Ten Top Tips For Koi Breeding

Make sure you have both males and females in your pond!  It may seem obvious, but some Koi keepers, either by accident or design, end up with Koi of only one sex in their pond.  Male Koi tend to be slim with larger pectoral fins than the females and they also have rough cheeks.
Ten Top Tips For Koi Breeding

Ten Top Tips For Koi Breeding – This article was first written for and published by Koi Carp Magazine in 2009

1. Make sure you have both males and females in your pond!  It may seem obvious, but some Koi keepers, either by accident or design, end up with Koi of only one sex in their pond.  Male Koi tend to be slim with larger pectoral fins than the females and they also have rough cheeks, and sometimes sides, (it feels like sandpaper to the touch) in the warmer months (water temperature 14-15 degrees Centigrade).  This roughness on the sides of the males is caused by tubercles which they develop in the breeding season when they are sexually mature.  The male vent is concave and the female convex and soft with a pink colour in the more mature fish. The females usually have a more rounded shape and those older than three years may have bellies swollen with eggs.  The fish must be in the peak of health, free from parasites, wounds and infection and the females must be well fed in order to develop good healthy eggs.


A Male Shiro Utsuri with typical slim body shape and large pectoral fins.


A Female Shiro Utsuri with a fuller body shape and smaller pectoral fins.

2. If you want to breed specific varieties of Koi you will need to use parents from the same variety.  For example, to breed Sanke, you use a Sanke female and a Sanke male.  However, you might find that you don’t have the right combination to make a breeding set within your pond and so other crosses that you could consider might be Chagoi with Kohaku, which will produce Chagoi, Ochiba Shigure and Soragoi.  You could cross Kohaku with Sanke quite happily and still get Kohaku, Sanke and Bekko.  If you want to get some recognisable varieties from your spawning, don’t cross metallic koi with non metallic – I wouldn’t recommend breeding with Showa or Shiro Utsuri either as you will get an awful lot of wishy washy pale orange Koi which will never develop into anything vaguely attractive.

3. Normally, a breeding set consists of One female and two males.  By using two males the chance of the eggs being fertilised is greatly increased – also if one of the males happens to be infertile, you will still get some eggs that will hatch.  It is preferable to use a female that is larger than the males she is paired with as the males tend to be quite vigorous during spawning.  The rough tubercles along the sides of the males rub against the female during spawning and, as spawning can take several hours, the female can become quite sore and a little bruised. By using smaller males, this is reduced.

4. It is necessary to provide the right conditions for spawning.  Koi in the wild spawn in shallow water so if you have shallow water in your pond, great, otherwise you will have to create it. Putting selected Koi in a net suspended in your pond is one way of making sure the fish feel like they are in shallow water, another way is to set up a temporary pool, like a show vat or similar, and fill it with approximately 10 -12 inches (25 – 30 cm) of water.  The nets and pool must be immaculately clean and if you are spawning in a pool, use clean water only, do not try to filter the water.

This temporary spawning pool was made using silage liner and the spawning ropes are suspended from the sides and draped through the water.

5. Koi will spawn naturally in late April to July (possibly August) as this is the time of year that the temperature and daylight conditions are at their best.  The fish will spawn in temperatures between 18 – 25 degrees Centigrade and if your spawning pool is a couple of degrees warmer in temperature than your pond, this change in temperature can also be another useful trigger to start spawning.

6. The water needs to be clean and gently aerated to provide a good environment to stimulate the fish to spawn and for the developing eggs and fry.  If you are using a spawning pool, it is preferable not to use water from your pond as this may contain parasites etc that could adversely affect the development of the fry – this is the advantage of using a separate spawning pool.  If you are spawning in your pond however, you won’t be able to do this.

7. Spawning ropes are used to stimulate the fish to spawn.  These are placed in the pond, pool or net on the day the fish are put in and must be squeaky clean and washed without the use of chemicals.  If after washing them you can hang them up to dry naturally in the open air, so much the better.  Commercially manufactured spawning ropes are available for the hobbyist to buy readymade or you could make your own.  Spawning ropes mimic the type of vegetation that the Koi might normally lay their eggs on and so anything soft and with lots of fronds would be suitable.  You could make some from strips of curtain material sown together down the middle and then snipped into strips along each side for example.


Spawning ropes made from net curtain material and frayed to produce a weed like affect.  As you can see, these were used successfully and are covered in eggs!

Our own spawning ropes drying after having been thoroughly cleaned.

8. I find that if you place your chosen Koi in the spawning environment around mid afternoon, they will often begin spawning the following morning.  Leave the fish alone once everything is in place.  If you interrupt the fish during the first stages of courtship, you might put them off and if you interrupt them after ovulation has taken place, the eggs may not be laid and the result will be septicaemia and ultimately death of the fish.

9.  If your fish are spawning in the pool or in the net, keep a distant check on them and once in full swing, little will stop them but still keep a low profile and try not to disturb them. Once the female has stopped laying eggs, carefully remove the parents to stop them eating the eggs.  If the fish don’t spawn on the first morning, leave them in for two more nights only.  After this time, return them to their pond.  DO NOT FEED the fish in the spawning environment as this will pollute the water and reduce the chance of any eggs hatching. NEVER try to hand strip the eggs from the female.  Leave this to the professional fish breeders.  Inside the female, the eggs are held in place by a bag which must be dissolved prior to spawning.  This only happens moments before the eggs are ready and if you do try to hand strip the fish before the eggs are ready, you will severely damage the fish, possibly causing death.

10. Once you have removed the parent fish slowly trickle in some fresh water to your spawning pond and carry on providing gentle aeration.  After you have added some fresh water, dose the pond with Malachite Green which will stop fungus growing on the eggs.  (For dosage rates just follow the manufacturer’s instructions.) Within a day or two you should be able to see the fry developing inside the eggs.  Not all the eggs will survive and those that look solid and white are probably dead. Those that are transparent and which develop two black dots (the developing fish’s eyes) are likely to hatch within a few days.  When the tiny fry first hatch, they are still surviving on the remnants of their yolk sack – they can’t eat because their mouth is still developing, their swim bladder is not yet operational and they have a sticky pad on their head which allows them to stick to either the side of the pond or the spawning ropes for safety.  After two or three more days the baby Koi have almost finished their development and are fully functioning little fish.  They swim up to the surface and take a gulp of air which they transfer into their swim bladder, giving them buoyancy. The exact timescale over which all this takes place varies and depends upon the temperature of the water.  The warmer the water the faster the development; cooler water slows the whole process down.  Either way, it usually takes 7-8 days after spawning before the tiny fry have “swum up” and taken that first gulp of air.  After this you can remove the spawning ropes.  Try and keep the water as fresh as possible with lots of slow water changing.

A close up of Koi eggs in the first stages of development.
Tiny Koi eggs on a spawning rope – some are white and will not develop and some are clear and have a good chance of survivial.
Freshly hatched Koi fry are almost transparent, apart from their eyes!  Over the next month their colours and scales will develop.
The speed of the egg development is incredible!

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