Growth on inside of Jack Dempsey's mouth. Anyone know what it could be?

[theskibag]

Hi guys,

My Jack Dempsey has developed a growth on the inside of his mouth in the last few weeks and doesn't seem to be going away. Would anyone know what it is?

Tank Mates include arowana, clown knife, pangasius, peacock bass.

Sorry for the bad camera phone pics

Thanks,

Alan.