A Brief Guide to Koi Breeding

Koi (or nishikigoi in Japanese) are some of the most common pond fish species in the world. Although commonly mistaken for larger goldfish, koi are actually members of the Cyprinid family and are descendants of various species of wild carp.

We often see koi fish in ponds or water gardens where they’re kept for decorative purposes. Every year, thousands of hours are spent on breeding koi. The koi breeding process can be divided into three parts: spawning, culling and harvesting.


A mature male and female koi are chosen from a group and placed in a single pond. Female koi have a rounder appearance than male koi, especially when they’re about to lay their eggs. Males are slimmer and develop a slight roughness on their gill plates before mating. Once the male and female koi are in the pond, you should check that the fish have something suitable to spawn on, The BlackKnight spawning brushes are ideal for this.

Plants are essential for a fully natural koi breeding process. If ponds have no plant life, breeders should use koi spawning brushes as an alternative. Spawning brushes emulate water plant life and attract females to lay their eggs on the soft bristles.

When a female koi is ready to spawn, she searches for plant life and rests there, as though to create a nest. The male koi then swims towards the female and bumps into her until she releases her eggs. Once the eggs have dropped, the male will spray them with his sperm. At this stage it is possible to remove the spawning brush to another oxygenated, filtered tank or pond to maximise the number of fry and prevent them from being eaten by the other fish before they have matured.


Farmers cull their koi crops several times throughout the year. Once the fingerling koi reach a length of 1 to 2 inches in length, farmers transfer them into fish hatcheries. The culling process involves selecting the koi that show signs of potential then placing those fingerlings back into the pond.

As the fish grow, they are culled repeatedly throughout the year. Some fish are removed from the group while others are sold. The best are taken care of in the pond for even further growth.


The final step is harvesting the koi. Farmers use long, flat nets and sinking pellets to lure the fish into the corner of the pond. After the fish have huddled together on the net, the farmers pull the hems and transfer the fully grown koi to tanks.

At Black Knight, we have products that are excellent partners in koi breeding:

A great alternative to spawning mats and mops, the Black Knight spawning brushes aid koi in their reproduction cycle by providing females a suitable place to lay their eggs.

Our vortex brushes are designed for the effective removal of suspended solids from vortex chambers in ponds and fish hatcheries.

For advanced filtration systems in ponds, hatcheries and fish farms, filter brushes are the ideal filtration solution.

The Wizard Fibre is fine glass fibre for mortar and concrete reinforcement in concrete ponds.

For more information about our products, call us today.