Although closely related to salmon, steelhead trout are actually ocean-going forms of rainbow trout. Like salmon, steelhead trout return to their original place of birth from the ocean to spawn once. Unlike salmon, the steelhead trout's physiology allows them to survive the spawning process and return to the ocean. Assuming the steelhead trout are able to survive predation and other pressures, they return to the same area to spawn several times during their lifetime.
Both steelhead trout and salmon go through a physiological transformation, known as smoltification, to survive the process of returning to freshwater from the ocean. During the spawning season, the steelhead trout's smoltification causes the male's skin color to change to a from a highly reflective silver to a darker pattern with red covering a good percent of their body. The salmon's smoltification during the spawning season is much more dramatic. Depending upon the species, salmon can develop a neck hump, a deformation to their jaw and canine teeth for fighting in the spawning grounds.
The spawning process of steelhead trout and salmon, commonly known as a salmon run, is one of the most astonishing journeys undertaken in the animal kingdom, with some animals having to travel hundreds of miles through rapids and waterfalls to reach their spawning grounds. The runs are also crucial to the welfare of the areas in which they occur because they provide predators and scavengers with a critical food source. For example, many populations of grizzly bears are completely dependent on the calories obtained from salmon fat to survive.