Koi Spawning

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

Spawning 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?

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.

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.