Is it true that you should let catfish swim in clean water for a few days after catching them before you kill and clean them?

I've never done that, always just nail it to a tree.

I dont.

In my opinion most freshwater fish have a muddy taste. As far as your question I don't know having never

done it with fish. I have put some animals in a pen and fed them a diet of corn to clean them out. Generally a possum

or coon. Maybe a small feral hog.

I never have, catch and release into the grease.

If you can. That would get the muddy taste out of the flesh. {Catfish raise for commercial sale are raised in clean water.}