One of the most distinguishing characteristics between steelhead and salmon is the steelhead’s glistening pink stripe that runs from its gills to its sides. However, not all steelheads have this mark, so a fish without a pink line isn’t necessarily a salmon. Another way to tell the difference between steelheads and salmon is to open their mouths. Pacific salmon have dark or black gums. In contrast, steelheads have white gums.