First selection

This article was first written for and published by Koi Carp Magazine in 2008

Breeding Koi is as much an art form as it is a science and so to do it successfully you must grasp the basic scientific principles behind the elements that make a good fish farm and combine that with the art of Nishikigoi (the highest quality Koi).

What exactly is the “art” of Nishikigoi breeding though? It’s recognising the potential of a Koi from a very early age and ensuring that only the best quality Koi are grown on. This process starts at “first selection” (the Japanese call this sembetsu) when the baby Koi are just 4 – 5 weeks old and are harvested from the mud pond for the very first time.

From the moment the eggs are released from the female Oyagoi (parent fish) it is the skill of the breeder that provides the right environment for as many of the eggs as possible to hatch. Whilst a female Koi can produce between 100,000 – 120,000 eggs per kilo of body weight, not all of the eggs produced will hatch. This can be for a variety of reasons, for example they may be over ripe or unfertilised. The aim of the breeder is to provide the right environment for as many of the eggs as possible to hatch and then, once that has been achieved, that as many of the fry as possible survive to one inch and make it to first selection size. Breeding koi is initially pretty much a numbers game – the more that you can produce to one inch, the greater choice and chance you have of finding those few special Nishikigoi. Once hatched, the tiny fry spend a few days developing until they are ready to swim up and take their first gulp of air. This first gulp then goes into their swim bladder giving them buoyancy which means that they are fully functioning and are ready to go out into the mud pond.

The four weeks leading up to first harvest is crucial as the environment in the mud pond determines the growth rate, health and survival rate of the Koi in it. The more Koi you can grow to first selection size, the greater your chance of finding the few absolute crackers that go on to win awards at Koi shows.

The harvest usually starts early in the morning (rain or shine!) so that the rest of the day can be devoted to selection and the chosen few Koi with the most potential can be returned to the mud pond to be grown on further at the earliest opportunity. We use a drag net which stretches from one side of the pond to the other and which is deeper than the depth of the water in the pond. The net has lead weights on the bottom to make sure that no fish can escape under it and it has floats running along the top. With one person at either end of the net, it is carefully stretched across the pond and then slowly, and with great care, drawn down the pond until both ends can be brought together at one point on the opposite bank of the pond. The net is then gathered up so that all the fish are trapped.

The Koi are then scooped into a pan net and transferred as quickly and smoothly as possible into a bucket containing a small amount of water. This bucket is then passed up the bank and the Koi are gently placed into the waiting transport tank which has oxygen gently bubbling in it.

These fry are, on average, about 2.5 cm in length but some can be smaller than this and others, much bigger. It is important to harvest the fry at this size as if they are left in the pond any longer, the larger Koi will start to eat the smaller ones. Remember, the quality of the Koi is not determined by its growth rate and it is usually the larger and less desirable Koi that end up eating the more attractive smaller ones!

Once all the Koi fry have been transferred into the transport tank, they are then taken the short distance to the selection tanks. Once again, the pan net is used to gently place the Koi into a bucket and then they are transferred into a net suspended in a holding tank which is filled with fresh water and lots of air. The pond is then harvested a second time and whereas the first harvest might catch 30,000 – 50,000 fry, the second one usually catches just a few hundred. 

Once the fry have been transferred to the first holding tank at the back of the picture, the long and arduous process of first selection takes place. What we actually do is use a pan net to scoop up a few fry from the holding tank at the back, then suspend the net in water in the centre tray, and take out any fry we want to keep to grow on further. The Koi we are keeping are placed into the centre tray and the koi we don’t want to keep are placed in the front tank. At first selection size we usually try to keep not more than 3,000 fry from each spawning to grow on for a further month and if there are in excess of 30,000 fry in the pond to start with, that’s a maximum of just 10 per cent. At this stage we are looking for Koi with no deformities, good body shape, good skin quality and a balanced pattern. Ideally we don’t want Kohaku with full red heads or red fins. The hi (red) on Kohaku of this age is a pale orange and not nearly as obvious as it is on more mature Koi. We have to look very carefully at each and every Koi to determine whether it is a keeper or not. When breeding Kohaku you get every possible combination of red and white which means that we get a lot of all red fish (benigoi or aka muji) and a lot of all white (shiro muji) Koi. Then there are lots with poor pattern. Many of these Koi may be considered “pretty” but our aim is to breed good quality Koi and in order to maximise the potential of those few special Koi that we keep, we must be careful only to keep the very best. Mud pond space is valuable and if the chosen few are to achieve maximum benefit from it then we mustn’t keep any more Koi than is absolutely necessary.


Here you can see the special few that were kept from that one harvest of Kohaku – just enough to fill the bottom of the bucket. It usually takes us two days to carry out first selection and this is what we have to put back into the pond at the end of the day. It’s not easy to see any pattern on them at this age but you can see the good skin quality shining through on many of them. Most of these Koi will only be grown on for another month and then, once again, they are harvested and only 1,000 will be returned to each nursery pond to be grown on until the end of the summer.

We have 13 nursery ponds in all that we use for rearing fry throughout the summer months and where we have used two ponds to grow the results of just one spawning, the keepers from both ponds are put back into just one pond. By doing this we firstly maximise the potential of the first spawning by giving the fry as much pond space as possible and then after first selection has taken place, we are left with a “spare” pond which we can then drain down and used for a late spawning. When we drain the pond down we usually have a couple of hundred fry that managed to escape the net when the pond was harvested and so these are all removed to make sure that none of them are still in the pond when it is re-filled and new fry added. The whole process of first selection then starts again on a whole new pond full of fry.

There’s a lot more to breeding Nishikigoi than many people are aware of and this is just a small glimpse of what it takes to produce those few small precious Koi that make it into the show vats and your pond. In the next issue we will be harvesting the same Kohaku fry for second selection and we will show you how they have changed in just one month.

Second selection

This article was first written for and published by Koi Carp Magazine in 2008

5th May is “Boys’ Day” in Japan and it is also the time when traditionally, the Koi spawning season starts. This is a tradition which we have also followed most years and this year was no exception. One of the parent sets that we spawned on 5th May this year was Kohaku and we used a female from Hoshikin and two males that we bred ourselves and which came from a Momotaro and Matsunoske cross that we did a few years ago.

After spawning, the eggs take about three days to hatch and then a further three days for the fry to swim up and take their first gulp of air. After this has happened they are ready to be released into a mud pond where they are grown until they are around 2.5 cm in length and ready for first selection. At first selection we keep around 10 per cent, usually around 3000, baby Koi to go back into the mud pond for about another month before we harvest them again. It is this second harvest that this article follows.

This is very much a family business and whilst I am usually stuck in the office dealing with enquiries and all the boring paperwork, I do get involved when it comes to harvesting and selection. Selection is at the very core of our business and the decisions we make, about what to keep and what to reject, will affect our business for years to come. Each new parent set will produce slightly different offspring and Mark and I both use our years of experience at selection to predict how the baby Koi are likely to develop. Our youngest son Bryn, who is 11, is very keen to be involved in the business too and helps out around the farm when he can so that he can learn every aspect of farming Koi. Today, Bryn pitched in to help with the harvest which left me free to take photographs! Of course, I can’t continue without mentioning Mark Griffiths who has worked for us since he began helping out on Saturdays at the age of 15 and has worked full time for us for almost 18 months now. Over the years young Mark has become a key member of our team and is very much like part of the family.

Early in the morning at the start of August Mark decided that the Kohaku were ready for second selection. In our first article we showed how when harvesting a mud pond the net is stretched from one side of the pond to the other and slowly dragged from one end to the other. Over the years we have developed a technique that ensures the well being of the Koi that we harvest and makes sure that we catch as many as is possible at each harvest. When the net is being pulled up the bank of the mud pond it is important to make sure that the baby Koi do not get caught in the folds of the net. Mark (Davis) stays in the water, keeping the lead weights along the bottom of the net as close the ground as possible as it is pulled in. Mark (Griffiths) slowly pulls the top of the net which floats on the surface of the water in, at the same time, whilst Bryn takes the lead line from his father and pulls it, and the middle of the net, onto the bank, helping to make sure that the net is kept as wide and flat as possible.

These Koi are then transferred, using a pan net, into a bucket and placed gently into the transport tank. Even this process is carried out with the greatest of care and here you can see that as Bryn places the Koi into the tank, he isn’t pouring them out but is releasing them slowly by inverting the bucket so as to cause as little stress as possible.

The Koi are carried in the transport tank back to the selecting tanks and then a second harvest of the same mud pond is carried out. This is a good way of gauging the effectiveness of our harvesting technique as if we’ve done the job properly the first time we won’t catch very many second time round!

It’s already clear to see the difference in size between the Koi in this harvest and the last time they were harvested a few weeks ago. They are now 5 – 7.5 cm in length and some are even bigger! There are far fewer for us to select through than there were at first harvest and instead of taking us two long days to sort through them all, it can be comfortably done in just one day.

We are looking for good body shape, good skin quality, a white nose and tail and good contrast between the red and white as well as a balanced pattern. The difference in growth rates between Koi from the same spawning can be quite remarkable and it is apparent amongst these keepers. It is not our aim however to keep the faster growing Koi as growth rate has nothing to do with quality and it is quality that we are aiming for. Amongst them you may spot some Tancho Kohaku which are also produced when breeding Kohaku. These are actually quite rare and to find one with a perfect Tancho spot even more rare. Such a Koi, with good body shape and skin quality, is unlikely to be sold small and can command a high price when they do eventually go up for sale.

Here is a picture of the Kohaku that we kept after the first harvest and also a picture of some of the keepers from the second harvest using the same bucket. As you can see, they are much bigger now and the colour is deeper and the pattern easier to see.

After this second harvest was carried out we returned around 450 to the mud pond and the remainder were re-graded and moved to a sales tank. Each year our selection process gets tighter – the less Koi that we put back into the mud pond, the better the growth rate is likely to be. We have to find a balance between optimum growth rate and quality. We would rather keep a smaller number of higher quality Koi, that will have the opportunity to grow well, than to keep a higher number of less promising Koi to make up the numbers.

When we are carrying out selection, people always ask us what we do with the ones that we don‘t keep. Well, the answer is simple, each time we carry out selection on a pond of Koi, the ones we don’t keep are sold. Basically, we don’t have enough space on the farm to grow on every Koi that we produce and so we have to choose those that we feel have the best prospects for the future to grow on. Those that we sell are simply those for whom the future is not so certain in terms of development. It doesn’t mean that they aren’t nice Koi just that they are less likely to become a show winner than the ones that we keep to grow on. As a hobbyist, you could spend a reasonable amount of money on a selection of baby Koi and take the time to grow them on to see if any of them turns into something special, or you could spend the same amount of money on a much larger Koi that we have grown on and is that price because it is special.

Each Koi on the farm goes through a selection process at least twice a year until the day it is sold, so for a Koi to make it past two years of age and to still be growing on here, it must be something really special! This year we had a total of around 80 Koi that were two and three years old at the start of the summer growing on in one of our mud ponds – that’s 80 Koi chosen from over 1 million that made it to first selection size. That’s a lot of selecting and some very special Koi!

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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