Mating game by goldfish

I HAVE a pond on the patio with half a dozen goldfish in it.

Most of the time they’re quite boring, skulking around under bits of vegetation and only becoming active when I sprinkle flakes of goldfish food on the surface. But over the past few evenings this has changed.

At a certain stage in the evening they start chasing each other round the pond at ferocious speed and, if the chasing is successful, butting the other fish in the flank. It’s easy to ascribe this sort of behaviour to ‘play’ but I suspected it was more significant.