Rainbow Unable To Open Mouth, Internal Parasite?

[illusion54]

I have a juvenile neon dwarf rainbow and as the topic title says, it cant open its mouth. As a result, the little guy can not eat. Its so sad cause it tries to peck at food but cant open its mouth. My guess is internal parasite of some sort? Should i treat it as a parasite?

 

[WILDER]

Never heard of it before, can you issolate him, as something is not right, he hasnt got anything lodged in his mouth so he can't open it, why do you think it's parasites.

 

[black angel]

I know that when a large fish cant open its mouth its usually due to some sort of trauma and can be down to other fish being aggressive or from fighting and sustaining a dislocated jaw.
Sometimes if they eat something like a small stone it gets stuck in the mouth and you would need to take the fish out and gently press underneath the mouth to see if it will open but dont force it.
Another thing to look at as well is that dietary defficiencies can cause this to happen but i dont know how you can get him to eat again.
Have a look under the gill flap as well to make sure the gills are bright red.