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How To Care For Koi Eggs The Right Way – 4 Key Steps & FAQs

Lindsey Stanton Profile Picture

By Lindsey Stanton

koi fish eggs on a brick

If you have been breeding Koi fish and have gotten your female to successfully lay eggs, or if you just happen to find your Koi fish laying eggs, you might want to know how to take care of them. Now, some people might not want their Koi fish to mate and have young.

After all, rearing fish fry can be expensive, time-consuming, and fairly difficult, too. On a side note, caring for Koi fish eggs themselves is not actually that difficult. However, Koi fish are quite expensive, so if you find yourself with some Koi fish eggs, you might want to take care of them and hatch them.

Anyway, how to care for Koi eggs is what we are here to talk about right now. We’re also going to spend a bit of time talking about how to care for Koi fish fry until they reach a decent size.

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The 4 Steps to Caring for Koi Eggs

1. Spotting Koi Fish Eggs

What Do Koi Eggs Look Like?

First off, you will have to be able to spot Koi fish eggs to take care of them. They tend to be very tiny, only millimeters in diameter and they tend to be a soft brownish color. Also, they are translucent.

So, they should not be too hard to identify, but if you don’t know what to look for, you might not see them, or you might mistake them for some kind of aquarium scum. If you have been purposefully breeding your Koi and setting up mating tanks, seeing eggs should be no surprise.

However, if you have not been purposefully getting the Koi fish to breed, and it all happens by chance, if your female Koi fish are getting big bellies, they are probably getting ready to lay some eggs.

How Many Eggs Do Koi Fish Lay?

Koi fish will usually lay eggs all over the tank or pond at random. A 2-pound Koi fish can lay up to 100,000 eggs. In fact, for every 2 pounds or 1 kilogram that a female Koi fish weighs, she can lay up to 100,000 eggs.

So, a 10-pound Koi fish could potentially lay up to 1,000,000 eggs. However, this is rare, and only some of the eggs will be viable.

2. Removing the Koi Fish Eggs from the Tank Or Pond

koi fish farming
Image Credit: Donny Agung Prasetyo, Shutterstock

If you do want to care for the eggs and raise the fry, you will need to remove the eggs from the main tank. If you do not remove the eggs, chances are that the adult Koi fish will eat most or all of the eggs. Fish tend to do this in general, not just Koi fish. Ideally, you should gather the eggs before they hatch.

Adult Koi fish seem to be more interested in eating fish fry after they hatch, rather than eating them in their embryonic state. If it happened by chance, you will probably end up gathering the eggs by hand or with a little net.

However, if you were planning on mating your fish and raising young, you should have used a spawning rope. This is a special kind of rope net contraption that fish breeders use, especially Koi fish breeders.

For some reason, female Koi fish will lay their eggs on or along these spawning ropes, which the eggs stick to. If you have a spawning rope, all you need to do is remove it from the tank and place it in the nursery tank.

Koi Eggs Turning White

Now, keep in mind that not all Koi fish are viable. The ones that are translucent and slightly brown are good, but any eggs that are milky and white will not be viable. These will either never hatch or the Koi fish fry will hatch with birth defects that will render them incapable of long-term survival.

3. The Incubation Pond

Now that you have transferred the eggs into an incubation or nursery pond, you need to make sure that the water conditions are ideal for proper Koi fish egg development and hatching. This is easier than it sounds.

If you have a spawning rope with lots of Koi fish eggs on it, you should use nothing less than a 100-gallon aquarium and make sure that the top of the spawning rope is no more than 2 inches under the surface of the water.

Water Conditions (pH / Hardness)

In terms of the water conditions, the water should be between 68 and 71 degrees Fahrenheit. Any colder or hotter than that, and most of the eggs will probably not hatch, or they will be born with birth defects.

In terms of the pH level and the water hardness, keeping them at a medium level will be fine. Neutral water works well, but a pH level of around 7.5, or slightly basic, is best for their survival. Other than that, the most important part is oxygen.

How Long Do Koi Eggs Take To Hatch?

The Koi fish eggs need oxygen, which you can supply to them using a simple air stone or two. If all goes to plan, the Koi fish eggs should hatch in about 4 or 5 days.

4. Taking Care Of Koi Fish Fry

koi fish in pond
Image Credit: Vital safo, Shutterstock

So, taking care of the Koi fish fry is pretty important too. After all, whether you want to keep them or sell them, they need to grow to a decent size before you can begin doing anything with them.

Water Quality

In terms of the water quality, it needs to be spectacular. Just like with human babies, Koi fish fry immune systems are not fully developed yet. This means that they are susceptible to stress and disease.

Just make sure to keep the water at a pristine quality. In other words, you want to have a really good filter with lots of mechanical, chemical, and biological filtration capacity. Moreover, the water should be around 70 to 75 degrees Fahrenheit.

Their little bodies can’t handle the cold quite as well as adult Koi fish, so keeping the water a little warmer than it needs to be for the adults is ideal. When it comes to the pH level, around 7.2 to 8 is fine but no higher or lower than that.

Feeding Koi Fish Fry

The other important part is feeding. For the first few days, Koi fish fry will be sustained by the egg yolk which they ate while still in the eggs. However, after the first 3 days, you will need to start feeding them yourself. Some people actually go with real egg yolks, as the nutrients in egg yolks are ideal for Koi fish fry.

However, you can also go out and buy specialized Koi fish fry food as well. Their mouths are really small, so feeding them anything substantial in the first 3 or 4 weeks just won’t work. After their mouths have gotten a little bigger, you can start feeding them solid foods.

We have covered our top food picks for adult Koi fish over at this article here.

a koi pond
Image Credit: Pixabay

Live Or Freeze Dried Food?

Now, some people go with live foods, but these can be full of parasites and disease, which young Koi fish fry won’t be able to handle well. Some freeze-dried foods are best as the freeze drying process will kill off most parasites and diseases.

Freeze-dried krill, daphnia, and baby brine shrimp. Heck, even some hard-boiled eggs work just fine here. Once the Koi fish start getting really big, you can move on to normal Koi fish food.

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Commonly Asked Questions

At what age do koi start breeding?

Koi fish will usually start breeding at around 3 years of age, give or take. It depends on the specific fish and the environment, although 3 years is usually about right.

Interestingly enough, most Koi fish will stop breeding when they reach 6 or 7 years of age.

How can you tell if a koi is male or female?

One way to tell apart male and female Koi fish is by their body shape. Male koi will usually be fairly long and slender, whereas females can be a bit shorter and rounder, especially when it comes time to breed.

Another way to tell apart males and females is by the fins. Male Koi fish will have a pointed and solid color pectoral fin. During mating season, male Koi will also develop tubercles, little white growths on their heads and pectoral fins.

Utsuri Koi fish
Image Credit: koifish, Shutterstock

What time of year do koi lay eggs?

For the most part, koi laying eggs is dictated by the temperature, and they will usually begin to do so when temperatures are between 65° to 70°F.

In most cases, this means that Koi will lay eggs in late May or early June. In other words, late spring or early summer is when most Koi fish lay their eggs.

How long does it take for koi fish to grow?

Koi fish, for the most part, will actually continue to grow until they are dead. It’s going to take between 4 and 5 years to get a Koi fish to a mature Koi, and then another 4 years or so until they reach champion Koi size.

Therefore, you can count on a Koi taking about 10 years before it reaches its full size, although they will continue to grow slowly as they age after that, but not much.

koi fishes in the pond
Image Credit: NatalieStamer, Pixabay

Do Koi stop eating when spawning?

Sometimes Koi may stop eating while spawning, simply because they are too busy to eat. However, there is no rule or part of biology which dictates that Koi have to stop eating during spawning.

How do you know if a koi fish is pregnant?

The only real way to tell if a female Koi fish is pregnant is by examining the belly. If she looks more bloated than usual, quite round, and kind of chunky, like she has eaten a sack of marble, then a Koi fish is pregnant.

Now, keep in mind that koi fish technically are never pregnant per se, as they are not livebearers. They are egg-layers, so technically they never get pregnant.

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As you can see, taking care of Koi fish eggs is not actually that difficult. Sure, it takes a bit of time and a bunch of money too. However, the reward for caring for these Koi fish eggs is quite substantial.

If you plan on selling the young Koi fish, you stand to make a fair amount of money, which is always nice. Heck, you can even keep a few and expand your collection as well.

Featured Image Credit: Mr. Piyapong, Shutterstock

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