my new figure 8 puffer fish has a strange growth?

[Josh]

Is it a bulge or like a cottony growth? If it is like cotton it is probably columnaris or cotton. Hope I helped!

[BigRudy]

i bought a figure 8 puffer fish a few days ago, and after about 2 days of being in my tank, he developed a large lump on the side of his belly, its whitish grey, it literally is about half the size of his belly. it looks like it is getting bigger almost every day. the only thing i saw online was that it could be his food, but i doubt it, its to far to the side. does anyone know what this could be?