dark spot on niger triggers tale

[jameslafo]

I was just wondering if anyone knew what this is. My friend told me he woke up to see that on his triggers tale and I need help identifying what it is... I think it’s some sort of fungus or sometning but let me know what you think it is

 

[vetteguy53081]

Appears to be bacterial
First thing I’d do is to confirm:

ammonia
Nitrate
Ph
Salinity
Temperature

Then a water change as this is often associated with water quality

 

[lion king]

Appears to be fungal to me, if I'm not mistaken that looks like cyano and extreme algae in the background. 1st order of business would be water quality, honestly that tank does not look clean at all. @Jay Hemdal can give you the best advice on treatment.

 

[Jay Hemdal Verified Community Expert]

The ring around the center area is interesting - bacteria and fungus grows in circular lesions like that, but I think they would be more uniform in their growth pattern. Parasitic copepods would account for the brown centers, with tissue damage around the edges. If it were my fish, I'd give it a 150 ppm formalin dip for 45 minutes under good aeration. That would kill any copepods and would also get a start on treating it if it is a fungal infection. Trouble is formalin isn't readily available. The next best option would be a 5 minute freshwater dip. That would dislodge parasites, but wouldn't help if it is fungal.

Jay