In South Africa, spawning generally occurs in spring to late summer. Most often koi spawn during the months of September and November. If you want to know if your koi are ready to spawn, you can look out for the following signs.
If the female is older than 4 years and your male koi are older than 2 years. Your male koi develop small whitish tubercles or nodules on their pectoral fins and gill plates and when you touch them you can feel their roughness. The males also start to chase the females around the pond and you will notice your koi swimming more erratically around the pond.
If you would like your koi to spawn you should provide them with media that they can spawn on to. Some media that can be used is Spanish moss, artificial grasses, natural plants, vegetable sacking as well as shade cloth torn into strips.
Once they are ready to spawn they will deposit semi-adhesive eggs onto the spawning media. The female can release around100 000 – 500 000 eggs at a spawning. After 40 hours the fry’s body is formed and the eggs if fertilized will take between 5 to 7 days to hatch. The fry will feed off their yolk sacks, which hangs from their belly. Hard-boiled chicken yolk can be placed into a stocking and swirled around the pond to feed your fry. Daphnia and brine shrimp larvae as well as crushed koi pellets can also be used to feed them. After 2 weeks you can feed them powdered food. At 3 weeks some colour can be seen on the fry and they are about 5mm in length.
Koi can also spawn spontaneously without you providing them with media to spawn on to, so if you see bubbles on the surface of the pond, it may be that they have spawned. Koi often spawn in the early hours of the morning, if you notice bubbles on the surface of the pond you must test your water for ammonia. If your ammonia reading is high you must change some water and dechlorinate your tap water. When changing the water you need to be careful not to lose the fry when you are pumping the water out. The parent koi will eat the eggs so, you need to separate the eggs from the parents.