aggresive gold fish

I have a 10 gal tank and 4 fan tails and one regular gold fish in it and the
regular gold fish kept biting on my whitish gold fan tail and on its behind
and all over and then another fan tail joined in to bit on the same fish but
not any of the others. i took the two aggresive fish out and put in a large
fish bowl. the other fish in the bigger tank are not biting the white one but
why were the other two biting it? The would actually hold it down on the
bottom of the tank and aggresivly bite it all over or they would constantly
chase it around and bite it but mainly the reular gold fish was the most
aggresive. Please help i need to know if something is wrong with them.