Jack, I missed your reply. Here are a couple of other articles. One by Dr. Shimek and one by Richard Harker.
http://www.animalnetwork.com/fish2/a.../1/default.asp
http://www.animalnetwork.com/fish2/a.../1/default.asp
Both articles are temperature based. It does not appear that they agree with one another though.
FWIW, Ron is a great guy but I think the phrase;
doesn't suffer fools, was written with him in mind.