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.
Fry in the spawning tank
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.
Transferring the fry
Fry in transport tank
These Kohaku 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!
Moving fry from the transport tank to the selection tanks
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. This Kohaku spawning was divided amongst two ponds and so what you see here is just half the number of fry from one just one female brood fish.
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.
Fry being released back into the mud pond
We have seven 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.