Blister like lump on black widow tetras mouth

[Jrcall]

I've just come home from work and have noticed that one of my black widow tetras has got a blister like lump on its mouth. I can't really find anything online to help. I changed their water a couple of days ago so levels are normal. I haven't noticed it before so either it's been there a while and I just haven't noticed or its come on quickly. Any suggestions or help for this woukd be appreciated

 

[Animallover😍]

It might be fungus. But to me it looks like the fish got food stuck in its mouth! Maybe try to get it out? I dunno

 

[PewPewChris]

Lip injections?