A few winters ago I was @ work before having to go to class and and I was listening to the news on my route truck radio... the news came on and some guy in Minnesota had caught a Piranha while Ice fishing... And it had weighed POUNDS!!!
We have a few farm ponds on our properties and friends also have farm ponds. Our tank fish come from these ponds and get placed back from time to time. While I understand and agree with the sentiment here, a little common sense goes a long way. I worry more about introducing something to my tanks than introducing something into the pond.
So, for the most part I understand but, there are exceptions to the rule.