How Long Are Koi Fish Pregnant For

How Long Are Koi Fish Pregnant For? (Answered)


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For Koi breeders, Koi pregnancy is something that many are interested in, as these fish can produce hundreds of eggs at a time. If you’re thinking about breeding koi, it’s important to understand the process of koi pregnancy so that you can be prepared for what to expect. Here’s what you need to know about koi pregnancy and childbirth.

Koi reproduce by spawning, which means that the female releases her eggs into the water and the male fertilizes them. Spawning typically occurs in the spring, but it can happen at other times of the year as well. Once the eggs are fertilized, they will hatch within a few days.


During the pregnancy, the female koi will often become more aggressive, and she may even chase away other fish. This is normal behavior, and it’s nothing to be concerned about. However, if you have other fish in your pond, you may want to consider moving them to another location during the spawning season so that they don’t get harassed by the female koi.

Once the eggs hatch, the fry (baby koi) will spend the next few weeks hiding amongst the plants in your pond. They won’t start to venture out into open water until they’re a few months old. At this point, you can start feeding them small bits of food.

As your fry grows, they’ll eventually start to resemble their parents. At this point, you can begin to sex the koi fish so that you can separate the males and females. Once they’re fully grown, you can then start to breed them if you’d like.


Koi pregnancy and childbirth is a relatively straightforward process, but it’s still important to be prepared for it. By understanding what to expect, you can ensure that your koi are healthy and happy throughout the entire process.

Do Koi Fish Become Pregnant?

Koi fish do not become pregnant like mammals (like humans) do, they do not give birth to babies. Koi are oviparous fish which means they form and carry unfertilized eggs in their bodies making them look pregnant (bloated) and then the eggs are dropped in the water during spawning season for male fertilization. The fertilization of the eggs doesn’t necessarily require contact between a male and female Koi fish, it can happen if there are multiple Koi of both sexes in the same body of water as the eggs will be fertilized by whoever happens to be swimming by when the female drops them.

How Long Are Koi Fish Pregnant For?

Koi pregnancy can last for up to two weeks before the female is ready to lay her eggs. As said earlier, Koi fish do not technically become pregnant, they instead carry eggs and then lay the eggs which is the explanation for the bloated stomach of a female Koi fish. The length of time that the female koi is carrying the eggs will generally determine how many eggs she will lay, with a longer gestation period resulting in more eggs.


Koi are oviparous, which means they lay eggs instead of giving birth to live young. After the female is ready to lay her eggs, she will release them into the water where they will be fertilized by the male.

The average gestation period (time from being fertilized until the eggs are dropped) for Koi is about 2-4 days but this can vary depending on the water temperature. The fertilized eggs will then hatch and the fry (baby koi) will emerge. It takes about two weeks for the fry to fully develop and be ready to swim on its own.


A male Koi can store sperm inside their bodies for up to 6 weeks which means they can fertilize eggs multiple times per season the same way female Koi fish can lay anywhere from a few hundred to tens of thousands of eggs at a time.


During pregnancy, it is important to keep an eye on your female koi fish as they can be more susceptible to disease and parasites. It is also important to make sure that the water quality is high as poor water quality can lead to problems with the development of the fry. Once the fry is hatched, they should be kept in a separate tank until they are large enough to be added to the main pond.

How Long Do Koi Fish Carry Their Eggs?

Koi fish carry their eggs for about two weeks before they hatch. After hatching, the fry, or baby fish, will then spend another two weeks in the egg sac before they are able to swim on their own.


The fry is often kept separately in special nurseries for several weeks until they are big enough to be released into the main pond.

How Do You Know If A Koi Fish Is Pregnant?

If you think your koi fish might be pregnant, look for these 8 signs:

  1. A sudden change in appetite – either eating more or less than usual
  2. Behavior changes – Increased aggression towards other koi or fish in the tank
  3. A change in swimming habits – either being more active or less active than usual
  4. Females may start chasing males around the pond
  5. Change in coloration – The gravid spot, a dark patch on the underside of the fish near the vent, may become more pronounced
  6. The abdomen may appear swollen or bloated
  7. Increased mucus production
  8. Nipple-like growths on the underside of the fish

If you notice any of these signs, it’s possible your koi fish is pregnant. However, the only way to be sure is to take your fish to a vet or experienced koi breeder for inspection.


Looking after pregnant koi fish is not much different from looking after any other kind of koi fish. Make sure they have plenty of clean, fresh water to swim in and a healthy diet. You may want to increase the amount of food you’re feeding them slightly as they’ll need extra energy to lay their eggs.

What Does A Pregnant Koi Fish Look Like?

Pregnant koi fish have a distinctive rounder belly than their non-pregnant counterparts. The Gravid Spot, located on the underside of the female koi near the tail, will also darken in color and become more pronounced. These two physical changes are caused by the enlarged ovaries of the pregnant koi as they prepare to lay their eggs.

What A Pregnant Koi Fish Look Like
What A Pregnant Koi Fish Look Like

In extreme cases, the belly of the pregnant koi may be so large that it presses against the fish’s swim bladder, causing it to swim awkwardly or float upside down. However, this is not harmful to the koi and will resolve itself once the eggs are laid.


Pregnant koi are also more susceptible to stress and should be protected from sudden changes in temperature or water quality.

By taking good care of your pregnant koi, you can ensure a successful spawning and help preserve this beautiful species for generations to come.

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