Same in Idaho. If fish are not purchased by legal means and are just captured and released in a private pond they don’t become privately owned fish. They were stolen from public waters. That’s called illegal possession here in Idaho. I don’t know about anywhere else outside of Washington, Oregon, Montana and Wyoming. That law applies in those states. Just call the local authorities and they can give you the current laws regarding these kinds of things in your area. If a wild game animal crosses my property and I shoot it out of season or without an appropriate license and tag for my area I’m in violation of the game laws of my state. It’s not mine, I didn’t buy it and there’s no trespass charges against wild animals here. It’s my responsibility to fence it out here as in most states.