Rainbow trout (Oncorhynchus)
The elongated, streamlined body of the rainbow trout is typical of all trout, although shape and coloration vary widely depending on habitat, age, and sex. The body shape may also range from slender to thick depending on diet. Coloring may be blue-green to olive with a distinctive reddish pink band along each side, which will vary in brightness. The lower sides are usually silver, fading to white at the belly.
Small black spots are present above and along the lateral line, as well as on the upper fins and tail. On some rainbows, these black spots may cover the entire lower side. Rainbow trout are distinguished from salmon and other trout species by the 8 to 12 rays in the anal fin, a mouth that does not extend past the eye, and no teeth at the base of the tongue.
Coloration varies with size, habitat and season. Stream-dwelling rainbows usually have darker, more brilliant coloring than those found in other waters. River or stream rainbows also possess a brighter pink stripe and more prominent spots, followed by rainbows from lake and lake-stream systems. Conversely, rainbows that migrate to the ocean or Great Lakes (steelhead) will take on a more silver appearance and may not have a pink stripe along the middle of its sides.
In many cases, a rainbows coloring also depends on whether the fish was raised in a hatchery or born naturally in a lake, river or stream. Hatchery fish, in general, will not display the brilliant color markings found on wild fish. However, if a stocked fish survives for several years in a body of water, it will often display stronger colors.
Rainbow trout are opportunistic feeders. Their diet is highly variable, with some fish seemingly taking nearly any living thing that drifts or swims by, as long as its small enough to engulf. In most cases, a given body of water will provide one or two staples of the rainbows diet, primarily insects or baitfish.
The bulk of their diet is comprised of mayflies, caddis flies, stoneflies and their larvae, small mollusks and baitfish. Fish eggs are another favorite food, particularly when rainbow trout share a stream with migrating salmon, as well as during their own spawning cycles. In large lakes, big rainbow trout feed mainly on baitfish, such as alewives, sculpins or smelt.
Rainbow trout are native only to the West Coast of North America, spanning from southern Alaska to northern Mexico, and inland as far as Alberta, Canada, Idaho and Nevada. Due to extensive stocking, the range of the rainbow trout has been extended across the lower Canadian provinces, throughout the Great Lakes region and northeastern United States, all the way to the Atlantic Coast and south through the Appalachians to northern Georgia and Alabama. Rainbows have also been introduced throughout the western United States, as well as selected waters in the Midwest and South.
Rainbow trout have also been introduced to colder waters in New Zealand, Australia, South America, Africa, Japan, southern Asia, Europe, and Hawaii. In these areas, stocking has only been successful at elevations of 4,000 feet or more.
Rainbow trout prefer cold-water streams with gravel or rocky bottoms, deep pools, and natural cover. They also thrive in large lakes with cool, deep waters. Though the temperature tolerance of rainbow trout is from 32 F to over 70 F, their ideal temperature range is between 55 and 60 F. They are found in fast moving water, often at the head of rapids or strong riffles, under vegetation and around rocks, fallen trees, or other structures.
Stocked rainbow trout can adapt well to virtually any waters in its preferred temperature range, but they need proper habitat, year-round ideal temperatures, and food sources for long-term survival.
- Steelhead trout are considered by scientists to be biologically identical to rainbow trout. The only difference is that steelhead are anadromous, living part of their lives in the ocean and returning to freshwater streams to spawn.
- Rainbow trout are hardy, adaptable fish that live in a variety of habitats. They are thus popular among hatchery managers and are frequently stocked.
- Ten of the top 15 world-record rainbow trout have been caught in Lake Michigan.