look at that tail! Not sure I'd have the heart to kill it even though its probably maxed out and eating anything and everything it wants.
Taxi- how much bigger do you think it could realize if left to swim?
Hard to say. I've heard of exceptional browns getting to about 40 inches in other parts of the world. OTOH could have been close to the end of it's life span?
Ironically if a trout grows too fast it shortens it's lifespan. I've been told by one biologist the key to longer lifespan in salmonids is access to really cold water even if they don't grown exceptionally fast.
If that river was planted with 8 to 10 inch trout I'll bet they were a big part of it's diet.