Ranch fish getting bullied

[Dermot40]

I would like some advice on 1 of my Ranchu fish getting bullied by some of the tank mates. I have 2 Ranchu fish and 3 Oranda fish. 1 of the Ranchu fish has all of a sudden started to get bullied by the Oranda’s yet they have all been peaceful tank mates for 9 months.
I have had to remove the Ranchu into a tank of its own to give it peace. The Ranchu is perfectly healthy my water readings are perfect.? Is it possible that the Ranchu is female and the Oranda fish are all male, and she is “ in season “. Or can the Ranchu have eggs and attracting the males. All 3 fish can be very rough on the Ranchu knocking it into the sand and chase it constantly nudging it from behind. Since I have removed the Ranchu from the main tank everything is back to being calm.
Can someone give me some advice please.

 

[Colin_T]

Video of the fish?
Upload videos to YouTube, then copy & paste the link here.
If you use a mobile phone to film the fish, hold it horizontally (landscape mode) so the footage fills the entire screen and doesn't have black bars on either end.

If the fish are chasing the ranchu around and nudging its butt, they are probably trying to breed with it. Males are slimmer than females but it's hard to tell with fantail goldfish due to their body shape. Males will get small white dots on their gill covers and pectoral (side) fins when they are in breeding condition. Females don't get these dots.

Goldfish come into breeding condition after being kept in cool water for a few months and then having the temperature rise.