Rainbow vs Steelhead, my point was the difference is statutory. There are rivers on the Pacific coast that have or had significant runs of sera run rainbows that commonly were 3lbs or less. Steelhead 'jacks' weren't unknown - I have seen them on the Squamish system.
In close to 60 years of fishing for trout on the Fraser, I have never caught a rainbow other than a few steelhead. Same story for the Harrison. I can think of 2 from that river, one was about 11 inches and had no adipose fin - clearly a residualized hatchery fish (common on the V/C). The other was this monstrosity:
which I thought was an escapee from an illegal private pond. When I sent him a picture the regional biologist thought it came out of Eroch Lake. Some other anglers who have been around the same waters as long as me claim to catch 'rainbows' frequently. But are they rainbows? Cutthroat and rainbows can be very hard to differentiate. Or do I sometimes make a similar mistake in reverse? In spawning colors male cutthroat can take a good rainbow blush on their gill plates and flanks.
My guess is that your fish is more like 18 inches or more. Pretty close to steelhead size.