My thought is to say, "dude, you can't keep 5 trout now, are you aware of that?"
If it bothered you, you should have opened your mouth. Unless the only way for you is a keyboard. Which is fine, I guess
Some guys know, some don't, some are just hogs. But you should have said something. That local fish guy ain't coming out on Christmas day for that. If there was a guy with a cast net, well that's different.
If the guy says "mind your own business", well get his plate number while he watches you do that.
Concealed carry permits are nice, too. Open carry is legal, which instantly solves issues as well. Ain't too many genuine dirt bags out there will mess with you on a lake or stream with a weapon strapped to you in plain view. But a carry permit allows you to drive the weapon with you in a vehicle. Open carry, no permit, no car. Walk to and fro
And don't post back sissy sarcastic sh*t, I'm being serious.