Handle your goldfish as little as possible to minimise unnecessary stress. Always use a net to catch your fish. Gently corner them and then catch them quickly.
Common illnesses for goldfish are fungal infections of the skin, parasites and constipation. Infection caused by lost scales, split fins and wounds can be treated with one of many treatments available. Your local Jollyes will be happy to advise you on the many fish remedies available should your goldfish become unwell.