Koi Spawning. That magical time (or times) of the year when sexually mature koi do their part to propagate the species in the science experiment that is your pond or tank.

Except, maybe it’s not that magical.

At least, not for your pond or water quality if you aren’t actively trying to breed your stock and if you don’t have the facilities set up for it. In most instances, when breeding season happens, the filters in the pond simply can’t handle the amount of biology that happens in such a small amount of time.

Those enthusiasts that do breed their koi will move fertilized eggs out of the breeding pond or tank that the spawning happened into a separate facility (or nursery tank) so that they aren’t eaten by the proud parents (and anything else in the pond!) as well as to not overburden the tank’s filtration.

Although not as common, there are some instances where the female will spawn twice in a year. Females lay a huge number of eggs (with anywhere from 20,000-100,000) in a single setting. They can do it in stages, stopping to refuel on some of the eggs that they have just laid. In fact, up to 90% of the eggs that are laid can end up as dinner for other pond denizens.

Eggs are visible and are described as looking like tapioca pudding. The eggs will stick pretty much anything they touch, sometimes they even get sprayed out of the pond! Running your hand along the top and sides of the pond, you will feel the eggs. They will adhere to water plants, too.

Signs of Spawning

koi eggs after a spawnSpawning can happen anywhere from February through June when temperatures start to rise. Between 60-70ºF is optimal temperature.

But like all things in nature, there are those exceptions to set rules, and condition changes, like significant water changes (upwards of 20%), can cause a gravid female to speed up the egg release. It is why unexpected additional spawnings can happen.

The female will begin to nose potential breeding sites and egg attachment sites. You will also notice foam around active water features you might have or in your skimmer. The protein in the male’s sperm will give portions of your pond that just bubble bathed appearance, too.

The smell. The milt that the males produce has a strong, pungent odor that is unmistakable. Once you have smelled it, you won’t forget it. It is fishy and “pondy.” It usually lasts a couple of days. If the smell doesn’t go away, carbon can help with the smell.

Another dead giveaway is the antics that are going on in the pond. Ordinarily, there is harmony in the pond, but when the pheromones are in the air (or water), the males’ attentions are less than subtle and will chase the females around, nudge them and bump into them to try and get the female to release eggs into his milt.

Here’s a video of some of the behaviors that happening during spawning.

It can be advisable to net up during this period as it can get fairly animated during the process.

Koi Spawning and Water Quality?

Sheesh, spawning will tear up some water quality…
Had a spawning in my 960g pond. First for that pond. Boy the water quality went to s#*t quickly!.

— Tim Nye

There are biological ramifications of a female (or females) laying eggs and males milting in your pond. The change of water parameters can be pretty significant. And very quick. You might go to bed and wake up to a murky pond that has a characteristic odor that you might not have smelled coming from your water the night before.

Additionally, the protein from both the eggs and sperm can cause the ammonia levels to spike which can seriously affect water quality.  It can also negatively impact nitrite and to some extent the nitrate levels. It is why many enthusiasts will perform a water change the day of the spawn. For those that might not have the adequate filtration, bi-weekly water changes for the next 2-3 weeks can be helpful to get the water quality back into optimal parameters.


As I was saying earlier, Temp, change in chemistry, and I have heard but not sure how true it is, but Moon phases are also supposed to be a trigger point as well, and we have had a full moon. Some people don’t realize but Koi can scatter eggs in small spawns all during the years. Most simply go unnoticed. But when an all out spawning does take place there is so much discharge that the bio simply can’t keep up with the sudden change and water chemistry changes rapidly.  

— Larkin Baggett

Don’t fret when you have a spawn. Just be aware of what is happening in your pond and to your koi. Be aware that the females can be a little roughed up in the experience and monitor them a little more closely as they convalesce.

Being aware of what is happening and knowing how to account for it will make you better prepared to deal with spawning.

9 responses

  1. Jay Miles :

    I am interested in purchasing the 25 grab bag. Does the buy one, get one free apply here???

    These will be in an outdoor pond in Georgia. Will these spawn this Spring/Summer? If not what fish would I have to buy to get spawn at this time?

    today is Jan 3, 2017

    1. No, sorry, Grab Bag Koi are not included in the Buy One Get One Free sale.

      Also Koi need to be a minimum of 2 years old and about 10 inches or larger to spawn. So you would need to purchase Koi at that size, or have them in the pond for at least one full season before they were ready to spawn.

      Let us know if you have any other questions. Thanks.

  2. Diane HenaultTosi :

    I’m new to this hobby, fascinated with the pedigree. I am in the process of reconstruction of an inherited pond. Keep me posted if shipping to Florida is possible

    1. That sounds exciting! Shipping to Florida is certainly available year around. Feel free to visit our website and shop for some new additions to your pond. If you have any other questions, you may direct them to sales@nextdaykoi.com

      Thank you.

Leave a Reply

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