Hi and welcome to the forum
This is a new one for me and that is saying something.
Blurk. sorry but that's gross
It's not a normal fish disease and I would guess it is either a bacterial infection or some sort of parasite that has infected the fish in the wild. The fish has then been brought into captivity and the parasite is living happily on and in the fish.
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Can you post some more pictures of the fish and the entire aquarium?
What is a good bacterial ball?
What species of catfish is it?
How long have you had it for?
Any idea if it's wild caught?
How often do you do water changes and how much do you change?
Do you gravel clean the substrate when you do water changes?
What sort of filter is in/ on the tank?
How often and how do you clean the filter?
What other fish are in the tank?
What are you feeding the fish?
How often do you feed the fish?
Is there driftwood, algae and live plants in the tank?
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I would do a 75% water change and gravel clean the substrate every day for a week. See if it helps. If not then antibacterial medication. But try to get a broad spectrum liquid based medication first (something like Waterlife Myxazin or Triple Sulpha), rather than antibiotics. If you have to use antibiotics, try to use them in a bare tank so the medication can work on the fish rather than being wasted on everything else in the tank.