New puffers! But one needs your help...

So I just FINALLY got my f8 puffers! It was slim pickins, but I found 2 that with some TLC look like they'll be good. They were in with neon puffers that ate their tails, and 1 big gsp that was eating all the food.
Anyway, the cuter of the two. has a weird bump on his tail. IT's almost bluish and looks to be raised. Other than that and being a little thin and tailless, he looks happy and healthy. Could this be an injury or does it sound like a fungus?

if anybody has any tips on *how* to take a picture of a fish, I'll be your friend forever, lol. I really want to get a pic so I can see if he's ok, but I just dont know how. I get pictures of blurrs and flashes. I hate my camera a lot.

eta:
the closest thing I can describe it to is it sort of looks like if you pinch yourself and break a blood vessel under the skin....It's raised and blueish like that. Not a perfect circle or anything, it's got squiggly edges and one part looks only partly connected to the rest of it. does that make any sense? it's about the size of his eye, and he's about an inch and a half to two inches long.