How do you breed koi?

 Koi carp are egg scatterers with slimmer, smaller males chasing the larger females before pushing them into weeds and expelling thousands of eggs and sperm together. Do nothing in a large planted pond and your koi may spawn of their own accord when the water warms in spring and summer. They eat their own eggs after spawning so wait to see if a few survive or remove the plants they spawned on and raise separately. 

If you want to deliberately breed koi, separate a ripe female and two males and move them to a spawning vat containing only water, an airstone, and koi spawning brushes. On a sunny morning if the temperature is right they will spawn before the parents are placed back in the main pond and the eggs and fry are raised separately. 

Professional breeders may even hand strip selected males and females, squeezing the fish’s flanks by hand and mixing eggs and sperm in a bowl. Fry can be placed in a growing pond consisting of green water and live Daphnia or raised on newly hatched Artemia. Young koi on sale have all been through the culling process whereby only the fastest growing fry with the best patterns are selected. A high-quality fish may literally be one in a million.