it might sound cruel, but its a sensible thing to do. but to put you at peace, if you were to release it again, i dont think it would make an awful lot of difference, the fish are in large populations and have taken a real hold in some areas. however, if it was me, it is the best thing for your environment. introduced species are never a good thing, and it helps protect your NATIVE wildlife...
or dont fish for them lol...
or dont fish for them lol...