Cardinal Tetra Has Become Deformed

[Emilyb665]

Hi
Can someone please help me. I have one cardinal tetra in the shoal that has suddenly become deformed. It has a weird shaped body and has developed what looks like a lump under its mouth. It's tail is also looking very thin

 

[Byron]

If you can post a clear photo (or video), it will help us.
 
Byron.