Some trout species are split between those that have the DNA for heading to the Oceans or Large Freshwater Regions, as part of their life cycle, while other trout of the same species, remain in the the same stream or river where they were born. Sea going Brown Trout are commonly called Sea Trout, Sea going Rainbows are commonly called Steelheads, while the Sea going Brook Trout (I include them even though they are not truely Trout related to directly to the Salmon Family) are called Coasters. I really do not know anything more on the subject.