Gills
Hi.
How old is the tank?
How are your water parmeters?
Have you tested the water or had it tested at your LFS recently?
Fish gasping at the top usually means that they are having trouble breathing.
Ammonia poisoning can cause ragged gills and heavy breathing.
Are the gills brown? That means nitrite poisoning.
Nitrate poisoning although less toxic than the previous two is still able to kill fish.
I would do a large water change. 50% at least. If you have a test kit at home. Test the water and tell us what the water is like. Befroe and after the water change.
If you can add aeration (Airstone) to the tank that will help after the water change. If you don't have a test kit go asap and get it tested, but right now the water change is the important part.
Good luck