i have a big holding tank for my feeder gold fish, i feed them for my peacock bass (cichlas), what i do i once in a while i get two one with a big tummy and one slim, which with luck should be female and male.
place them in a separate tank or shallow tub with air tube, they should lay eggs with in 4 days if not get another pair. i sure 4" feeders for this.
if they laid eggs you should see small round white eggs on the bare bottom glass or tub.
Thanks