If I may interject some.
Larry is correct about various strains.
Some are caused by isolation from other strains, some by man caused selection of traits, but all are steelhead that never made it to the ocean in time. If they migrate too late and don't make it in time (normally about a year) then their kidneys can't filter out the excess salt and they die. If they make it, they can and will migrate from salt to fresh to spawn several times. Redbands are closely related to Rainbows, even looking like them, but are more closely related to the Cutthroat trout. Cutthroat trout are related to Rainbows and Steelhead, and some Cutties do have a salt water cycle as well. All this is learned while living in the Pacific Northwest where trout, salmon and steelhead are king.
Steelhead in the Great Lakes are NO LONGER STEELHEAD. No salt, no steelhead! But, did you know that if their young can make it to the salt, like any Rainbow strain, they will be Steelhead again? YEP.
There are genetic test, electrophoresis if I recall the spelling, that can identify the strains and can tell one strain of fish from another, so yes, you could tell from the "Steelhead" and the "Rainbow Trout", but, again, the only difference is the source of the strain.
Almost all Washington State "Rainbows" can trace back to some Steelhead strain. The state has also found that most Steelhead "hens" seem to be fertilized by the resident Rainbow "bucks", not the Steelhead strain in the river. A movement is taking place to eradicate rainbow residents to make the Steelhead hens wait for the Steelhead bucks.
Nature is weird, very weird.