about fish breathing

Question
Why does a fish open and close its mouth many times in a minute in an aquarium?

Answer
Akshita, This is almost always caused because of lack of oxygen in the water. Simply remedied with an air stone and an air pump. The bubbles will create agitation on the surface of the water will envelope the oxygen into the water and that will stop their gasping. This is very common with goldfish or larger fish and not enough filtration. Good Luck, Tina