Anybody seen anything like this before? I've done some cursory searches online and haven't found anything concrete. I suspect its some kind of cancerous tumor which should be relatively harmless to the fish. I'm not really worried about it, just curious if anyone has some additional insights (or should I be worried?).
Backstory: I've had a school of these Denison's for about 1.5yrs (90g community with lots of other fish of all kinds), and shortly after getting them, this guy developed what originally looked like a popped scale on his black stripe. I thought nothing of it until about 6 months ago when it grew a bit and got "wobbly". A couple months ago, it grew (within a matter of days) into what it is now, and the trailing "bubble" now looks like it might fall off. Just the other day I noticed another small tumor/bubble develop on the other side right behind the eye. He's been fine all along - eats, poops and swims normally... No bleeding or sores other than this strange mass.
Water quality is excellent and stable and always has been (pH 7ish, medium hard). Diet is a mix of flake, pellets, live white worms, frozen bloodworms, frozen brineshrimp, zucchini, peas and watermelon.
Sorry for poor quality pic. These guys never stop moving so hard to get a pic that isn't just a blur of colour!
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It looks like melanoma (black pigment). Time will tell... if it is that he's not going to live long.