Breeding Koi

On the face of it, breeding Koi seems like a simple exercise – you put a male Koi and a female Koi together, they spawn and you then get hundreds of thousands of eggs which hatch out into hundreds of thousands of Koi and this time next year, you’re a millionaire! Clearly, if it were that easy, more people would be doing it. So what do you have to take into consideration when breeding Koi?

If you want to breed specific varieties of Koi you need to select specific varieties of parents, if you don’t do that you will end up with a whole lot of generally unattractive Koi of indeterminate variety. Female Koi can produce between 100,000 – 120,000 eggs per kilo of body weight but there is no guarantee that all or any of those eggs will be viable so to increase the chances of a good fertilisation rate usually two males and one female will be used when spawning. Using a clean tank filled to a depth of around ten inches with fresh water, and with spawning ropes draped across it, will provide the right environment to trigger the parent fish to spawn but once spawning has finished, the parents must be removed as they will do their best to eat as many eggs as they can!

Fish eggs are highly susceptible to fungus but a standard dose of malachite green in the spawning tank, after the parents have been removed, will ensure that they stay as fungus free as possible and will give them the best chance of developing.

Gentle aeration and a steady trickle of fresh clean water will provide a comfortable environment for the newly hatched Koi fry, although for the first few days after hatching, no food is needed as the fry hatch without a mouth and continue to develop by absorbing the remains of their egg sack. For the first few days of life they use a sticky pad on the top of their heads to stick themselves to anything they can find – spawning ropes, the sides or floor of the tank whilst they undergo this short transitional stage. The rate of development depends upon the temperature of the water and the warmer the water, the faster they develop. Usually after about three days from hatching, the fry develop a mouth and swim to the surface to take their first gulp of air which they force into their swim bladder and which provides them with the buoyancy that will enable them to move through the water hunting for food and evading potential predators. It is at this point that they are ready to be moved into a mud pond.

Historically, ornamental Koi were a by-product of the Carp that were bred for eating by the rice farmers in the Niigata region in Japan. They were an ideal form of polyculture alongside the rice because they could be grown in the mud pond water reservoirs that were used to feed the rice fields. It’s this availability of mud pond space that holds the key to the success of the regions farmers as breeders’ of Nishikigoi. So why is this mud pond space so important? Well, in order to produce good quality Koi, you need to ensure that as many fry as possible survive to a point where their colours can be seen and their potential assessed. The mud pond gives you the space to do this and, if managed properly, also provides an environment where the natural flora and fauna that are essential to a young Koi’s development can also thrive. It is important that a mud pond used for growing Koi fry is of a size and depth that can be easily harvested as if it isn’t, proper selection for quality cannot take place. Mud ponds have to be managed very carefully to make sure that they provide the ideal environment for Koi year after year and if they aren’t, detritus and bacteria can build up to a degree which becomes harmful to the fish and after a few years of use the productivity of a pond can deteriorate to a degree which makes it unsuitable for raising Koi fry.

We drain and dry our mud ponds each year which helps to provide a surface we can walk on without sinking into when we harvest and which stops any sludge building up on the bottom of the pond. Once the pond is filled up with water, it will undergo a cycle of algae growth and bloom whilst the water finds its natural balance. Sometimes some management is needed to help things along but generally each pond will cycle in its own way and should give the perfect environment for the rotifers and daphnia to grow and which provide the first weeks food for the young fry when they are transferred to the mud pond.

After this first week, the fry are ready to be fed with a high protein food which helps to supplement their natural diet and which will enable them to grow at their optimum rate. After around five weeks, they will have reached approximately one inch in length and will be ready for harvesting and selection.

Selection is the next key stage in producing Koi as without this the quality of the Koi produced would be very poor. We harvest between 30,000 and 50,000 fry from each mud pond at first selection and we sit and look at each and every fry to assess whether it has the potential to develop as a good representation of its variety. Only the best are kept and in doing so we help to ensure that those we keep do not become overcrowded and outcompeted for food by faster growing but less attractive Koi. We usually keep around ten percent or less of the Koi harvested at this stage which means that the vast majority are rejected as we do not consider them to be of a good enough standard to grow on further. The fry we choose to keep are then returned to the same mud pond and grown on for another 4-5 weeks before being harvested again and the numbers reduced to about one third.

This selection process goes on throughout the life of the Koi that we breed and grow on our farm and it is this process that ensures that the Koi that we produce are of the highest quality.

At 32 months old, this Shiro Utsuri has been through seven selection processes – each time we carry out selection we assess the body shape, skin quality, balance of pattern, contrast and the long term potential of each Koi. Some Koi are kept to develop further and others are sold and continue to improve in the care of their new owners. Many of these Koi make it onto the show circuit and visitors to this year’s BKKS National Koi Show will be able to see several examples of Koi bred at Cuttlebrook Koi Farm in the show vats.

So, the reason why breeding Koi is not as simple as it seems at first glance is that the spawning process itself is just the first step in what is quite a complex process. The science behind mud pond design and management are key features to the success of any Koi farm and the selection process is something of an art form which has to be mastered over time. When you look at the fish that you see in the show vats at this year’s National Koi Show, please take a few moments to consider the years of experience and care that have gone into producing these precious few Nishikigoi.

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, 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.
  • 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.
  • 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.
  •  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.
  • 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.
  • 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.
  • 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.
  • 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.
  •  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.
  • 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 Range Of Varieties

We breed a number of varieties of Koi each year and use our many years of experience to select the very best.

Hundreds Of Awards

We breed the finest Koi (Nishikigoi) in the UK and have won hundreds of awards for their owners over the years.

Online Or In-Person

You can buy the Koi we breed direct from us by visiting our farm in Oxfordshire, or you can order online.
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