My fish seems like he cannot breathe but I cannot figure out what it could be?

At first I thought that he had flukes but I did a water treatment thing but he still acts weird, the flukes are gone. He likes to stick his head out of the water like he is trying to breathe, and he swims forward and backwards in the fish tank near the surface. Does anyone know what this could be?My fish seems like he cannot breathe but I cannot figure out what it could be?
What type of fish do you have? The reason I ask is Labyrinth fish do that. For example, Gouramis are Labyrinth fish and they literally have a lung that allows them to stick their heads up and breath air.





Otherwise, the next question is do you have an aerator? Make sure that your tank has plenty of Oxygen as that could be the culprit to your fishes behavior.My fish seems like he cannot breathe but I cannot figure out what it could be?
More info please. What kind of fish? How old? What is the tank setup? Any other fish or critters in the tank? These may all be factors.
I think you should change the water in the tank. there might not be enough oxygen in it.
try doing a 25% water change with dechlorinated water.





but it could also be low oxygen levels





if its a gourmai then it normal because they have a laborynth organ that allows them to stick there head out of water and breath.