OK since everyone else is having their own opinion i will have mine.
Dingo released a fish into a body of water that to his knowledge, cant overflow and if it did it would not overflow into any rivers. Amehal0 has tilly's in a pond that to his knowledge cant overflow to any rivers because his drainage is stuffed, i have seen his setups and i agree that the fish would have to be able to jump or fly to get to any river, while dodging traffic. Since you both did illegal activities you guys pretty much cross each other out, i mean your arguing over somthing that the other person has done, yet both of you have done something illegal.
I do not agree with either of you. Releasing "Captive fish" into the wild can cause alot of damage to the enviroment and anything that lives there, even if that body of water was "dammed" off so it can not reach rivers/creeks, it would still cause havoc that would not naturally be there.
As for Amehal0 keeping tilarpia, it is illegal to keep them by law, any fish caught from the wild must be killed and rolled up the bank and buried, your not even aloud to keep the fillets from the fish to take home. But since this was his first fish and it has sentimental value and is in a pond in an enclosed room with no drainage and there is no possible way it can escape to the wild and cause havoc, i dont think it is a big concern. Even though it was illegal in the first place.
Cam