Almost looks like a parasite for a sec but it could be some overgrowth from an injury. Like a growth similar to what people get from keloids after a cut.
Just an analogy. Watch for now and see what the other memebers say.
It looks like a parasite to me. If I saw it on any of my fish I would try a multi ingredient parasite med first. I like the Tetra Parasite Guard. It has a few different meds in it, but you need to run the full course of treatment which should be three applications.
If it's anything it's parasites so I'd treat with some parasitical medicine, but I sometimes see things like this in Polys and it often times just looks like part of the bichir.