strange Behavior with goldfish

[davidwolf]

One of my Goldfish is picking on the koi, that's little bigger than him. Follows him around the tank all-day, trying to bite the koi butt hole. It doesn't look like it really bothers the koi too much or cares. Do you understand this type of behavior.

[davidwolf]

Heres a pic

[Colin_T]

The goldfish is a boy and the koi is a girl. The male can smell the female and when the weather warms up, he will be trying to get her to breed.