He's cold, and it's no fun being a cold fish! When the temperature drops below what is normal for your fish, he will shimmy, or swim in wavy movements, but not really go anywhere. He may also huddle around a tank warmer if one is available.

To warm up a cold fish, turn up the warmer and gradually warm the water at a rate of one to two degrees Fahrenheit per hour.

Fish that are too warm, on the other hand, may try to jump out of the offending water and/or breathe heavily. To correct the problem, slowly lower the water temperature by replacing some of the aquarium water with pretreated cooler water. Monitor the temperature during cooling with an aquarium thermometer. Also, make sure that your aquarium is not in direct sunlight.