Mike Robinson of Keystone hatchery in Illinois once told me he considers bluegills a "Goldilocks" species. That is he doesn't like to handle them in too cold of water or too warm of water. I've been told the larger they are the more sensitive they are too.

My guess is to cold of water sets them up for fungal issues and too warm of water may set them up for bacterial issues.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.