No to sound short...but Ottos don't go with goldfish. Ottos are tropical and should be kept at 80*, gold fish are coldwater fish. He is probably sick from being in the wrong conditions. I would take him out of that tank and put him in your sick tank. He need to be alone, but if he has swollen belly ther could be an internal infection happening. Treat him with Maracyn Two , I think ottos will be ok with that med.
The goldfish will eat him if he dies in that tank. It's never a good thing for any fish to eat sick fish. They could catch what may be wrong.
Sorry about your otto, but you should have researched before buying.
