Why do your fish swim at the top of the aquarium?

They may be hungry. Usually fish will "break water" to feed. Go to a pet shop and get a little book on guppies and that will help you raise them. Good luck Marcy I would also recommend having the water tested by an aquarium store. High Ammonia and or Nitrite levels will cause them to go to the surface and appear to be "gasping for air". Acceptable parameters are less than 2ppm of Ammonia and less than 25 mg/L of Nitrite. Also watch other tank inhabitants closely since guppies by nature are very timid fish and do not tolerate aggression very well. If other fish are harassing them, their only refuge is often the surface of the aquarium.