I have a pond with Koi and goldfish who lived happily together for a few years.
Today however all the fish apart from the large Koi ganged up on another goldfish and seemed to be trying to push it out of the water. They were quite ferocious in their attempts.
My wife netted the fish and put into a seperate pool after which all seemed to cool down.
The fish appears to be unharmed and has no visible signs of disease, so what do I do now?