Selecting pairs of fish
There is some discussion of how to tell the sex of goldfish elsewhere on this site. A brief recap:
- Males are the only ones that can be reliably identified
and then only in breeding condition. At this time, they
(sometimes) develop breeding tubercles on their gill
covers and the front rays of their pectoral fins. These
look like a sprinkling of fine salt or sand on the fish.
Some people mistake this for Ich the first time they see
it. One difference is that the breeding tubercles do not
spread all over the body and fins.
- Females are most often identified when your males (quite
possibly in breeding condition, but not necessarily with
tubercles visible) start chasing them and nudging their
sides and vents.
Be aware that males will relentless drive females to
exhaustion, so you need to make provisions to remove the female
when spawning is done or to provide some shelter in the spawning
tank. Also keep in mind that goldfish voraciously eat their own
eggs, so you want to remove the spawning material (or the fish)
once the action has slowed down.