Filefish's mouth won't close

[bat21]

I noticed my filefish will not close its mouth tonight and is also breathing very rapidly. Behavior seems to be fine though and he actually ate a ton. The rapid breathing has me worried though. What could a continuously open mouth mean?

Video: https://youtu.be/2ReLWE41FLo

 

[Dkuhlmann]

My male Mocha clown did this about a week ago and as fast as it started it stopped. Some kind of lock jaw I suppose. I don't know of a cure for it, but I've heard it happening from certain foods if fed continuously and mostly around Krill. I don't feed krill so I'm still stumped about yours and also my clown.

Hopefully someone can explain what its from, I never got an answer to exactly what caused it or how to cure it.