Lump-like Bulge on Goldfish

So I got 4 fish about 6 months ago, never had any problems or issues until last month. I noticed my one gold fish on both sides of his dorsal fin he has these lump like bulges. They started small but as time went on the are now pretty big. Tonight I changed the water of the tank and just was watching it and now see there's like small spots of blood under his skin, like the bulge is about to explode.... so my questions..

1.What is it?

2. If he does die or the bulge explodes, will it kill my other fish?

I do have pictures of it but I am new to this site, so I'm not sure if or how I can upload them, so if you think you may know what it is and are interested into seeing the pics please email me!

Thanks so much!
[email protected]