I grew up fishing in SW
almost exclusively. Its kinda strange, but there's a disconnect when it comes to dealing with food fish and when it comes to dealing with pet fish. The only time it gets weird for me is when I'm collecting natives and I catch a monster bluegill or other kind of sunfish.
I think it works in the same way that someone raised on a farm has no issues dispatching a chicken. We tried keeping chickens last year, but would never consider them as food, and putting one down was a nearly traumatizing experience for me. But that didn't stop me from eating a chicken sandwich at a fast food place the same day.
I don't believe in the short memory span of fish either. It's easy enough to see that our pet fish recognize humans and associate them with food. As previously mentioned, hunger can outweigh good sense, and I would argue that some previously hooked fish don't even remotely understand how the fishing process works.