A: That is an indication that the oxygen level in the water is low. They are not gulping air, they are gulping oxygen rich water from the surface. If this happens constantly, you must do something to enhance aeration. Just get the water moving! it is the friction of the water and air that transfers oxygen to it. If this happens just after feeding, they are looking to maximize their oxygen intake in order to digest the food. Just feed a little less next time. Frequent feeding is much better than one big mouthful.