Professional Koi Breeding

Although koi are bred very successfully in Israel, the Far East, South Africa,throughout Europe and in the United States, Japan is still considered the home of Nishikigoi. There are several regions in Japan that are synonymous with high-grade koi. These are Hiroshima, Shizuoka, Saitama, Toyama and Kyushu. However the prefecture (the district administered or governed by a prefect) of Niigata is by far the leader. The breeders here being the most revered in the world of Nishikigoi. These days even breeders who are following on in a long established family business, have probably attended university to study fish farming and may have travelled the world in order to learn from the best breeders the techniques used, and to study the complexities of fish genetics.

The 'mud ponds' of Japan are famous and synonymous with koi breeding. They are used for growing on the young fry and Tategoi. They are hand made and are sited on hillsides that used to be occupied by paddy fields. These days however, there is more money to be made from cultivating Nishikigoi than there is from rice production. Excavators are used to dig out new ponds and the clay is tamped down by machine to make them watertight. The clay is also smoothed off for the benefit of the koi and to make it easier for netting them later in the season. The ponds vary in size from about 60sq metres ( 646sq feet) to vast ones of many hectares. The depth will depend on what they are used for, up to 1m (39 inches) for fry, to over 3m (10ft) for the larger fish.

At the start of the new season, in early spring, the ponds are drained and allowed to dry out. They are then rotavated and pure lime is added to the mud. This not only kills off any parasites that may be present, but also helps to increase the pH value of the water. The water used to fill the ponds is natural spring water from the mountains which is very acidic. Phosphates and minerals are then added to the base before it is tamped down again ready for refilling.

Pools are prepared for the actual spawning during May. Rectangular spawning nets about 1m (39") deep are lowered into the pools and suspended there. These nets prevents the spawning koi form damaging themselves on the hard sides of the permanent pool and are also used as the first home for the eggs and subsequently the fry. Kin-ran (soft, artificial spawning grass) is attached to the base of the net to encourage spawning. Brood koi are added to the pool in June, usually one female to three males, to encourage natural spawning. Experience has shown that immature fish are not suitable for breeding as young females do not produce many eggs and young males do not produce enough milt (sperm) to fertilise a large number of eggs so using them commercially would not be cost-efficient. Therefore, mature females, ie. over five years old, and mature males, ie. over four years old, are normally used.

On hatching the fry are nothing more than a transparent sliver with eyes and a yolk sac, they are upright in the water. They feed off the yolk sac initially and their swim bladder gradually inflates so that within a day they are horizontal in the water and free swimming. At this satge the fry are about 7mm (0.28") long and are a pale yellow in colour. As the yolk sac is depleted they start to dart about looking for food. It is at this stage that they are carefully taken to the prepared mud ponds to feed on the infusoria, and grow on during the warm summer months. A few weeks after this the first cull ( something picked out from others, especially something rejected because of inferior quality) takes place.

Countries outside of Japan often use hormone injections of gonadotropin (removed from the pituitary gland of wild carp) to bring on an almost instant spawning. This method is used widely throughout the worls for the mass production of fish for the table ie. salmon and trout. Nishikigoi breeders however, are not in agreement with this method of breeding koi as it is seen as a risk to their valuable broodstock. Also, their methods pruduce more than enough fry for then to econimically handle.