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rainbow trout
Type Locality Columbia River at Fort Vancouver, Vancouver, Washington (Richardson 1836).
Etymology/Derivation of Scientific Name Oncorhynchus: hooked snout; mykiss a vernacular name for the species in Kamchatka, Russia (Ross 2001).
Synonymy Salmo gaidnerii Richardson 1836:221.
Characters Maximum size: 1000 mm TL (Behnke 1980).
Coloration: paired fins with white border; small spots heavily scattered along sides and caudle fin (Hubbs et al 1991).
Counts: 120-140 lateral scale rows (Hubbs et al 1991). There are 100-150 SC, 16-22 gillrakers, 10-12 dorsal rays, 10-11 (8-13) anal rays, 11-17 pectoral rays, and 9-10 pelvic rays (Ross 2001; modified from Scott and Crossman 1973; Robison and Buchanan 1988).
Body shape: Elongate, laterally compressed fish (Ross 2001).
Mouth position: Terminal (Goldstein and Simon 1999). Teeth present on jaws, palantine bones in roof of mouth and tip of tongue; no teeth present on midline of tongue (Robison and Buchanan 1988).
External morphology: Has a single, spineless dorsal fin and an adipose fin. The maxillary seldom extends posteriorly beyond the eye. Small axillary processes are present at the base of the pelvic fins; lateral line is complete (Ross 2001). Breeding males develop a hook on lower jaw (Robison and Buchanan 1988).
Distribution (Native and Introduced) U.S. distribution: Native to streams of the Pacific Northwest from Baja, California to Alaska (Hubbs et al 1991).
Texas distribution: This introduced species has a self-sustaining population only in McKittrick Canyon in the Guadalupe Mountains; introduced individuals may be found in many other localities that provide a “put and take” fishery (Knapp1953; Hubbs et al 1991). Sam Rayburn Reservoir (impounds the Angelina River; Anderson et al. 2002). Texas Parks and Wildlife (2001) lists species records for the following locations: (Data courtesy of the U.S. Geological Survey – USGS home page http://www.usgs.gov). TX - Buffalo Wallow Pond
Abundance/Conservation status (Federal, State, NGO)
Habitat Associations Macrohabitat: Habitats range from small creeks, rivers, lakes, and reservoirs to the open ocean. Sea-run rainbow trout are called steelhead (Ross 2001).
Mesohabitat: Most can grow well at 17-20°C, but they cannot tolerate water temperatures above 28-29°C (Lee and Rinne 1980), and they seem to prefer water temperatures around 11°C (McCauley et al. 1977). Populations introduced in North Carolina inhabit the lower reaches of cool-water streams, shaded pools, runs, and riffles (Larson and Moore 1985; Lohr and West 1992). Fry emerge from gravel 2-3 weeks after hatching and live in quiet waters close to shore (Moyle 1976).
Biology Spawning season: Time of spawning is variable, with introduced populations in the southeast reproducing during the cooler months, from November through February or March (Carlander 1969). During April, in Tennessee, individuals emerge from redds suggesting that spawning occurs in March (Whitworth and Strange 1983). In New York, spawning occurs late spring or summer (Johnson and Ringler 1981). In California, wild rainbow trout spawn in the spring from February to June; low temperatures in high mountain areas may delay spawning until July or August (Moyle 1976).
Spawning location: Lithophils, rock and gravel spawners that do not guard their eggs (Simon 1999).Generally spawning occurs in streams, rather than lake habitats, with fertilized eggs buried in the gravel of the redd (Carlander 1969; Tautz and Groot 1975; Newcombe and Hartman 1980).
Reproductive strategy: Nonguarders; brood hiders (Simon 1999). With the male hovering above, chasing away intruders, the female excavates a redd. After she completed the nest, the female signals the male to initiate spawning (Tautz and Groot 1975; Newcombe and Hartman 1980). After spawning is complete, the redd is no longer defended (Carlander 1969).
Fecundity: Rainbow trout usually spawn once a year; fish may skip a year between spawnings. Number of eggs laid per female ranges from 200-12,000 eggs, depending on size and origin of the fish. Fish under 30 cm TL typically contain less than 1,000 eggs. Eggs hatch in 3-4 weeks at water temperature of 10-15 degrees C (Moyle 1976)
Age at maturation: Highly variable, and is influenced by growth rates and whether or not the population is migratory (Ross 2001). Nonandromous rainbow trout mature in their 2nd or 3rd year, but time of first maturity can vary from the 1st-5th year of life (Moyle1976).
Migration: Andromous populations (like Pacific coastal O. mykiss, called steelheads) occupy coastal streams. Resident nonmigratory populations are found farther inland (Robison and Buchanan 1988).
Longevity: 11 years (Carlander 1969). Trout in landlocked streams rarely live longer than 3 or 4 years (Northcote 1981; Whitworth and Strange 1983).
Growth: In Tennessee, rainbow trout measured 104 mm TL at one year, and 186 mm TL by their second year (Whitworth and Strange 1983). Moyle (1976) notes variability of growth rates in rainbow trout: In mountain lakes fish reach 11-17 cm TL in their first year, 14-21 cm TL in their second 20-23 cm TL in their third; seldom living longer than 6 years or growing over 40 cm TL. Growth rates are similar in small California streams. In California, most rapid growth is achieved in large lakes and reservoirs with trout in one lake population measuring 20-23 cm TL at one year old, 43-46 cm TL at two years old, and 46-56 cm TL at three years old; similar growth achieved by fish planted in some reservoirs, but generally somewhat slower, especially after first year.
Food habits: Invertivore/carnivore feeding on invertebrates, other fish, and fish eggs (Goldstein and Simon 1999). Diet includes wide variety of foods, depending upon body size and habitat. Caddisflies, stoneflies, mayflies, and crane flies are important foods for fish inhabiting small streams, as well as large items including crayfishes, salamanders, and frogs. Terrestrial prey consumed include: earthworms, beetles, butterflies, moths, bees, and wasps, and may constitute almost half of diet (Needham 1969; Johnson 1981; Cada et al. 1987). Daphnids may also be major food item in lake populations, though rainbow trout are size selective, feeding only on prey in excess of 1.3 mm (Galbraith 1967). Species will feed in a stream while maintaining position in current velocities of 13-21 cm/s. Feeding habitat is based largely on prey capture success (Hill and Grossman 1993). Dominant hierarchy among resident fish will determine the division of feeding stations in a stream; these being defended (Jenkins 1969). Individuals weighing in excess of 1-2 kg usually feed primarily at night and take large prey such as fishes (Needham 1969). Smaller rainbow trout (less than 90 mm, 12 g) tend to be inactive at night (Hill and Grossman 1993). A study of rainbow trout in the Guadalupe River tailwater below Canyon Reservoir, Texas, found this species to actively pursue drift prey of baetids, chironomid pupae, and helicopsychid adults. Drift declined during summer months and foraging efforts appeared to be concentrated on the benthos, with ephemerids and pleurocerid snails abundant in diet (Halloran 2000).
Phylogeny and morphologically similar fishes Oncorhynchus mykiss differ from Salmo trutta, the brown trout, in having dark spots on caudal fin and sides without orange or red spots in life. O. mykiss differ from O. clarki, the cutthroat trout, in having fewer than 150 lateral line scales, no teeth on midline of tongue, and no red cutthroat mark (Robison and Buchanan 1988).
Host Records Trematoda (4), Cestoda (1), Nematoda (1), Acanthocephala (3), Crustacea (1) (Hoffman 1967; listed as Salmo mykiss).
Commercial or Environmental Importance
References Anderson, D.K., R.B. Ditton, and C. Oh. 2002. Characteristics, participation patterns, management preferences, expenditures, and economic impacts of Sam Rayburn Reservoir anglers. Report to the Inland Fisheries Division, Texas Parks and Wildlife. Texas Agricultural Experiment Station, Texas A&M University System, College Station. 142 pp. Behnke, R.J. 1980. Salmo gairdneri (Richardson), Rainbow trout. pp. 106 in D.S. Lee et al. Atlas of North American Freshwater Fishes. N.C. State Mus. Nat. Hist., Raleigh, i-r+854 pp. Cada, G. F., J. M. Loar, and M. J. Sale. 1987. Evidence of food limitation of rainbow and brown trout in southern Appalachain soft-water stream. Trans. Amer. Fish. Soc. 116(5):692-702. Carlander, K. D. 1969. Handbook of Freshwater Fishery Biology. Ames, The Iowa State University Press 476 pp. Galbraith, M.G., Jr. 1967. Size-selective predation on Daphnia by rainbow trout and yellow perch. Trans. Amer. Fish. Soc. 96(1):1-10. Goldstein, R.M., and T.P. Simon. 1999. Toward a united definition of guild structure for feeding ecology of North American freshwater fishes. pp. 123-202 in T.P. Simon, editor. Assessing the sustainability and biological integrity of water resources using fish communities. CRC Press, Boca Raton, Florida. Halloran, B.T. 2000. Foraging of introduced rainbow trout Oncorhynchus mykiss in relation to benthic macroinvertebrates and drift in the Guadalupe River tailwater below Canyon Reservoir, TX. Master of Science Thesis. Southwest Texas State University, San Marcos, Texas. 59 pp. Hill, J., and G. D. Grossman. 1993. An energetic model of microhabitat use for rainbow trout and rosyside dace. Ecology 74(3):685-698.
Hoffman, G. L. 1967. Parasites of North American Freshwater Fishes. University of California Press, Berkeley, 486 pp. Hubbs, C., R. J. Edwards, and G. P. Garrett. 1991. An annotated checklist of the freshwater fishes of Texas, with keys to identification of species. Texas Journal of Science, Supplement 43(4):1-56. Jenkins, T. M., Jr. 1969. Social structure, position choice and microdistribution of two trout species (Salmo trutta and Salmo gairdneri) resident in mountain streams. Anim. Behav. Monogr. 2(2):56-123. Johnson, J. H. 1981. Food interrelationships of coexisting brook trout, brown trout and yearling rainbow trout in tributaries of the Salmon River, New York. New York Fish and Game J. 28(1):88-99. Johnson, J.H., and N.H. Ringler. 1981. Natural reproduction and juvenile ecology of Pacific salmon and rainbow trout in tributaries of the Salmon River, New York. New York Fish and Game J. 28(1):49-59. Knapp, F.T. 1953. Fishes found in the freshwater of Texas. Ragland Studio and Litho Printing Co., Brunswick. 166 pp. Larson, G.L., and S.E. Moore. 1985. Encroachment of exotic rainbow trout into stream populations of native brook trout in the southern Appalachian Mountains. Trans. Amer. Fish. Soc. 114:195-203. Lee, R. M., and J. N. Rinne. 1980. Critical thermal maxima of five trout species in the southwestern United States. Trans. Amer. Fish. Soc. 109(6):632-635. Lohr, S.C., and J.L. West. 1992. Microhabitat selection by brook and rainbow trout in a southern Appalachian stream. Trans. Amer. Fish. Soc. 121(6):729-736. McCauley, R. W., J. R. Elliott, and L. A. A. Read. 1977. Influence of acclimation temperature of preferred temperature in the rainbow trout Salmo gairdneri. Trans. Amer. Fish. Soc. 106(4):362-365. Moyle, P.B. 1976. Inland Fishes of California. University of California Press, Berkeley. 405 pp. Needham, P. R. 1969. Trout streams. Holden-Day, San Francisco, California. 241 pp. Newcombe, C.P., and G.F. Hartman.1980.Visual signals in the spawning behavior of rainbow trout. Can. J. Zool. 58(10):1751-1757. Northcote, T. G. 1981. Juvenile current response, growth and maturity above and below waterfall stocks of rainbow trout, Salmo gairdneri. J. Fish Biol. 18:741-751. Richardson, J. 1836. Fauna Boreali-Americana; or the zoology of the northern parts of British America. Pt. 3. The Fish. Richard Bentley, London. Robison, H. W. and T. M. Buchanan. 1988. Fishes of Arkansas. Univ. Arkansas Press, Fayetteville. 536 pp. Ross, S. T. 2001. The Inland Fishes of Mississippi. University Press of Mississippi, Jackson. 624 pp. Scott, W. and E. Crossman. 1973. Freshwater Fishes of Canada. Fish. Res. Bd. Can., Bull. 185:1- 966. Simon, T. P. 1999. Assessment of Balon’s reproductive guilds with application to Midwestern North American Freshwater Fishes, pp. 97-121. In: Simon, T.L. (ed.). Assessing the sustainability and biological integrity of water resources using fish communities. CRC Press. Boca Raton, Florida. 671 pp. Tautz, A. F., and C. Groot. 1975. Spawning behavior of chum salmon (Oncorhynchus keta) and rainbow trout (Salmo gairdneri). J. Fish. Red. Bd. Can. 32:633-642.
Texas Parks and Wildlife Department. 2001. Fish Records: Water Body - All Tackle. Texas Parks and Wildlife Department. April 24, 2001 Whitworth, W. E., and R. J. Strange. 1983. Growth and production of sympatric brook and rainbow trout in an Appalachian stream. Trans. Amer. Fish. Soc. 112(4):469-475.
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