Editing Rainbow trout (section)

===Steelhead life cycle===
{{see also|Salmon run|Steelhead}}
The oceangoing (anadromous) form, including those returning for spawning, are known as steelhead in Canada and the U.S.<ref>{{cite web|publisher=Alaska Department of Fish and Game|title=Steelhead/Rainbow Trout Species Profile|url=http://www.adfg.alaska.gov/index.cfm?adfg=steelhead.main|access-date=2013-08-26}}</ref> In [[Tasmania]] they are commercially propagated in [[Aquaculture of salmonids#Sea cages|sea cages]] and are known as '''ocean trout''', although they are the same species.<ref>{{cite web |url=http://www.mesa.edu.au/aquaculture/aquaculture14.asp |title=Mariculture in Tasmania Ocean Trout |publisher=Marine Education Association of Australasia |access-date=2014-02-23}}</ref>

Like salmon, steelhead return to their original hatching grounds to [[Spawn (biology)|spawn]]. Similar to Atlantic salmon, but unlike their Pacific ''Oncorhynchus'' salmonid kin, steelhead are [[Semelparity and iteroparity|iteroparous]] (able to spawn several times, each time separated by months) and make several spawning trips between fresh and salt water, although fewer than 10&nbsp;percent of native spawning adults survive from one spawning to another.<ref name=Behnke2002-70>{{cite book |last=Behnke |first=Robert J. |others=Tomelleri, Joseph R. (illustrator) |title=Trout and Salmon of North America |publisher=The Free Press|location=New York |isbn=978-0-7432-2220-4 |year=2002 |page=70 |chapter=Rainbow and Redband Trout }}</ref> The survival rate for introduced populations in the Great Lakes is as high as 70&nbsp;percent. As young steelhead transition from freshwater to saltwater, a process called "[[smoltification]]" occurs where the trout undergoes physiological changes to allow it to survive in seawater.<ref name="Nichols2008">{{cite journal |title=The Genetic Basis of Smoltification-Related Traits in ''Oncorhynchus mykiss'' |journal=Genetics |volume=179 |number=3 |date=July 2008 |author1=Nichols, Krista M. |author2=Edo, Alicia Felip |author3=Wheeler, Paul A. |author4=Thorgaard, Gary H. |pages=1559–1575 |doi=10.1534/genetics.107.084251 |pmc=2475755 |pmid=18562654}}</ref> There are genetic differences between freshwater and steelhead populations that may account for the smoltification in steelhead.<ref>{{Cite journal | last1=Hale | first1=MC | last2=Thrower | first2=FP | last3=Berntson | first3=EA | last4=Miller | first4=MR | last5=Nichols | first5=KM | title=Evaluating Adaptive Divergence Between Migratory and Nonmigratory Ecotypes of a Salmonid Fish, ''Oncorhynchus mykiss'' | journal=G3: Genes, Genomes, Genetics | volume=3 | issue=8 | pages=1273–1285 |date=August 2013 | doi=10.1534/g3.113.006817 | pmid=23797103 | pmc=3737167 }}</ref>

Juvenile steelhead may remain in the river for one to three years before smolting and migrating to sea. Individual steelhead populations leave the ocean and [[Fish migration|migrate]] into their freshwater spawning tributaries at different times of the year. Two general forms exist—"summer-run steelhead" and "winter-run steelhead". Summer-run fish leave the ocean between May and October before their reproductive organs are fully mature. They mature in freshwater while en route to spawning grounds where they spawn in the spring. Summer-run fish generally spawn in longer, more inland rivers such as the Columbia River. Winter-run fish are ready to spawn when they leave the ocean, typically between November and April, and spawn shortly after returning to fresh water. Winter-run fish generally spawn in shorter, coastal rivers typically found along the [[Olympic Peninsula]] and British Columbia coastline,<ref name=Behnke2002-68/> and summer-run fish are found in some shorter, coastal streams.<ref>{{cite web |url=http://wdfw.wa.gov/fishing/salmon/steelhead.html |title=Recreational Salmon Fishing Salmon/Steelhead Species Information Steelhead (Rainbow Trout) ''Oncorhynchus mykiss'' |publisher=Washington Department of Fish and Wildlife |access-date=2014-01-07 |archive-url=https://web.archive.org/web/20140107172404/http://wdfw.wa.gov/fishing/salmon/steelhead.html |archive-date=2014-01-07 |url-status=dead }}</ref> Once steelhead enter riverine systems and reach suitable spawning grounds, they spawn just like resident freshwater rainbow trout.<ref name=Behnke2002-68>{{cite book |last=Behnke |first=Robert J. |others=Tomelleri, Joseph R. (illustrator) |title=Trout and Salmon of North America |publisher=The Free Press|location=New York |isbn=978-0-7432-2220-4 |year=2002 |pages=68–72 |chapter=Rainbow and Redband Trout }}</ref>