Breeding koi in a pond

I have been a koi keeper for five years now and I haven’t bought any koi for the last three years. My pond is approximately 3,000 gallons and has nine koi. They are all between three and four years old and range from 20cm to 45cm in length. Everything is running very smoothly at the moment, the filters are well matured, the fish feed well and are happy and healthy. I am now at the stage where I would like to take on a new challenge. I would like to start breeding my own koi but I’m not really sure how to go about it. I have read some books on the subject but I still feel as though I need a lot more information. Can you help me out?

It sounds as though you have a fine collection of koi that are ideal candidates for spawning. Assuming that you have a mix of both males and females, your koi will by now be sufficiently mature to spawn. There are a number of practical things you need to consider before embarking on the path of becoming a surrogate koi farmer. Furthermore, you should be aware of the limitations you are likely to face, which hopefully will temper your expectations. The koi that are in your pond will respond to environmental cues in the same way as career broodstock do in Japan, so where possible, to help you understand the spawning process, I will touch on some tricks that the professionals use when farming koi.

To breed or not to breed?

Now that you are looking to breed your mature koi, you will hopefully have taken into account the risks involved.

Many koi keepers do not wish their koi to breed, as the spawning event is quite stressful for koi. Unlike at all other times, koi are not graceful or reserved in their spawning behaviour. If males significantly outnumber ripe females then females in particular can become quite exhausted and physically damaged as the males drive and bash at the swollen females in their attempts to expel their eggs.

This can lead to loss of scales and permanent scarring and when I used to farm koi, I had regular contact with a number of koi keepers who wanted their females to be induced and stripped artificially to release their eggs in a controlled manner. Many of these females already exhibit damage from previous spawning activity. On the more positive side, you have the opportunity of increasing the number of koi in your pond, tapping into the genetic and biological potential of your own koi.

What makes koi spawn?

I am a little puzzled as to why your pond full of mature, healthy koi has not already spawned spontaneously in the preceding years. They are no more likely to spawn next year by you simply wishing them to do so. Once you have identified the key spawning triggers, you will have to intervene accordingly in order to stimulate a spawning response.

Koi spawn in late spring/early summer in response to environmental stimuli which signal that their environment will provide their fry with the physical conditions and natural food supply so crucial for their good growth and survival. Even though koi are in-bred selected descendants of wild carp species, they have retained this biological clock from their ancestors, and it is something we can capitalise upon when trying to stimulate them to spawn.

Two key factors that stimulate koi to breed are water temperature and day length (photoperiod). These stimuli work in tandem to influence when koi spawn. Water temperature will fluctuate at comparable dates from year to year, whereas photoperiod is far more consistent. I.e. We know that June the 21st will be the longest day each year but that temperature will fluctuate year on year and is not as predictable as day length (especially up in Lancashire!). The overall effect of these interactions means that koi will spawn at different times all over the country (or perhaps not spawn at all).

It is the increasing day length that has the greatest effect on maturing the female’s eggs, with water temperature having more of an effect towards the time of spawning. Koi are happiest to spawn at about 20 degrees C or on subsequent cooler mornings once these temperatures have been achieved. The final trigger for spawning may sound obvious, but once the females’ eggs are ripe, the factor that finally causes the eggs to be released and spawning activity stimulated is the presence of males. By keeping the sexes separate, commercial farmers can prevent spontaneous spawning events, but unfortunately, in your pond, you are likely to experience (or even miss) a spontaneous flock spawn.

Problems with a flock spawn.

Besides the risk of physical damage, a flock spawn immediately limits your productivity as a koi breeder. As soon as a female koi releases her eggs into the pond, there is a 30 second window of opportunity for the sperm (which are now heavily diluted in your pond water) to fertilise the eggs. After that, as the eggs swell by taking on water, the micropyle (small duct) through which the sperm will fuse with the female genetic material will close. This will lead to an overall drop in fertility rates, having a knock-on effect for the fry numbers.

A flock spawn also impacts upon the quality of fry produced. The specimen varieties that we stock in our own ponds are the product of crosses between similar koi varieties. The probability of achieving something similar in a spawning free-for-all in a koi pond is greatly reduced. So in realistic terms, you should aim at producing viable fry that you can grow on (irrespective of their livery). Don’t expect these fry to resemble any recognised varieties, as this can only really be reliably achieved by spawning known parents under controlled conditions.

Why are your koi not spawning spontaneously at the moment?

Having farmed koi for over 7 years, experience shows that you need to have complete control over all of the environmental stimuli to have a chance of being successful. By doing so, you can virtually guarantee a spawn. In a garden pond however, you have to accept the environmental conditions provided naturally, often with unpredictable results. The natural conditions will of course prove more difficult in the north of England, compared with the south. You can however, increase your chances of spawning by manipulating your pond’s temperature at 2 key periods in the calendar year.

Autumn-Winter. Koi that experience a cold period (4 Degrees C or below for 1 month) have been shown to spawn more reliably the following season. Ensure your koi experience 1 month of ambient temperature through the winter.

Spring-Summer. Once you have reset their biological clock to ‘zero’ (by giving them a cold period), you can now increase their chances of spawning by heating the pond from mid February onwards, achieving a minimum of 15 Degree C each day. Again, experience shows that if koi experience 1000 degree days (see Boxout), they are likely to spawn. This certainly works for professional carp and koi farmers who make this strategy the backbone of their farming husbandry.

Allowing your koi to experience 1000 degree days.

The water temperature is raised gradually, held at 15 degrees C and your koi are subjected to a lengthening photoperiod.

The golden rule in maturing females is to subject them to 1000-degree days. That is, 3 days at 15 degrees C = 45 degree days and so on. A tally of degree-days should be kept to ensure that at least 1000-degree days are achieved prior to spawning. Once achieved, koi are likely to spawn. Give them a final helping hand by bringing your pond temperature up to 23 Degrees C.

Spawning time.

Once your pond approaches the 1000 Degree Days mark, you can add spawning media (soft rope/woollen mops) onto which your koi will deposit their adhesive eggs. These can then be later removed as your koi will soon help themselves to the eggs (and later on – the fry).

Fry rearing.

Even for the professional koi breeder, raising fry is the most challenging part of farming koi. This is certainly the experience for most koi keepers that experience an unplanned spawn. The short notice does not allow sufficient preparation which means that many thousands of eggs will only become hundreds of fry. Ultimately only a handful of homebred koi will reach fingerling size. For this reason, if the hobbyist is keen to breed from their collection, they must provide the eggs and fry with suitable conditions to hatch and grow out in.

Quite paradoxically, the best environment for fry to flourish is in a green, unfiltered but natural pond, full of microscopic zooplankton. It is often resistance against such an ‘unsightly’ pond that results in only a handful of fingerlings being produced in the same pond as the broodstock. Stocking fry into ‘stew ponds’ is the method used by commercial koi farmers grow on their fry in both the UK and Japan. If you have any spare clay-based land, then dig yourself a fry pond; it will certainly increase your yield.

As an encouragement, it must be remembered that each year even commercial breeders produce many thousands of very poor, low-grade fry similar in appearance to those produced by accident in koi ponds each year. The difference being that the commercial breeders start off with many more and are able to cull hard, ensuring that only those fish exhibiting good characteristics make it to market. As koi keepers, we should be thrilled with any extra home grown koi that we can produce, being loathed to cull any of them.

So in conclusion, it is a little mystifying why your mature koi have not already spawned in your pond. As one of the key factors is water temperature (a likely limitation in sunny Lancashire!), by investing in a pond heater and using it wisely and strategically, your chances of spawning koi in your own pond will increase. However, be well aware of the risks and limitations involved. We should be realistic when trying to breed koi and raise fry in the same pond, being happy to see only a handful of fry reach 2-3″ in their first year, irrespective of their coloration or pattern which are likely to be disappointing. likely to be disappointing.

Kill blanketweed and string algae.