Uaru fish in problem

[Aalok bairwa]

I was not at home for last 5-6 days my family was doing regular changes and tank was half filled for 3 hours and when I came yesterday I saw swelling near mouth of uaru and today it is like this

Is this natural or some fish attacked as i don't have any fish that can do this only have severums and angel and other peaceful fishes

It is like uaru is growing teeths but it have low energy but it's active and responsive i removed it from main tank and settled in quarantine with old tank water

 

[Deadeye]

Looks like an infection is eating away at the flesh - it could have stemmed from an injury. I’d get it into a qt with an antibiotic ASAP - something like kanaplex or neoplex.