Let's all take a deep breath:
In florida, the law is that if you catch a Non-native, you are not allowed to put it back into any body of water. With restricted fish, like Claria and SH, you HAVE to kill them. There are severe penalties for possessing live ones.
So the only options are adoption, or death. If you catch a Pleco, you cannot put it back. It is illegal.
As far as harming the ecosystem.... I don't know.
Since we are talking about man-made lakes and canals here, what is so natural anyway? Most of these lakes in communities are man made, and were stocked arbitrarily anyway.
Pbass were introduced in the 80's, and so they are considered "gamefish". But Oscars have been around a lot longer, and are considered "Invasive".
I don't think there is a clear line here. The best bet is to stick to what the law says, and not get into trouble.