When breeding Koi there is a difference between a breeder who is spawning his Koi, a hobbyist who is trying to breed and a hobbyist whose Koi breed by themselves.

Quite often Koi keepers will wake up to find that their Koi have spawned – there will probably be a lot of bubbles or foam on the surface of the pond and there will be a strong smell of ammonia. It is important to be aware of these indicators because once a spawning has occurred a high level of ammonia will be present in the water. One must then do a water test to check that the ammonia level is still within acceptable levels. If it is too high and it is not corrected one can end up with fatalities. Where the test indicates that it is too high, a water change needs to be done and a dechlorination product, such as AC++ Bio elite, should be used to take out the chlorine and chloramines. If you wish to try and hatch the fry, be careful when changing the water to avoid losing them.

In South Africa spawning generally occurs from mid-spring to late summer, with most spawning occurring in September and November. When female Koi are ready to spawn they look fuller and heavier than normal. Ideally the best age for a female Koi to be spawned is around the age of four and older – females older than five 5 years produce eggs that are more fertile and also bigger in size, which favours stronger fry. Females are sometimes able to spawn in the beginning of the season and then again a few months later. The danger of breeding at a young age is that the parent Koi can lose its colours and patterns.

Male Koi develop small whitish tubercles or nodules on their pectoral fins and gill plates when they are sexually ready, and those areas of the body feel rough. They are usually ready from the age of two years. The younger males can be used for spawning every two weeks but older males have optimum fertility potential if used at greater time intervals.

Firstly you need to select two or three male Koi that are sexually ready and place them in a ‘porta pool’ or separate Koi pond with a plump female. Make sure the ‘porta pool’ or pond is well aerated and that the media you have selected is suspended from the walls of the pond. There is a variety of different spawning media that can be used: Spanish moss, artificial grasses, natural plants, vegetable sacking and shade cloth (torn into strips) are all suitable. The Koi deposit the semi-adhesive eggs onto the spawning media.

The spawning process is quite violent – the Koi can get damaged and end up with bruises, cuts and torn fins – so it is unwise to use your show quality Koi for breeding if you are inexperienced. It is advisable to cover the breeding pond with a net to prevent the Koi leaping out of the pond during spawning. The female Koi releases from about 100 000 to 500 000 eggs and then rests with her head pointing down when she has finished. The Males too will show that they have lost interest. Remove the parent Koi from the breeding pond or else they will start to feed on the eggs.

Change approximately 35% of the water in the breeding pond, taking care not to lose any of the eggs, which will still be attached to the spawning media. After 40 hours the bodies of the fry will have formed in the eggs. After another five to seven days the fry hatch by breaking out of their eggshells. They are normally transparent and cannot swim at this stage. They have a sticky pad on their heads, which they use to attach themselves to the side of the pond or to the spawning materials.

The fry’s first food sources are the yolk sacs that hang from their bellies and when these are depleted they will be relying on you to provide food. Hard-boiled chicken egg yolk can be placed in a stocking and swirled around the pond. Daphnia and brine shrimp larvae, as well as crushed Koi pellets, can also be fed to them. After two weeks you can feed them powder food. After three weeks the fry will be around 5 mm long and should be showing some colour, normally yellow or white.

If you don’t want to go to the trouble of setting up a separate breeding pond, you can place spawning materials in your Koi pond but in all likelihood you will lose quantities of fry to the appetites of the adult Koi. Feeding daphnia and brine shrimps to the fry gives them a better chance of survival however they may even survive without being fed, as long as your pond is not immaculately clean. A few weeks later you may find a few babies will have survived and will hopefully grow quite rapidly into larger Koi.