The rainbow trout (Oncorhynchus mykiss) is a trout and species of salmonid native to cold-water tributaries of the Pacific Ocean in Asia and North Amercia.
The steelhead is an anadromous form of the coastal rainbow trout, or Columbia River redband trout, which usually returns to fresh water to spawn after living two to three years in the ocean.
Freshwater forms that have been introduced into the Great Lakes and migrate into tributaries to spawn are also called steelhead.
Adult freshwater stream rainbow trout average from 1 to 5 pounds, while lake-dwelling and anadromous forms may reach 20 pounds. They reached 10-15 inches in size.
Adult freshwater forms are generally blue-green or olive green with heavy black spotting over the length of the body. Adult fish have a broad reddish stripe along the lateral line which is most pronounced in breeding males.
The caudal fin is squarish and only mildly forked. Lake-dwelling and anadromous forms are usually more silvery in color with the reddish stripe almost completely gone.
Juvenile rainbow trout display parr marks (dark vertical bars) typical of most salmonid (O. m. gairdneri) populations and cutbow hybrids may also display reddish or pink throat markings similar to cutthroat trout.
In many regions, hatchery-bred trout can be distinguished from native trout via fin clips. Fin clipping the adipose fin is a management tool used to identify hatchery-reared fish.
Rainbow trout, including steelhead forms, generally spawn in early to late spring (January to June in the Northern Hemisphere, and September to November in the Southern Hemisphere) when water temperatures reach at least 42-44 degrees F. The maximum recorded lifespan for a rainbow trout is 11 years.
Freshwater resident rainbow trout usually inhabit and spawn in small to moderately large, well-oxygenated, shallow rivers with gravel bottoms. They are native to the alluvial or freestone streams that are typical tributaries of the Pacific basin, but introduced rainbow trout have established wild, self-sustaining populations in other river types such as bedrock and spring creeks.
Spawning sites are usually a bed of fine gravel in a riffle above a pool. A female trout clears a spot in the gravel by turning on her side and beating her tail up and down.
Female rainbow trout usually produce 2,000 to 3,000 4-to 5-millimetre (0.16 to 0.20 in) eggs per kilogram of weight. During spawning, the eggs fall into spaces between the gravel, and immediately the female begins digging at the upstream edge of the nest, covering the eggs with the displaced gravel.
As eggs are released by the female, a male moves alongside and deposits milt (sperm) over the eggs to fertilize them. The eggs usually hatch in about four to seven weeks, although the time of hatching varies greatly with region and habitat.
Newly-hatched trout are called sac fry or alevin. In approximately two weeks, the yolk sac is completely consumed and fry commence feeding mainly on zooplankton.
The growth rate of rainbow trout is variable with area, habitat, life history, quality and quantity of food. As fry grow, they begin to develop “parr” marks or dark vertical bars on their sides. In this juvenile stage, immature trout are often called “parr” because of the marks.
These small juvenile trout are sometimes called fingerlings because they are approximately the size of a human finger. In streams where rainbow trout are stocked for sport fishing but no natural reproduction occurs, some of the stocked trout may survive and grow or “carryover” for several seasons before they are caught or perish.
Rainbow trout are predators with a varied diet and will eat nearly anything they can capture. They are not as piscivorous or aggressive as brown trout or chars.
They also eat fish eggs and adult forms of terrestrial insects (typically ants, beetles, grasshoppers and crickets) that fall into the water. Other prey include small fish up to one-third of their length, crayfish, shrimp, and other crustaceans.
In Missouri, there are more than 200 kinds of fish, more than are found in most neighboring states. Rainbow trout require waters that are constantly below 70 degrees F, so they are limited to Ozark spring branches, spring-fed streams and Lake Taneycomo, where cold water is discharged from the lower levels of Table Rock Reservoir just upstream.
The Missouri Department of Conservation operates trout hatcheries in order to stock them as game fish in this state. Where trout have established self-sustaining populations, creel and size limits help keep those populations healthy.
Wild trout in Ozark springs spawn in late December through early February; hatchery brood stock spawn in October and November. Hatchery-raised trout grow faster than those in the wild, reaching 10 inches their first year.
With many different types of fish species in Missouri, there are plenty to choose from to enjoy fishing in our great outdoors.
Dana Sturgeon lives in southern Missouri. She can be reached at email@example.com.