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Oncorhynchus aguabonitaGolden trout

By Steve Gallas

Geographic Range

California golden trout (Oncorhynchus aguabonita) is native to the southwestern United States, specifically the Sierra Nevada region and the Golden Trout Wilderness in California. They are also found in streams in the Inyo National Forest. Within these regions, California golden trout populate streams in the Kern Plateau, located within the southern Sierra Nevada. (Knapp and Dudley, 1990; Knapp and Matthews, 1996; Matthews, 1996a; Matthews, 1996b; Stefferud, 1993)

Habitat

California golden trout are found in streams and lakes at elevations between 795 and 3,657 m. They mostly use slow-moving, meandering streams that are wide and shallow with sand or gravel bottoms. (Heckman, 1974; Knapp and Dudley, 1990; Knapp and Matthews, 1996; Stefferud, 1993)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • Range elevation
    795 to 3657 m
    2608.27 to 11998.03 ft

Physical Description

California golden trout are brightly colored, with gold or yellow ventral sides and olive green dorsal sides. They have about 10 ventral spots, arranged randomly, and a single horizontal orange stripe along both sides. There is no difference between males and females in appearance or size.

In their first year after hatching, California golden trout reach about 4.5 cm in total length, and can reach up to 12 cm in their second year. California golden trout reach maturity around 3 years old, at which point they measure about 19 cm long. ("Conservation assessment and strategy for the California golden trout (Oncorhynchus mykiss aguabonita), Tulare County, California", 2004; Knapp and Dudley, 1990)

  • Sexual Dimorphism
  • sexes alike
  • Average length
    19 cm
    7.48 in

Development

California golden trout are approximately 25 mm long when they hatch. They are independent upon birth and begin feeding almost immediately after hatching. California golden trout exhibit rapid growth within their first year, doubling in size and weight within 2 weeks of hatching.

By the time they are 1 year old, California golden trout are 4.5 cm long on average (range: 2 to 6 cm). They grow to an average of 12 cm at 2 years old and 19 cm at 3 years old. Exact growth rates depend on habitat; California golden trout living in lakes grow faster than those living in streams. In either case, California golden trout can reach lengths up to 29.3 cm. By 3 or 4 years of age, California golden trout reach sexual maturity. ("Conservation assessment and strategy for the California golden trout (Oncorhynchus mykiss aguabonita), Tulare County, California", 2004; Knapp and Dudley, 1990)

Reproduction

California golden trout are polygynandrous, meaning both males and females mate with multiple individuals. They exhibit external fertilization of eggs. Female California golden trout construct depressions known as a "redds" in which they lay unfertilized eggs. Male California golden trout then swim over the eggs and release sperm. Their movement over the eggs also causes sediment to cover the redds, which helps protect and incubate developing eggs. ("Conservation assessment and strategy for the California golden trout (Oncorhynchus mykiss aguabonita), Tulare County, California", 2004; Knapp and Preisler, 1999; Knapp and Vredenburg, 1996)

California golden trout reach sexual maturity at either 3 or 4 years of age. Spawning occurs during late May and extends through June, but the primary determinant of spawning events is water temperature. The ideal temperature for spawning is 7 to 10 °C, and changes in the temperature can delay reproduction.

Once California golden trout reach sexual maturity, females construct depressions, or "redds", in stream beds and lay 300 to 2,300 eggs. When males recognize these redds, they release sperm to externally fertilize the eggs and then they push sediment over the redds. It is not explicitly documented how male California golden trout are attracted to eggs. However, in other trout species, some degree of chemical signaling is involved in the process.

Egg incubation time depends on water temperature, but eggs that incubate at 14 °C hatch after approximately 20 days. ("Conservation assessment and strategy for the California golden trout (Oncorhynchus mykiss aguabonita), Tulare County, California", 2004; Knapp and Matthews, 1996; Knapp and Preisler, 1999)

  • Breeding interval
    Golden trout spawn at yearly intervals
  • Breeding season
    Late May through June
  • Range number of offspring
    300 to 2300
  • Average time to hatching
    20 days
  • Range age at sexual or reproductive maturity (female)
    3 to 4 years
  • Range age at sexual or reproductive maturity (male)
    3 to 4 years

Like most species of fish, California golden trout have no attachment to their breeding partners, and neither sex puts any parental investment into their offspring beyond the act of constructing a safe depression in the stream bed, known as a "redd". Females construct redds in which they lay their eggs and males cover redds with sediment once they have fertilized the eggs within. ("Conservation assessment and strategy for the California golden trout (Oncorhynchus mykiss aguabonita), Tulare County, California", 2004; Knapp and Preisler, 1999; Knapp and Vredenburg, 1996)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning
    • protecting
      • male
      • female

Lifespan/Longevity

Typically, California golden trout live up to 9 years in their native streams. However, they can live up to 20 years in an undisturbed, low-productivity stream. Unfortunately, little information exists about the longevity of California golden trout in areas where they are non-native. ("Conservation assessment and strategy for the California golden trout (Oncorhynchus mykiss aguabonita), Tulare County, California", 2004; Knapp and Dudley, 1990)

  • Range lifespan
    Status: wild
    20 (high) years
  • Average lifespan
    Status: wild
    9 years

Behavior

California golden trout are diurnal, motile, and social.

California golden trout are closely related to rainbow trout (Oncorhynchus mykiss) and share many social behaviors with this species. Rainbow trout are territorial to a certain degree, but will travel in schools. However, California golden trout are not as aggressive as rainbow trout, and are often outcompeted or preyed upon by rainbow trout and other trout species. California golden trout are similarly outcompeted when they are introduced into streams outside of their native range. ("Conservation assessment and strategy for the California golden trout (Oncorhynchus mykiss aguabonita), Tulare County, California", 2004; Tabor, 1991)

Home Range

California golden trout have diel movements of up to 8 km upstream or downstream. They forage for food within this range. Home range sizes vary by individual or based on interactions with other species in the same area. California golden trout are not particularly aggressive and do not actively defend a territory. (Knapp and Dudley, 1990; Knapp and Vredenburg, 1996; Tabor, 1991)

Communication and Perception

California golden trout are social and use a variety of methods to perceive their environment. They rely on chemoreceptors to recognize members of the same species and detect predators. They also have a lateral line system, which allows them to detect vibrations in the water. This helps them recognize potential predators.

Other trout species can avoid predation by detecting chemical signals secreted by predators. It is possible that California golden trout are capable of detecting such chemicals.

California golden trout presumably communicate visually, recognizing conspecifics based on their distinct color patterns. ("Conservation assessment and strategy for the California golden trout (Oncorhynchus mykiss aguabonita), Tulare County, California", 2004; Grubb, 2003; Randall, 2014; Tabor, 1991)

Food Habits

Both adult and juvenile California golden trout have a diet composed almost entirely of aquatic insects. They primarily feed on insects at the surface of the water, such as dipteran midges and caddisflies. California golden trout also prey on zooplankton known as common water fleas (genus Daphnia), but this is mostly in habitats outside of their native range. California golden trout occasionally consume smaller fishes and small crustaceans. (Fisk, et al., 2007; Knapp and Dudley, 1990)

  • Animal Foods
  • fish
  • insects
  • aquatic crustaceans
  • zooplankton

Predation

California golden trout are not frequently observed as being prey items for native birds and mammals. However, they are a common prey item for invasive brown trout (Salmo trutta), which eat California golden trout of all sizes.

California golden trout have several antipredator adaptations. They rely on lateral line systems to sense waves traveling through the water as a way to locate predators. Certain species of trout also avoid predation by detecting chemical signals secreted by predators. This helps trout avoid areas with predators. ("Conservation assessment and strategy for the California golden trout (Oncorhynchus mykiss aguabonita), Tulare County, California", 2004; Randall, 2014)

Ecosystem Roles

California golden trout are hosts to a variety of parasites that inhabit their gills, such as protozoans (Costia pyriformis, Ichthyophthirius multifiliis [causes the aquarium disease, "ick"], and Gyrodactylus). They are also infected by the digenetic trematode species Crepidostomum farionis. California golden trout eat species of invertebrates and Daphnia that live in their streams. Historically, California golden trout were top predators in their native streams. However, due to the introduction of species such as rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta), California golden trout are no longer top predators and instead serve as prey items for these invasive trout species. ("Conservation assessment and strategy for the California golden trout (Oncorhynchus mykiss aguabonita), Tulare County, California", 2004; Heckman, 1974)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

California golden trout are economically important for humans. Recreational fishing of California golden trout brings in revenue for national parks and local communities surrounding Golden Trout Wilderness. It has been estimated that recreational fishing in Golden Trout Wilderness brings in $147,000 to $700,000 in revenue for surrounding communities, annually. Recreational fishing of California golden trout brings in money via fishing permits, guided fishing tours, and lodging in the surrounding areas. Their economic value as a food source is not very widely reported, but it does not bring in as much revenue as other trout species caught in recreational fishing. ("Economic value of golden trout fishing in the Golden Trout Wilderness, California", 2003)

Economic Importance for Humans: Negative

There are no known adverse economic impacts of California golden trout on humans. ("Conservation assessment and strategy for the California golden trout (Oncorhynchus mykiss aguabonita), Tulare County, California", 2004)

Conservation Status

California golden trout are not evaluated under the IUCN Red List, the CITES appendices, or the U.S. federal list. The reason for this lack of evaluation is that many consider California golden trout to be a subspecies of rainbow trout (Oncorhynchus mykiss), which is not endangered.

California golden trout are limited to a small geographic range. When other species are present in the same waterways, other fish species tend to outcompete California golden trout; this is true for native and non-native populations. Brown trout (Salmo trutta) are known to prey upon California golden trout and outcompete California golden trout in their native streams.

Another threat to California golden trout populations comes from hybridization with rainbow trout. Recent studies show that introgression is happening in areas where rainbow and golden trout exist in sympatry. Furthermore, habitat degradation as the result of cattle grazing and dams made by beavers (Castor canadensis) pose threats to California golden trout populations.

The state of California has developed many possible solutions to preserve California golden trout. Ideas include setting up refuges for California golden trout where hybridization cannot occur, establishing refuges safe from predation from invasive fish species, and developing laws to prevent the continued introduction of other fish species into native habitats of California golden trout. ("Conservation assessment and strategy for the California golden trout (Oncorhynchus mykiss aguabonita), Tulare County, California", 2004; Cordes, et al., 2006; Knapp and Matthews, 1996; Matthews, 1996b; Nielson, et al., 1999; Stephens, et al., 2009)

Contributors

Steve Gallas (author), Radford University, Brenna Hyzy (), Radford University, Karen Powers (editor), Radford University, April Tingle (editor), Radford University, Emily Clark (editor), Radford University, Cari Mcgregor (editor), Radford University, Jacob Vaught (editor), Radford University, Genevieve Barnett (editor), Colorado State University, Galen Burrell (editor), Special Projects.

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

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

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

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

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

food

A substance that provides both nutrients and energy to a living thing.

freshwater

mainly lives in water that is not salty.

insectivore

An animal that eats mainly insects or spiders.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

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.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

seasonal breeding

breeding is confined to a particular season

sexual

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

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

vibrations

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

visual

uses sight to communicate

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

California Department of Fish and Game. Conservation assessment and strategy for the California golden trout (Oncorhynchus mykiss aguabonita), Tulare County, California. none. Sacramento, California: U.S. Fish and Wildlife Service. 2004.

California Trout. Economic value of golden trout fishing in the Golden Trout Wilderness, California. None. San Francisco, California: California Trout (Alkire, C. ). 2003. Accessed April 22, 2015 at http://www.sierraforestlegacy.org/Resources/Conservation/FireForestEcology/ForestEconomics/Golden-Trout-Report-full-report.pdf.

Cordes, J., M. Stephens, M. Blumberg, B. May. 2006. Identifying introgressive hybridization in native populations of California golden trout based on molecular markers. Transactions of the American Fisheries Society, 135/1: 110-128.

Fisk, D., L. Latta, R. Knapp, M. Pfrender. 2007. Rapid evolution in response to introduced predators I: Rates and patterns of morphological and life-history trait divergence. BMC Evolutionary Biology, 7/1: 22.

Grubb, T. 2003. The Mind of the Trout: A Cognitive Ecology for Biologists and Anglers. Madison, Wisconsin: University of Wisconsin Press.

Heckman, R. 1974. Parasites of golden trout from California. The Journal of Parasitology, 60/2: 363.

Knapp, R., T. Dudley. 1990. Growth and longevity of golden trout, Oncorhynchus aguabonita, in their native streams. California Fish and Game, 76/3: 161-173.

Knapp, R., K. Matthews. 1996. Livestock grazing, golden trout, and streams in the Golden Trout Wilderness, California: Implications and management implications. North American Journal of Fisheries Management, 16/4: 805-820.

Knapp, R., H. Preisler. 1999. Is it possible to predict habitat use by spawning salmonids? A test using California golden trout (Oncorhynchus mykiss aguabonita). Canadian Journal of Fisheries and Aquatic Sciences, 56/9: 1576-1584.

Knapp, R., V. Vredenburg. 1996. Spawning by California golden trout: Characteristics of spawning fish, seasonal and daily timing, redd characteristics, and microhabitat preferences. Transactions of American Fisheries Society, 125/4: 519-531.

Knapp, R., V. Vredenburg, K. Matthews. 1998. Effects of stream channel morphology on golden trout spawning. Ecological Applications, 8/4: 1104-1117.

Matthews, K. 1996. Diel movement and habitat use of California golden trout in the Golden Trout Wilderness, California. Transactions of the American Fisheries Society, 125/1: 78-86.

Matthews, K. 1996. Habitat selection and movement patterns of California golden trout in degraded and recovering stream sections of the Golden Trout Wilderness, California. North American Journal of Fisheries Management, 16/3: 579-590.

Nielson, J., K. Crow, M. Fountain. 1999. Microsatellite diversity and conservation of a relic trout population: McCloud River redband trout. Molecular Ecology, 8/1: S129-S142.

Randall, J. 2014. Trout Sense. 5067 Ritter Road, Mechanicsburg, PA, 17055: Stackpole Books.

Stefferud, J. 1993. Spawning season and microhabitat use by California golden trout (Oncorhynchus mykiss aguabonita) in the southern Sierra Nevada. California Fish and Game, 79/4: 133-144.

Stephens, M., N. Clipperton, B. May. 2009. Subspecies-informative SNP assays for evaluating introgression between native golden trout and native rainbow trout. Molecular Ecology Resources, 9/1: 339-343.

Tabor, R. 1991. Predation risk and the importance of cover for juvenile rainbow trout in lentic systems. Transactions of the American Fisheries Society, 120/6: 728-738.

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