The rainbow trout, known scientifically as Oncorhynchus mykiss, is a coldwater fish that is found throughout the Northern Hemisphere in freshwater streams and lakes and in the ocean. They are commonly referred to by many other names, including rainbow, bow, steelhead trout, Kamloops trout and silver trout depending on their coloration and location.

Description

The rainbow trout is about 16 to 30 inches in length and can weigh between 2 and 16 pounds. Their bodies are elongated and slightly compressed, with a squared tail. Their anal rays contain twelve or less rays and the inside of the mouth is white. They are named for their color, which can be variable. The coloration of each fish can also change throughout the year, especially during spawning season. The back is usually darker and the shading can range from a steel blue or green to brown. The cheeks and sides are silvery and they sometimes have a pink or red lateral stripe. The belly of the fish is silvery white. The body is covered in spots.

Subspecies

Six native subspecies of rainbow trout are found in the Pacific Ocean and western United States. These are the Columbia River red band trout, California golden trout, Kern & Little Kern golden trout, Sacramento red band trout, Coastal rainbow trout and Kamchatkan rainbow trout.

Range

Rainbow trout have been introduced on every continent except Antarctica, but their native habitat is the cooler waters of the northern hemisphere, specifically the North American Pacific Coast from Mexico to the Bering Sea, the Pacific Ocean and Asia's eastern coast.

Reproduction

Rainbow trout begin breeding between the ages of 1 and 5 years, with males maturing faster than females. The fish spawn upstream and can travel quite a distance to find a desirable location. In the spring, the female trout create a nest, called a redd. The eggs hatch in July. Unlike salmon, trout do not die after spawning. Some varieties have been developed, through selective breeding, to have different spawning seasons and these may breed in the fall or winter.

Diet

Rainbow trout are carnivores. The primary diet for a young rainbow trout is insects and crustaceans. Adult trout eat other fish, including other trout. When the desired foods are not available, the trout will turn to such foods like insect larvae and pupae. They will also eat worms and even salamanders. Rainbow trout will travel to search for food, when necessary.

Life Cycle

-- The Egg: Healthy trout eggs have a black eye and a central line. They hatch when the water reaches the appropriate temperature.

-- Alevin: After hatching, the baby trout consume the yolk sac. They live near the gravel while they begin to develop the characteristics of adult trout.

-- Fry: After the alevin finish the yolk sac, they move on to zooplankton. At this point they swim close to the surface of the water to fill the swim bladder with air, which helps the young fish float.

-- Fingerling and Parr: Once fry reach a size of about 2 to 5 inches, they are referred to as a "fingerling." It becomes a parr once it develops its dark markings.

-- Juvenile: A juvenile trout is one that resembles an adult trout, but has not yet reached spawning age or size.

-- Adult: The fish is now ready to spawn. During spawning season the trout's coloration becomes vibrant and eggs are deposited into the redds.

Sources:

Fishes of Minnesota: Rainbow Trout. Minnesota Department of Natural Resources. 2011. http://www.dnr.state.mn.us/fish/rainbowtrout.html

The Life Cycle of Rainbow Trout. Nevada Division of Wildlife. http://www.ndow.org/learn/tic/tic.pdf

Rainbow Trout. Wisconsin Department of Natural Resource, Bureau of Fisheries Management. February 2008. http://dnr.wi.gov/fish/pubs/rainbowtrout.pdf

Rengstorf, Santiago. The Biogeography of Rainbow Trout (Oncorhyncus mykiss). San Francisco State University Department of Geography. September 2005. http://bss.sfsu.edu/holzman/courses/fall01%20projects/rainbow%20trout.htm