Met as in Methow, Metolius or Seattle Metropolitan Theatre?
If it's the Met"olius" I'd vote for a lake run rainbow that came up the river. If it's the Met"how" I'd vote for a travelling triploid. If its the Seattle Met"ropolitan Theatre" I'd vote for a trout that likes plays.
What's the justification for calling this a trip? The fact that it's chunky? Also, rufus woods triploids do have adipose fins, but none of the fins generally look that good. Looks probably wild or perhaps a diploid plant from an adjacent waterway to me. I would guess that fish hasn't spent it's whole life in that river. It could have come up from Pateros. I don't think I've really seen too many pure rainbows in the Methow. There are a few rare surprises in that river, though, so I don't think it's impossible to grow a rainbow that big in there. Also, it looks like it could be male, which rules out triploid.
Definitely a trip. I've caught them in there before, and it's becoming a pretty regular occurrence to catch them. They're getting through/over Chief Joseph with regularity now. It's how so many end up in Lake Pateros and they open that section up for fishing for them.