One goldfish chases another

Prat wrote:

Thanks.
I too was hoping it was just mating. But yesterday the fish that was
chased died. I suspect it was due to the stress of the bully bothering
him.

The bully is a small ( just a tad above 1 inch) comet and the victim
was a common shubunkin ( the one with a single tail ). It was slightly
smaller than the bully.
Does mating occurs across sub breeds of goldfish like the comet and
shubunkin or comets always chase others.

Thanks,
Prat

Yes, they are all the same breed, just different variations.
Like dogs really - they will all breed!