This article was first written for and published by Koi Carp Magazine in 2007
When people see images of mud ponds being harvested in the autumn it is invariably nisai (koi in their second year of life) and older that are being lifted from the pond. At this time of year however it is also time for the tosai, or koi in their first year of life, to be harvested.
By the time autumn comes around these tosai, bred earlier in the year, will have been harvested at least twice before. Each time their numbers will have been drastically reduced in order that those returned to the mud pond for further growing on are of the best quality and get the best chance of survival. At Cuttlebrook Koi Farm this process is carried out in exactly the same way as it is in Japan and by the time Autumn arrives, the number of koi in each pond has been reduced by careful selection from around 30,000 – 60,000 fry down to around 1,000.
At Cuttlebrook there are seven nursery ponds which are dedicated to taking Tosai through their first months of life. There are six ponds that are 20 metres by 15 metres and which hold approximately 300 tonnes of water and a further nursery pond which is 13 metres by 40 metres and holds 500 tonnes of water. Each pond has a net stretched across it which stops Kingfishers, Ducks and Heron’s etc feasting on the vulnerable fry.
A further two ponds are dedicated to growing Nisai and older koi. There are two polytunnels – one being the main sales area and the other the breeding facility, and three further buildings comprising of the Quarantine House, Nisai House for taking Nisai through the winter months and Tosai House for taking Tosai through the winter.
Cuttlebrook Koi Farm
Two of the nursery ponds containing Sanke and Chagoi were harvested in September and the remaining five were harvested in the first three weeks of October. At each harvest, a drag net is stretched across the width of the pond at one end and is then carefully pulled down each side and across the other end. The two ends of the drag net are then pulled up onto the bank and the bottom of the net pulled up, completely trapping the koi. The net is then pulled in taking care not to trap any small fish in its folds. The transport tank waiting next to the pond has an oxygen bottle next to it allowing oxygen to be gently bubbled into the tank as large numbers of koi will quickly use the available oxygen in the water, particularly on warm days.
Shusui harvest – net being pulled in
Once the net has been pulled in, it is secured in place using metal pins and poles. This makes it easy to then catch the koi using a pan net.
Goshiki in the net in the pond
The young koi are removed from the drag net with a small pan net and then transferred to a bucket briefly, before being placed in the transport tank. Each pond will be harvested twice to ensure that as many koi as possible are removed from the pond before it is drained down.
Goshiki in pan net
After the koi have been transferred to the transport tank, they are then taken to the selection tanks for grading and sizing. The transport tank has a specially made net suspended in it which allows the koi that have been held in it to be removed easily and with the least amount of stress.
Shiro Utsuri in transport tank
From the transport tank, the Tosai are then moved into a net suspended in a holding tank ready for selection. Using a pole pushed under the net, the koi can be forced to one end making catching a few at a time easier.
Selection tank
A small number of koi are caught in a large pan net which is then suspended in a bowl of water. Each koi is carefully examined for deformities, body shape, skin quality and pattern and using a smaller hand net, appropriate to the size of the koi being selected, the koi are sorted into those that will be grown on over the winter and those that will be made available for sale. Any deformed or stunted koi are humanely euthanized.
Shiro Utsuri in selection net
The size of the koi that are harvested depends on several factors, the most important one being when they were spawned. If they were spawned early in the season then they will have been able to achieve a good growth rate. If they were spawned later in the season, they will be much smaller. Some varieties grow faster than others also. Another factor which can affect growth rate is stocking density.
These koi, all from the same spawning, were spawned early in the season. From this one spawning you can see Chagoi, Ochiba Shigure, Ginrin Chagoi and Ginrin Ochiba Shigure. The fastest growing ones are always the Chagoi!
Chagoi Tosai
These Goshiki, which were spawned at the same time as the Chagoi, have also achieved a good growth rate although have not grown at quite the same rate as some of the larger Chagoi. Whilst the depth of colour on varieties such as Chagoi tend to stay the same as they grow, on varieties of koi that have red, or hi, on them, the hi appears more orange on very young koi and will deepen as the koi grows and the skin gets thicker.
Goshiki Tosai
These Shiro Utsuri, whilst they were spawned at the same time as the Chagoi and Goshiki are quite a bit smaller. This is due to the variety itself not being particularly fast growing but also due in part to the very high survival rate in that particular pond meaning that competition for food was greater, leading to slower growth rates in general. These particular Shiro Utsuri show great promise as the white, or shiroji, on them is bright and the black, or sumi, is strong and deep. The pattern on Shiro Utsuri can change quite significantly over time.
Shiro Utsuri Tosai
These Hariwake were spawned several weeks later than the Goshiki, Chagoi and Shiro Utsuri and you can see that because of this, they are on average much smaller, although not that much smaller than the Shiro Utsuri. When breeding Hariwake other varieties that are also produced are Orenji Ogon and Platinum Ogon. One of the most important attributes of a good Hariwake is a good metallic sheen.
Hariwake Tosai
Lastly, these Shusui which were the last spawning of the season have only reached second selection size of 2-3 inches. Being a Doitsu, or mostly scaleless fish, a good “zipper line” along the dorsal ridge is desireable.
Shusui Tosai
On average, between 200 – 300 koi are chosen from each harvest to be grown on and the remainder are moved to unheated sales tanks. Those that are to be grown on are moved to a purpose built insulated building called the “Tosai House” where they spend the winter in water heated to around 23 degrees C. The Tosai House is 60 metres long by 9 metres wide and contains six tanks of 2200 gallons each.
Hot houses
Inside the tosai house
Goshiki in the tosai house
By the time the Autumn Harvest has been completed, just 2 per cent of the total number of koi bred this year will be kept for growing on. The koi placed in the Tosai house will then be resized and re-graded as they grow throughout the winter. Each time only the best quality koi will be chosen to be grown on and by the time spring arrives, a further selection takes place and, depending on what size each koi was when it entered the Tosai House, they should be between 20 and 35 cm in length on average and reduced in numbers through selection again to only 1000 fish. From this 1000, just 300 will be chosen to be grown on to their second year in the mud ponds over the summer. What this means is that from the 300,000 koi bred and grown to first selection size at 2.5 cm, only an amazing 0.1 percent are finally chosen to be grown on to be harvested as Nisai the following Autumn.
So, if you’ve ever wondered why good quality koi are so expensive, spare a thought for the amount of work involved in raising those few special koi. These koi are the very cream of the crop and Koi bred at Cuttlebrook Koi Farm have gone on to win 37 show prizes in 2007 alone, including Best in Size One at the BKKS National in June. The aim at Cuttlebrook Koi Farm is to produce the highest quality koi (or Nishikigoi as they are known in Japan) by following Japanese methods and selection techniques. It is this “Devotion to the perfection of Nishikigoi” that has led to Koi bred at Cuttlebrook Koi Farm being judged amongst the best in the country.