Rainbow trout are freshwater fish with a mild, delicate flavor. Rainbow trout are found in many lakes across the U.S. The fillet's color changes based on what they eat. Steelhead Trout are freshwater fish that migrate to the ocean. They taste very similar to salmon. According to A-Z Animals, one of the main differences is that the Atlantic salmon can grow up to 5 times larger than Steelhead trout.