As a little aside, last week I changed my aquarium water, and added water that was a little too warm. Maybe only about 5 degrees F too warm. It stratified on the top 8 inches or so, and the filter didn't stir it up very quickly.
I fed the fish, and all but a couple of them REFUSED to go through that warm layer to the food. I suppose this relates to when we observe our pond fish not coming to feed at the surface. They may not feel comfortable jumping through the sharp jumps in temperature, and will instead wait for the food to come down to them.
