When Do Koi Spawn In The Garden Pond?

Last updated on October 23rd, 2023 at 08:33 pm

Koi are one of the noblest and also most expensive ornamental fish for the garden pond. At the latest when the time for spawning has come, the males and females can be recognized. Unfortunately, for certain reasons and without human help, Koi offspring usually do not work out as hoped. Creating optimal conditions and protective measures for successful reproduction is not difficult at all.

Spawning season

When the temperatures constantly rise above 20 degrees Celsius, the garden pond often shows a lively activity of the Nishikigois. As a rule, the so-called spawning game begins in June, sometimes already at the end of May. Thereby the males (milters) can be recognized as these, because they chase the females (rogners). This means that the female, which has become rounder due to her eggs, swims in front, and the male follows behind. Their activity usually goes far beyond normal. They often jump out of the water like small dolphins and dive in again. It is not uncommon for them to land sporadically on the edge of the bank and die there without help to get back into the water. If your koi are jumping around “merrily”, it can be assumed that spawning season exists.

When Do Koi Spawn In The Garden Pond?

Note: Koi usually spawn only under certain conditions because they are very sensitive to water quality, food and generally their habitat. Thus, reproduction may take years to occur


Only healthy koi that are given plenty of space and swim in water quality that is optimal for them will spawn, although not necessarily every year. The beginning is made by a high quality koi food, which strengthens the animals and promotes organ functionality. Additionally, suitable places to spawn should be available. Otherwise, the females could suffer from a so-called spawning jam, which usually has health consequences. The following water values also form the basis for successful reproduction:

  • pH value between 7.5 and 8.5
  • KH-value above 5 °dH – carbonate hardness additionally stabilizes the pH-value
  • GH-value above 5 °dH (total hardness)
  • PO4-value lower than 0.035 milligrams per liter (phosphate makes thread algae useless)
  • FE-value lower than 0.2 milligrams per liter (iron promotes plant health and consequently oxygen formation)
  • Cu-value less than 0.14 milligrams per liter (too much makes koi sick)
  • O2-value at least 8 milligrams per liter (without sufficient oxygen restrictions in egg formation, spawning and fertilization)
See also  How To Safely Secure The Garden Pond?

Tip: The water values should be checked by measurement at least every ten days from early spring and corrected if necessary if reproduction is desired in the current season. This can be done quickly with quick tests from the specialized trade

Protective measures
To prevent the koi from injuring themselves through their exuberant actions or even jumping out of the pond, it is advisable to take appropriate protective measures:

  • Stretch a net over the pond (also prevents birds from feeding).
  • Replace sharp-edged, porous plant baskets
  • Refrain from pruning aquatic plants under water (sharp cuts could result)
  • Enlarge narrow passages at the edge of the pond so that koi cannot get stuck.
  • Sloping spawning brushes in shallow water areas attract koi to spawn and reduce rummaging through “brush”.
  • Spawning and fertilization

For spawning, koi move to the shallow water area. Here, the males poke the flanks of the females with their mouths to get them to spawn. A female can lay up to 1.5 million eggs. The eggs are usually fertilized by several males, provided they are present in the pond. Only between five and ten percent of the eggs have a chance to develop because, among other reasons, they stick together irrevocably into clumps immediately after the first contact with water and not every egg is accessible for fertilization.

Recognizing spawning

Spawning usually occurs on the stems and leaves of aquatic plants and preferably on reeds located in shallow water. Here, after spawning, the so-called spawning cords can be seen. They are whitish-yellowish, as large as the head of a pin and roundish in shape. In addition, an unpleasant odor is usually formed by the fish sperm, which can become even more pronounced when the offspring leave the eggs and open spawns remain.

See also  How To Settle Newts In The Garden Pond

After spawning

When the koi have completed their egg-laying and fertilization, there is a general state of exhaustion among them. They behave conspicuously quiet to recover from their exertions. This is the time when the uninvolved koi and other fish, as well as other pond and shore dwellers such as newts and frogs, will eat the eggs. The affected females and males eat them slightly during the recovery period.


If eggs are still present after the pond dwellers have been starved, the koi offspring hatch after about three to four days. They sink to the bottom of the pond. If they survive there, development proceeds as described below:

  • First two to three days: consume protein and fats from their yolk sac.
  • Larvae: about five millimeters in size and transparent
  • Subsequent formation of swim bladder and pectoral fins – horizontal swimming possible
  • Rise to the water surface
  • From 3rd day on color pigmentation begins
  • From day 7, formation of the dorsal fin – larvae between 12 and 14 millimeters in size
  • Fin formation completed around day 13 – recognizable as small koi – can eat like adult fish

Note: Until they grow into a juvenile fish, they are still in danger from predators. Especially at the water surface, they are a perfect victim also for various birds

Protective measures

To prevent predation on the eggs after spawning and to significantly increase the chances of successful reproduction, the koi eggs and later larvae should develop outside the garden pond in a certain protected area. The respective instructions explain what koi lovers need for this and how to proceed:


  • Aquarium or tub
  • Malachite green oxalate (for prevention of various diseases and especially against fungal growth of koi eggs)
  • Water/aquarium heater
  • Aeration/oxygen pump
  • Special growing food
  • According to experience, a mixture of the following has proven to be effective
  • Boil egg yolk, mix with pond water and let it run into the tank
  • Freshly hatched or frozen brine shrimp (Artemia salina) (feed chopped up)
  • Koi food from the specialized trade
See also  Pond Water Foams: What To Do With Foam On The Pond?

Instructions implementation:

  • Fill container with pond water
  • Add malachite green oxalate and mix well
  • Insert pump
  • Check pond/water plants for eggs, remove them and put them into the tank
  • If spawning brush was used, remove it and place it in the water tank
  • Turn on heater and set to 20 to 22 degrees Celsius (if temperatures drop below 5 degrees Celsius, eggs will die)

Instructions for breeding:

  • Carefully remove spawning substrate after hatching (deteriorates water quality due to contamination).
  • If the larvae swim, start feeding them
  • Feed five to seven times per day at water temperature between 20 and 22 degrees Celsius
  • Check water values daily, especially for ammonium and nitrite (cause the offspring to die quickly)
  • Regular water changes – pond water is still ideal (ensure correct temperature)
  • After four weeks, weed out fish that are too small and/or crippled
  • Change food to koi food, but grind it first
  • After about three months feed koi food in small pellets
  • From a size of five to seven centimeters release of the young fish in garden pond possible


  • James Jones

    Meet James Jones, a passionate gardening writer whose words bloom with the wisdom of an experienced horticulturist. With a deep-rooted love for all things green, James has dedicated his life to sharing the art and science of gardening with the world. James's words have found their way into countless publications, and his gardening insights have inspired a new generation of green thumbs. His commitment to sustainability and environmental stewardship shines through in every article he crafts.

Leave a Reply

Your email address will not be published. Required fields are marked *