Rainbow trout or Steelhead as the are often called are a unique fish.  Though genetically the same as stream trout, when they live in Lake Michigan they grow to great proportions.  Commonly thought of as the most exciting fish to catch in the great lakes, they can certainly be a challenge to get into the boat.  They are escape artists with their antics.  Known for high flying jumps with lots of twists and backflips, steelhead are a joy to watch.  Contrary to other fish, steelhead often make their presence known from the getgo with their leaps into the air and thrashing along the surface.  Steelhead are less predictable when fishing for them compared to the salmon.  They can move great distances in a single day and often for no apparent reason.  They are not home bodies.  Steelhead are also palegic and are often caught in the top 10-20 feet of water even though we might be fishing in 300+ feet of water.  Steelhead average 3-7#, however fish in the 10-15# range get caught frequently.  They are very silver in appearance, have small spots on their tails and a subtle rainbow or pink stripe along their sides that shows up better after the fish return to the lake after spawning in the spring.  Being a trout, steelhead do not die after spawning.  Below are a couple pictures showing typical steelhead.

Michigan DNR description:

Steelhead Oncorhynchus mykiss 

Identifying characteristics: (Non-Native Fish) Two dorsal fins including one adipose fin, mouth and gums are light, small spots along rays on entire tail, 10-12 rays in anal fin.

Steelhead is a name given to rainbow trout which live in the Great lakes. Rainbow trout are native to the Pacific Ocean along North America and to rivers and other fresh waters of North America west of the Rocky Mountains. They are a popular game fish, and for this reason have been introduced all over the United States.

Great lakes steelhead are usually found in waters less than 35 feet deep at temperatures of 58-62 degrees F. They are often found near stream outlets, especially in spring and early summer. In the lake-dwelling part of their life cycle, they wander along the shoals eating plankton, minnows, surface and bottom insects and other aquatic life. Although they feed primarily in mid-depths, they do take surface insects, including fly fishermen's flies. Larger rainbows will eat other small fish if available.

Great Lakes steelhead enter their spawning streams from late October to early May. At the present most spawning occurs in the spring, although more steelhead are beginning to spawn in fall. Spawning takes place in a bed of fine gravel, usually in a riffle above a pool. Steelhead don't necessarily die after this; they may live to reproduce for as many as five successive years. Most rainbow trout return home to spawn in the stream in which they were born or planted.

Trout eggs hatch in four to seven weeks, depending on water temperature. Young trout may travel downstream to the lake in their first summer, or they may remain from one to three years in their home stream before migrating lakeward.

Individual growth varies greatly even within the same population. Most Great lakes steelhead reach sexual maturity at age three to five years, ahead of females. A mature 16-inch fish living in the Great lakes may continue to grow throughout its life and could reach 36 inches in length and up to 20 pounds in weight. However, average adult size for steelhead in 9 to 10 pounds while life expectancy in the Great Lakes is six to eight years.

Larger fish, fish-eating birds and mammals and sea lamprey are the steelhead's natural enemies. In turn, the steelhead finds itself competing with other salmon and trout, other predatory fishes and a variety of bottom feeders, for its food. It also competes with salmon and trout for spawning grounds.

Steelhead are valiant fighters and their flesh is outstanding no matter how it is cooked. An unbeatable combination that makes them one of the most popular North American sport fish.