Spawning brushes: how to set them up for koi breeding
Spawning brushes mimic the dense plants on which koi carp and goldfish lay their eggs. They make spawning easier and let you remove the eggs before the adult fish eat them. Here is when and how to use them.
— Key points
- When: from April to July, once the water rises above about 18 °C.
- Where: at the edge of the pond, just below the surface, in a calm area.
- How many: 3 to 4 brushes for a good spawning surface.
- After spawning: take the brushes out and place them in a separate tank.
When to put the brushes in?
Spawning depends on water temperature and day length. It usually takes place between April and July, when the water reaches about 18 to 20 °C. The tell-tale signs: males chasing a female with a rounded belly, often early in the morning after a lively evening.
You need at least one adult female and two males. In a sparsely planted pond with no suitable spawning surface, spawning may not happen at all, or the females may injure themselves on stones.
How to fix them
- Hang the brushes by their hook from the edge of the pond, or tie them to a floating support.
- Place them just below the surface, side by side or stacked on top of each other.
- Choose a calm area, away from the pump return.
- Leave a little space around them so the fish can swim round.
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Aquaforte spawning brush 130 x 15 cm
Large spawning brush offering a generous spawning surface in koi ponds. Live price and instant add to cart:
After spawning: protecting the eggs
Spawning lasts several hours and most of the eggs stick to the brushes. The adult fish eat the eggs: as soon as spawning is over, gently lift the brushes out and place them in a separate, aerated tank filled with pond water at the same temperature.
- The eggs hatch in 3 to 6 days, depending on the temperature.
- White, opaque eggs are unfertilised and go mouldy: a small number of them is normal.
- At first the larvae stay attached and live off their yolk sac.
Feeding the fry
As soon as the fry swim freely, they need very fine food: infusoria, very finely crushed hard-boiled egg yolk, then brine shrimp nauplii and powdered fry food. Keep them separate until they are too big to be eaten.
Read also
To find out what comes next, read How do I feed my baby koi (fry)? I have babies in my pond....
READ THE ARTICLELimiting breeding
Not every birth is wanted: an overstocked pond quickly becomes unmanageable. The brushes can also be used to remove the eggs and prevent overstocking: leave them to dry in the sun, then hose the brushes down before storing them.
Kit to limit overstocking in ponds - fish trap and food
Fish trap for catching surplus fry without draining the pond. Live price and instant add to cart:
Small fish net 88 cm - Oase
Net for moving fry and young fish without injuring them. Live price and instant add to cart:
Getting your koi ready before the season
Brushes are useless if the fish are not in good condition. Preparation starts as soon as temperatures begin to rise. Resume feeding gradually with a quality food suited to the water temperature, and keep an eye on nitrites: water quality affects spawning, and poor water can stop it altogether.
Check the group as well. A koi carp must have reached maturity to spawn: fish that are too young will not take part. Look at your females, which are rounder, and your males, which are slimmer. A thermometer keeps you from putting the brushes in too early or missing the moment: in May, the water temperature can sometimes climb fast over a few sunny days.
Spawning is a physical affair. The males push the female for hours, and fish sometimes get injured. Remove any sharp objects from the pond, and keep an eye on exhausted females afterwards. The water may turn cloudy and foam after spawning: increase aeration and check nitrites over the following days.
Successful egg incubation
The separate tank makes all the difference. A large, clean tank filled with pond water keeps the same water chemistry and avoids a temperature shock. Gentle aeration is enough: the bubbles should circulate the water without shaking the brushes. Keep the tank out of direct sunlight and night frost, and cover it with a light net if birds or insects can get to it.
During incubation, avoid handling the brushes. Only remove whatever is decaying if the water turns cloudy, and replace a small part of the water with pond water. As soon as the larvae have let go and are swimming, take the brushes out, as they would otherwise become a source of pollution.
Growing on and sorting the fry
Feed very small amounts several times a day and siphon off the leftovers: in a small volume, uneaten food quickly spoils the water. Choose a pellet size suited to the size of the fish. Not all fry grow at the same rate, and the biggest can eat the smallest: sorting them regularly reduces losses.
Set yourself a realistic goal. A single spawning can produce far more fish than your pond can hold, and not all of them will have attractive patterns. Keep a small number of fish, and plan what to do with the others before hatching. Never release fish into the wild. For goldfish, see Breeding goldfish in a pond, and on the question of fish farming, Can you breed fish in a garden pond?
Put your brushes in on an evening when the forecast announces a rise in temperature. The morning after a warm spell is often the morning of spawning. Watch whether the fish are chasing each other along the edge, and get your tank ready.
Hikari Plankton Early 400 gPellets for fry from 4 to 10 mm that do not dissolve in water.View productAquaOxy 500 OaseQuiet air pump, 500 l/h and 8 W, with two air stones, for a tank or pond up to 5 m³.View productSuperFish pond thermometerTo monitor the temperature and put the brushes in at the right time.View product
Frequently asked questions
— Do the brushes work with goldfish?
Yes, the principle is the same for all pond cyprinids.
— Why are my koi not spawning?
Water too cold, fish too young, no males, or no spawning surface. Poor water quality also holds back spawning.
— Can the brushes be left in all year round?
It is better to take them out outside the season: they collect deposits. Clean them and store them dry.
In summary
- From April to July, water around 18 to 20 °C.
- 3 to 4 brushes just below the surface, in a calm area.
- Brushes taken out after spawning, eggs in a separate tank.
- Very fine food as soon as the fry swim.
Sources and references
- Hands-on experience of Aquiflor, aquatic garden centre in Nodebais (Belgium) for more than 30 years
- Questions received by the Foudebassin.com customer service team
Last updated: 28 September 2026.
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