lump on fantail

Has anyone else had a fish that had a large lump on their back almost
on their dorsal fin?

My fantail is about 6" and this lump just appeared. I don't know what
it is. A tumor?? He's about 6 1/2 yrs old. He's healthy. I've also
noticed lately that his scales are "pearlizing". Some of them are
really white and shiny. No white spots like Ick (had that before), but
like a white pearl color. I don't know if that's related to the lump.
I don't know I can do to see if the lump goes away. Any ideas?

Thanks!
Angi

Don't laugh at me...please! But, is it just the fish's makeup or is
there something going on with my tank (food, water, etc.) that could
cause it? In other words, could he not have enough of something in his
diet or something like that. I have 2 others and if it's something I
could control, then I'd like to.

Thanks!