ADF&G Home » Species » Animals » Steelhead and Ra inbow Trout Jump to species:

Printer friendly

Description Uses Management Research Get Involved More Resources

Did You Know?
Nearly all of the rainbow and steelhead troutcaught and released by anglers will survive if handled properly.

Description Life History Range and Habitat Status, Trends, and Threats Fast Facts



### General Description Rainbow and steelhea d trout are the most widely known trout in the world and are highly sought after by anglers because of t heir strong fighting abil ities. In Alaska, there are two commonly recognized forms of the rainbo w trout and these sub-groupings or “forms” are based primarily on where they spend thei r time feeding and maturi ng. The most common rai nbow trout in Alaska is the stream-resident fo rm that lives its life enti rely in freshwater with maybe short periods of time spent in estuarine or near-s hore marine waters. The second form is commonly known as steelhead and these rainbow trout leave fr eshwater as juveni les and migrate long distances in the ocean where they grow to maturity before mi grating back to their original home waters.

Since rainbow and steelh ead trout are the same species there are no major physical differences between them, however, the nature of their differi ng lifestyles has resulted in subtle differences in color, shape, size, and general appea rance. Juvenile steelhead are indistinguishable from 

### ( Oncorhynchus mykiss )

Photo Gallery Video View Large Map Steelhead / Rainbow Trout Species Profile, Alaska Department of Fish a... http ://www.adfg.alaska.gov/index.cfm?adfg=steelhead.main

1 of 2 4/20/2016 4:17 PMjuvenile rainbow trout du ring the first few ye ars of their life. Young trout have eight to thirteen parr marks on their sides and fi ve to ten parr marks between the top ofthe head and do rsal fin. The adipose fin usually has a continu ous outline of black su rrounded by a clear wi ndow and the lower jaw (maxillary) typically does not extend past the back ma rgin of the eye. Pr ior to their seaward migration juvenile stee lhead go through a series of physical changes calle d smoltification which allows them to survive in saltwater; during this proce ss the fish lose thei r parr marks and become silvery in color.
Within a year or so of hatchi ng the stream resident form of rainbow trout possess the well-known streamlined salmonid form, tho ugh body shape and co loration vary widely and reflect habitat, age, sex, and degr ee of maturity. The body shape may range from slender to thick. The back may shade from blue-green to olive. There is a reddish-pink band along each side about the midline that may range from faint to radiant. The lower sides are usually silver, fading to pure white beneath. Small black spots are present over the back above the lateral line, as well as on the upper fins and ta il. In some locations, the bl ack spots of adults may ext end well below the lateral line and even cover the entire lo wer side. Rainbow trout are posit ively identified by the 8 to 12 rays in the anal fin, a mouth that does not extend past the back of the eye, and the lack of teeth at the base of the to ngue. River or stream reside nts normally display the most intense pink stripe coloration and heaviest spotti ng followed by rainbows from lake and lake-stream systems. Spawning trout are ch aracterized by general ly darker coloration.
Adult steelhead which have spent 1 to 3 years in the ocean ar e generally heavily spotted with irregularly shaped dark spots bo th above and below the latera l line. Small spots are also scattered along the top ofthe head, along the side s, on the dorsal and bo th lobes of the caudal fins. Steelhead are typically silvery or brassy in color butmay range from steely blue and emerald green to olive. Steelhead fresh fr om the ocean can be ve ry bright and much mo re silver in color than resident rainbo w. The classic band of co lor along the late ral line, which rainbow trout are named for, can range from light pink to deep red with mature males having the brightest colors. Although typically larger in size, steelhead are generally mo re slender and streamlined than stream resident rai nbow trout. On steel head the typical colors and s pots of the trout appear to be coming from beneath a do minant silvery sheen which gradual ly fades in fresh water and steelhead become difficult to diff erentiate from mature resident rainbow trout. The distinct and beautiful coloration of steelhe ad during the freshwater spawning period is important for mating and reproduction while the silvery sheen and streamlined shape of ocean-br ight steelhead is essential to survival in the ocean environment.

Stream resident rainbow trout an d juvenile steelhead ca n usually be distinguish ed from their close relative the cutthroat tr out because rainbow trout do not have t he classic red or “cutthroat” slash on the underside of thei r lower jaw. However not all cutthroat trout have th is slash and there are naturally occurring rainbow/cutthroat trout hybrids which hav e physical markings of both. Biologists often use the presence/absence of small teeth at the base of th e tongue called basibranchial teeth as a means to distinguish between steelhead (teeth absent) and cutthroat trout (teeth present). Steelhead / Rainbow Trout Species Profile, Alaska Department of Fish a... http ://www.adfg.alaska.gov/index.cfm?adfg=steelhead.main

2 of 2 4/20/2016 4:17 PM