The Rainbow Trout’s North American range spans from Alaska to Mexico, including the Great Lakes, British Columbia, and the Eastern United States, but the species can be found as far away as Russia (Bosanko 2007). Many states within the U.S., including Minnesota, stock Rainbow Trout as a non-native game species due to their temperate habitat requirements (Bosanko 2007; Staley & Mueller 2000). Rainbow Trout are found in a variety of places depending on the population, but mostly occupy cool and clear waters in headwater, creek, river, lake, estuary, and oceanic habitats (Staley & Mueller 2000). The ability for Rainbow Trout to move between these different habitats is critical for sustainable populations (Staley & Mueller 2000). Rainbow Trout thrive best in complex environments that house an assortment of submergent and emergent vegetation types, boulders, logs, pools, and riffles (Staley & Mueller 2000). Rainbow Trout are sensitive to pollution, so they require clean waters to survive (Staley & Mueller 2000)

Food:  

Rainbow Trout are opportunistic feeders, mostly feeding on invertebrates such as insects, crayfish, leeches, worms, plankton, and snails, but will also eat small fish and fish eggs (Staley & Mueller 2000). During the early summer, much of a Rainbow Trout’s diet will consist of larval dragonflies, mayflies, and caddisflies (Staley & Mueller 2000). Within the fisheries setting, fry are more often fed an aquafeed that has replaced traditional fishmeal with a plant-based alternative (Michl et al. 2017). This switch has increased microbial gut diversity, leading to more abundant and resilient fry populations (Michl et al. 2017). It has also been observed that fry with increased amounts of gut microbes adapt a resilience to red mouth disease (Michl et al. 2017).

Reproduction:  

Rainbow Trout can spawn anywhere from late winter to early summer, depending on the population and the warmth of the water (Delaney 2008). Rainbow Trout begin spawning between the ages of six and seven years of age, when they reach sexual maturity, however individuals as young as three years of age have been observed spawning (Delaney 2008).  The scale coloration of breeding Rainbow Trout darkens, their bodies going from silver to olive, and their horizontal stripe going from pink to crimson (Delaney 2008). Rainbow Trout spawn in clearwater streams and have even been known to exhibit site fidelity, returning to the locations they themselves hatched from (Staley & Mueller 2000). When partners are ready to spawn, the female digs within the gravel of a riffle, creating a redd (Staley & Mueller 2000). The redd must be constructed at the correct water depth and sediment type or the eggs will not receive proper oxygen (Staley & Mueller 2000) The female deposits 200-8,000 eggs within the redd, where the male then fertilizes them (Staley & Mueller 2000). The eggs are then covered with loose gravel, and the female swims upstream to create another redd, repeating the process (Staley & Mueller 2000). Eggs can take a few weeks to a few months to hatch, and when they do, they remain within the redd until the yolk sacs within their bodies are depleted (Delaney 2008). When the fry are ready to emerge, they do so as a group and feed in areas with large amounts of cover as they do not receive any parental care (Delaney 2008).

Other Interesting Facts:  

Oncorhynchus mykiss aguabonita, commonly referred to as Golden Trout, is a subspecies derived from coastal Rainbow Trout (Needham & Gard 1959). Golden Trout exhibit bright yellow scales that are thought to provide camouflage in their volcanic substrate habitats (Needham & Gard 1959). Golden Trout are  more active during the day than other trout, implying there is some sort of advantage to having this coloration that makes them less likely to be predated upon (Needham & Gard 1959). When individuals are translocated from their native high altitudes to streams in lower altitudes, the coloration of the Golden Trout shifts to silver (Needham & Gard 1959).

Bosanko, D. 2007. Fish of Minnesota Field Guide. Adventure Publications Inc., Cambridge, MN.

Delaney, K. 2008. Rainbow Trout. Alaska Wildlife Notebook Series, Juneau, AK.

Gartner, W., Love, L., Erkkila, D, & Fulton, D. 2002. Economic Impact and Social Benefits Study of Coldwater Angling in Minnesota. University of Minnesota Extension Service, Saint Paul, MN.

Jelks, H.L., Walsh, S.J., Burkhead, N.M., Contreras-Balderas, S., Díaz-Pardo, E., Hendrickson, D.A., Lyons, J., Mandrak, N.E., McCormick, F., Nelson, J.S., Platania, S.P., Porter, B.A., Renaud, C.B., Schmitter-Soto, J.J., Taylor, E.B., Warren, M.L. 2008. Conservation status of imperiled North American freshwater and diadromous fishes. Fisheries 33(8): 372-407.

Michl, S.C., Ratten, J.M., Beyer, M., Hasler, M., Laroche, J., & Schulz, C. 2017. The malleable gut microbiome of juvenile rainbow trout (Oncorhynchus mykiss): Diet-dependent shifts of bacterial community structures. PLoS ONE, 12: 1-21.

Needham, P.R. & Gard, R..1959. Rainbow trout in Mexico and California: with notes on cutthroat the series. University of California. Publ. Zool. 67:1-124.

Root, L. 1994. Rainbow Trout (Oncorhynchus mykiss). South Dakota Game, Fish, & Parks. Rapid City, SD.

Staley, K. & Mueller, J. 2000. Rainbow Trout (Oncorhynchus mykiss). Wildlife Habitat Management Institute Publ., 13: 1-11.

Stearley, R.F. & Smith, G.R. 1993. Phylogeny of the Pacific Trouts and Salmons (Oncorhynchus) and Genera of the Family Salmonidae. Transactions of the American Fisheries Society 122:1-33.

Ward, H. 2014. COSEWIC Assessment and Status Report on the Rainbow Trout. Committee on the Status of Endangered Wildlife in Canada, Ottawa, ON.