male blue gourami not happy

[kingzac]

My male blue gourami has taken to hiding in the top corner of my tank behind the filter for the past three days. He seems to be gagging for air but there is plenty in the tank as I have a powerhead and an airstone. There is no sign of any disease but his colour has gone a lot darker than normal.

Any ideas?

 

[Colisa lalia]

Sounds like stress, are other fish bothering him?
If not he may have an internal parasite, probably gill flukes treat him for that, and he should stop gagging for air.