Aggresive(well actuallly nibbling)goldfish

Question

I have 5 goldfish in the same tank. Three common goldfish, a fantail and a black moore. One of my common goldfish(about 1")will nibble on my back moore(about an inch and a half), my fantail( about 2" including tail)and my other common goldfish bully(about 3").My fantail and back moore are completly helpless and inosent.And for some reason my other common goldfish(about an inch and 1 4th)doesn't do anything. He just sorta patrols the fish tank.Do my 2 bullies need to be separated?

Answer 1

sqeeze her  

Answer 2

nibbling is a sign of stress.

either your tank is too small, 20+ for fancy goldfish and a pond for common goldfish.

or your fishes are new to the tank and curious about each fish. this behavior should stop after a few days.