I didn't used to know either.
You can read all through the fishing rules for this state and never see anything that says "Don't release fish back into the wild" (Other than referring to storebought bait). The part that mentions it isn't in the fishing rules, it's in the rules about keeping captive animals, which is mostly about mammals, birds and reptiles. I wouldn't have even found it without specifically going and looking for it after hearing on message boards that it's not ok to release fish whether they're native or not.
Even then, the way the rules are written they're kind of confusing. It doesn't specifically say in big letters "DON'T RELEASE NATIVE FISH BACK TO THE WILD", there's all kinds of confusing sections about stuff that seems non-related to what you're looking for but actually is if you read the subsections.
If most states write their rules like my state it's no wonder people don't know this, lol. Combine that with the fact that most people aren't going to understand the possible ecological impact unless it's clearly explained to them in a way that makes it make sense to them and most people just aren't going to get it.