Preparing for professional koi spawning

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. Spawning usually takes place within two days of the fish being introduced to the pool. The improved breeding environment of the net and spawning grass encourages the female to drop her eggs and these are immediately fertilised by the male. Optimum water temperature is 17 deg. C (62 deg. F). Usually starting early in the morning, spawning can take between five and nine hours to complete. A mature female can release up to 400,000 eggs in one spawning. Spawning is usually overseen by a member of the breeding team in order to ensure that the female does not become stressed during the mating process, and also, to remove the parents after spawning has taken place so that the parents do not eat their own offspring. The adults are checked over and removed to a mud pond to to rest and recuperate. A mild malachite green solution is added to the tank containing the newly hatched eggs in order to prevent Saprolgenia (fungus) attacking them. Constant checks are made on the water quality in the pool to assess ammonia, nitrite and oxygen levels and when necessary spring water is slowly and constantly added to create a gentle water change. The aeration is heavy at all times to maintain high dissolved oxygen levels. The eggs will hatch in 3-5 days dependant on water temperatures.