals to refer collectively to species categorized as Critically Endangered (CR), Endangered (EN), or Vulnerable (VU).

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

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.

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.

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.

Baroiller, J., H. D'Cotta. 2001. Environment and Sex Determination in Farmed Fish. Comparative Biochemistry and Physiology, 130/4: 399-409. Accessed April 28, 2013 at http://www.sciencedirect.com/science/article/pii/S1532045601002678.

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.

Esteve, M. 2005. Observations of Spawning Behaviour in Salmoninae: Salmo, Oncorhynchus and Salvelinus. Reviews in Fish Biology and Fisheries, 15/1: 1-21. Accessed April 28, 2013 at http://link.springer.com/article/10.1007%2Fs11160-005-7434-7.

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.

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