10. Breeding Spawning Koi Successfully

Having followed the previous 9 steps to successful koikeeping, the final step – koi breeding, can prove a contentious topic amongst koi keepers. There are those of us who want their koi to breed, taking from it a degree of satisfaction that our koi are so healthy and that the pond environment that we have created for them is so ideal that our fish actively spawn as a result. Indeed, because koi have likely been preparing for the spawning event for nearly a year, it shows that our pond has provided them with top quality conditions for many months.

On the other hand, some koi keepers do not wish their koi to breed, as the spawning event can prove to be quite a risk for their fish. Unlike at all other times, koi are not graceful or reserved in their spawning behaviour with koi keepers fearing the worst for their valuable koi that appear to be ‘fighting’ each other. If males significantly outnumber ripe females then all of the participating fish, but particularly the females, can become quite exhausted and physically battered as the males drive and bash at the swollen females to expel their eggs.

This can lead to the loss of scales or permanent scarring. Those koi keepers who do not want their females to spawn may opt for them to be induced and stripped artificially so that their eggs can be released in a controlled manner, forgoing the physical spawning behaviour.

For the sake of the final piece in this series on ‘Successful Koi Keeping’, we will take the view that for koi to spawn in a pond is a desirable experience, and a positive reflection on the husbandry they will have experienced in our pond. We will also briefly compare what we are likely to be able to achieve in a koi pond, compared to say a professional farmer who may employ more advanced techniques.

Just got to breed!

Irrespective of the genetic changes that may have taken place to the external features of our koi today, at heart, they are still physiologically carp and respond to the same environmental stimuli as their ‘wild’ ancestors. In this way, koi are just like any other fish in that they have an innate need to breed and to perpetuate their species; It is what they exist for.

Koi spawn in late spring/early summer in response to environmental stimuli which signal that their natural environment will provide their fry with the physical conditions and natural food supply so crucial for their good growth and survival. They respond to these same cues in an artificial koi pond.

When will my koi spawn?

Two key factors that stimulate koi to breed are water temperature and day length (photoperiod). These stimuli work in tandem to influence when our koi will 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 are not as predictable as day length. The overall effect of these interactions means that koi will spawn at different times all over the country. Koi kept in ponds in the south of the UK are more likely to spawn earlier than those in the north.

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. 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. In a back garden koi pond, this will result in a flock spawn (which in itself is likely to limit the success we could expect from our koi). Recognising the limitations (and risks) involved in a flock spawn, koi farmers prefer to segregate the sexes and limit their contact. In so doing, commercial farmers can prevent spontaneous spawning events and can manage their koi that will experience similar environmental stimuli to our own pond-bound koi but to greater efficiency.

How the professionals can do it.

Furnished with the above information, it is possible to manipulate koi broodstock in captivity to stimulate them to breed when required. Broodstock are separated into their sexes and brought inside after winter, having experienced a good summer’s feeding to ensure that quality eggs have been produced in their ovaries. The eggs for spawning this summer were laid down last summer after last year’s spawn. If a female is not carrying eggs by the winter then that fish will not spawn this year.

The water temperature is raised gradually, held at 15 degrees C and the fish are subjected to an artificial photoperiod, aimed to mimic mid-June at the desired time of spawning. This enables spawning to be carried out earlier than the fish would naturally do so.

As we saw in ‘Step 9 – The Koi Calendar’, 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. So long as the sexes are kept separate then even if this is exceeded spawning should not take place. This is why koi in the warmer south will spawn before their cooler, northern counterparts.

To prevent damage to valuable broodstock, the natural spawning activity is avoided by inducing females to release their eggs from the ovaries ready for stripping with a hormone injection. Males are given a similar injection to increase sperm production to an amount that can be collected.

The sperm and eggs from specific koi varieties can then be crossed, with a view to producing significant quantities of similar fish. These eggs are then incubated for approximately 5 days (again, depending on the water temperature) until they hatch. They are raised on freshly-hatched brineshrimp in hatchery tanks and then stocked out into daphnia-rich mud production ponds where they are eventually weaned onto a dry diet and culled on size, deformity and pattern.

Koi Pond Spawnings

Compared to the professional koi farmers, spawnings that occur in our own ponds often take us by surprise, putting us at an immediate disadvantage in that we will not have prepared suitable conditions in which to raise our fry. Consequently, even though we too may end up with many thousands of eggs, only a few hundred fry will result, and from those, a handful of fingerling (2″) koi. For this reason, if we are keen to breed from our own collection, we must provide the eggs and fry with suitable conditions in which to hatch and grow out. Quite paradoxically, the best environment for fry to flourish is 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 successfully raised when kept in the same highly filtered 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, and is something we should do to improve our chances of raising quality fry..

Limitations of a flock spawn.

A fundamental problem that we encounter during a flock spawn is our lack of control when selecting which broodstock to cross. This breeding free-for-all will have a knock-on effect on both the fertility rate and the varieties represented in the resultant offspring.

For example, a commercial breeder who has carefully been able to develop and select his broodstock, creating quite a stable bloodline over many years is more likely to produce a large number of fish true to that variety. This is unlikely to be the case with an unplanned flock spawn involving crosses between numerous varieties of varying bloodlines.

You’ve made it!

Even though the quantity and quality of fry that result from a pond spawning may be disappointing, spawning activity in your pond should be greeted as your koi’s appreciation and positive feedback as to the quality of environment that you have provided them. Breeding is the pinnacle of a koi’s existence, and should be regarded as one of the most fundamental thresholds that a koi keeper can cross; Evidence that as a koi keeper, you have indeed achieved koi keeping success.

Kill blanketweed and string algae.