oscar with bump on tail, pls help

Hi! I've had my Oscar for about 2 years now, ever since he was a baby. He's always been in perfect health, but I've noticed a kink at the base of his tail. Now where the bump is there seems to be a little open sore, maybe an ulcer? My ropefish once had an ulcer and we just took him out of the water and dabbed some mecurochrome on it and it went away. By looking at the photo of his tail, can anyone tell me what could've caused the bump as well as the sore? I'm scared it might be something serious. I love my Oski! There are no other fish in the tank that could've hurt him.

I hope to hear from someone soon!!!:(

Monica

I'm not sure, but I think you should post this is pet health.