All of the freshwater aquarium books I have read have advised against temperature shock. That whenever moving a fish to a diffrent body of water to make sure that the new water is the same temperature as the old water. It makes sense.
The books warn of temperature shock, but never explain what it is. They never explain that temperature shock can kill your beloved fish in less than a minute. Temperature shock is serious.
I lost my betta today. I moved it to a fishbowl to break up some serious territory issues between it and three platies. I didn't check to see what the temperature diffrence was between the tank and the bowl. I caught the betta without much of a hastle and put him in the bowl. He started acting strangely almost immedately, darting around the bowl. I thought he was upset about being netted. Then he swam to the bottom and began swimming upside down for about fifteen seconds. At this point I was concerned, I had never seen this behavior before. He swam to the surface as if to take a breath and went belly up and died.
I put the betta back into the tank, fearing temperature shock at this point... He wasn't paralyzed, simply dead. I removed him and placed him in a plastic bag to be burried. It's hard not to blame myself for killing the fish.
I removed the aquarium themometer and checked the bowl temperature. The bowl was 11 degrees F warmer than the tank. A temperature diffrence that seems small to a human was fatal to my fish.
I wrote this partally to help me grieve, but I also wrote it to warn others of the dangers of temperature shock. If you have had an experience with temperature shock, please share it. If this thread can help you save the life of someone's fish, then it is worth the time.