Why does my common gold fish's skin comes out?

Question

I bought a couple of fishes 2 weeks ago. I bought: 1 parrot fish

1 common shark, 1 big shark, 2 common gold fish and 1 municipality fish (one who cleans the whole tank). In that the common gold's skin comes out a little by little. Please help me and tell what to do next

Answer 1

maby it is stressed because it is kept in a tank with completely incompatible fish  

Answer 2

Its not coming out its getting eaten. Common Goldfish are not compatible with any of the fish in your tank.

Answer 3

Sounds like it might have bloat. It is caused by constipation. Standard procedure is to try feeding 1/2 a shelled, boiled pea to loosen things up.

EDIT: Wait... but "coming out" do you mean "expanding" or "disappearing"? If it is just gone in patches, that is because your parrot cichlid is picking at it. The shark may be nipping a bit as well. Also- you have a tropical tank, but goldies are coldwater fish...