[Zbrafish] Mouth deformation

[AKC]

Hello!

In the last couple of days I observed that a fish in one of my tanks
have developed a strange mouth deformation.  The first thing I noticed
was that the fish has its mouth open all the time.  When I observed
closely it seemed like the lower jaw bones got dislodged.

I couldn't take good pictures, so I took this short video:
http://sites.google.com/site/hydzebrafish/Home/L1000299.MOV

The fish with the deformity is nearer to the camera when the movie
begins.  I tried to maintain focus on the same fish.

Does anyone know what the problem with this fish is?

Thanks in advance.
Anil