IMO fish in streams should be regulated regardless if you are fishing on private property or not. I think a stream running through a persons property is entirely different than a pond located solely on private property.

However if a person builds a pond on his property, buys fish to stock it with his own money, I just can't see any logical argument for the state to regulate those fish.

I don't have a pond, and I doubt I ever will so really I don't have a horse in this race but I do find it interesting and it doesn't make any sense to me. I would love to hear the reasoning behind it. Even if a person chose to mismanage their personal investment, what business is it of the state? Those fish wouldn't even exist without the persons money and efforts.

Ironically I assume the land owner could legally choose to fill in the pond which would kill all the fish, but he couldn't cull out a fish one inch smaller than the legal limit. That's where the entire logic goes right out the window.