Goldfish biting each others fins?!!?

[Dado]

My goldfish started chasing each other and biting each others fins. From 6 goldfish, only 2 survived. Why is this happening since I've had these goldfish for more than a year, and it never happened before. :confused:

[avoxo]

Hi Dado, sometimes goldfish will become territorial, try moving some of the decorations around in the tank, if you don't have any try to put a couple in to mix things up for them. Another reason is they could be breeding and the males might be chasing the females around to the point of death. Hope it helps.

[stik6shift98]

what size tank is it????