There are intentional introductions. I raised this earlier. I definitely remember a time when someone was going to block boat transport to a lake, and someone made an anonymous call. It was a washing station where they were going to require people to wash their boats, and someone said, “If you do that, I'm just going to dump zebra mussels in the lake and get it over with”.
I'm not sure how to provide live fish without that risk. Maybe they can't take them out live, but I could see somebody saying, “Well, we'll put a few in the bay, and we'll have our own population forever”.