When I came home from work today, I was shocked to see my one-eyed yellow eye anthias Pseudanthias lunulatus, Lucky, with his mouth stuck open! Unfortunately, I've heard of and seen this happen to anthias before when they are stressed out, and they usually don't come back from it. I have no idea why this happens, but I've always wondered. I think Lucky may have just been surprised by the door opening abruptly (the tank is right by the front door). Lucky is blind in one eye and often swims full speed into rocks and other objects in the tank, so it's possible he injured his mouth doing that. Luckily, Lucky was able to close his mouth after a few minutes and is eating right now.
It kind of looks like this, when an anthias' mouth is stuck open.
Here's a picture of Lucky right after I brought him home. He was still a little thin in this photo, but he's doing great now.
I've also heard of and seen stressed anthias who bend in the middle and can't straighten themselves. They usually die shortly after. Small anthias are delicate little creatures and should always be handled with great care! Don't expose them to sudden bright lighting, changes in water parameters, aggressive fish, or other stressors. Stress kills anthias.