nikon70,I assume you talking about a bala shark, they are known to be quite peaceful,but they do grow up to 1 foot. I would advise not keeping cold water and tropicl fish together. Is your goldfish a "fancy" type,as they can often be bad swimmers and your shark maybe picking on him cause of his trailing finnage. Bala sharks are not known to be fin nippers, you could just have a bad egg!!!