Koi Spawning Brushes Made from a soft material that will not harm fish, these brushes are commonly used in koi ponds to encourage fish to spawn. Simply place the brushes just below the water level, one on top of the other, at the edge of your pond. As the fish spawn on the brushes, the eggs will attach to the soft bristles, allowing the eggs to be separated from the brood fish so they will not be eaten. The brushes can then be placed in clean filtered water and eggs will hatch in 3–6 days. Brushes measure 48" long x 5" diameter and are sold 2 per pack.