When I was a kid there was a creek near my house that we all went crawfishing in. One winter about a thousand foot-long goldfish miraculously appeared. I guess somebody must have cleaned out their Koi pond.
Personally, if I were that guy I would have released the fish. I certainly wouldn't want a big goldfish hanging on the wall for my buddies to laugh at.
If he wants a mounted fish, then go after the muskies which are getting in the neighborhood of 55" and 50+ lbs in the lake......
Did you happen to lick a frog before you saw this fish?