If the fish is sick then my guess would be mouth fungus or maybe columnaris... I recently went through a columnaris disaster and it more commonly impacted the mouth region of fish and turned it white. If other parts of the fish are turning white / getting discolored then I would guess columnaris based on the research I have done. I believe a true fungal infection (mouth fungus) impacts only that region (not positive though). Columnaris is bacterial and can impact any exposed area on the fish.

Either way I would remove them and hospitalize in a separate setup. If it's columnaris you could be in big trouble real fast. I lost 50% + of my stock within a few days of noticing it. From what I experienced within the past few weeks once a fish has the white discolorations on their mouth and/or body (externally visible infection) they are basically 100% going to die.

I can say with confidence that it is probably NOT columnaris if the fish is active and acting normally. My infected fish acted strange and were very dormant/lazy when they were sick. Was very easy to tell there was something wrong with them.

Could be wrong though... I am no expert on disease just sharing what I have experienced...

 

Hi JungleTrek,

I had a Corydoras aeneus (Bronze Cory) with a similar problem; it seemed to develop a white fungus infection under the 'armor' (bony exoskeleton) so the poor fish looked almost white. I didn't think it would last out the week but I treated it (and the whole tank) with Melafix per the directions. It took almost 10 days but the infection went away and that fish still swims in my tank. It did not harm my plants whatsoever.

 

Thank you guys for the response !
I'm keeping an eye out if any visible stuff is appearing on my fish. I hope its not Columnaris !
For now all of my fishes are behaving normally, and are active. (including the ill one)

I'm trying to get a small quarantine tank ASAP, and I'm getting some fungicide medicine.
I have to look up what medicines are available here in EU, Im sure there are quite a few to choose from.
It's about time to get a decent quarantine tank, I was neglecting this for too long.
(fortunately I have plenty of stuff ready, filter, air pump, etc.)

Thanks again guys, I'll get back to you when this is solved

 

Yeah if they are acting normally it is likely not columnaris. My fish were really struggling by the time they showed symptoms

Good luck!