Breeding Goldfish: Goldfish Egg Hatching!

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Goldfish pair finally laid some eggs in my fish tank at home.

After quietly observing eggs for five days, they hatched!

In this article I have some photos of our goldfish eggs from day 0 till hatching.

Day 0 – Goldfish Eggs Found!


So my goldfish pair (male and female, bronze fantails) finally laid some eggs.

Having faith that at least some of eggs are fertile, I isolated them from parents goldfish and waited for them to hatch.

What to do When You Find Goldfish Eggs?

Parent goldfish will eat their own eggs, so eggs need to be quickly separated from goldfish.

Goldfish eggs I found were attached to aquatic plants, so I moved plants to a new bowl with eggs adhered.

I used a plastic container, with some water that was taken from the main goldfish tank.

How long to Hatch?

How long goldfish eggs take to hatch, depends on the water temperature; in Japan people say there is “sum of 100C rule”.

That is, when the sum of temperature (in degree Celsius) multiplied by the number of days (after eggs being laid) exceeds 100, eggs will hatch.


For example, at around 69oF(20oC), 20oCx 5 = 100, so it will take approximately 5 days.

If the water temperature is 25oC, then it will take approximately 4 days.

This is said to be the general rules, but of course the water temperature fluctuates during a day and you can never be exactly sure when eggs hatch…

As for the eggs I found, they hatched sometimes between day 4 ~ day 5 after being laid.

The water temperature was 21-22 oC.

2 Days After Goldfish Eggs Being Laid


While goldfish lay many eggs, some of them will be unfertilized, unviable eggs.

Only about 40-50% eggs will be fertilized at best, in a usual fish tank environment.

After two days, fertile eggs will remain clear. You might see some embryo development in the egg.


In the photo above, you can almost see faint – grey colored eyes developing inside the egg.

The spine of the baby fish is also barely visible…. ?


On the same day, the egg above is developing slightly faster than others.

You can already see eyes (black circles) on the left side of the egg quite clearly.

In contrary to fertile eggs, unfertile unviable eggs will turn completely white and opaque.

You will see white molds quickly growing on the egg.


Like in the photo above, infertile egg is very easy to identify by the opaque white look.

White hair-like thing on the egg is mold growth.

When you find these unviable or “dead” eggs, you need to remove them so that the mold will not spread to affect other healthy eggs.

I used small forceps and scissors to remove these white dead eggs as soon as I see them.

3 Days into Goldfish Egg Development

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Fertile eggs are continuing to develop.

Black eyes are visible in most viable eggs and the body of fish is also darkened and visible.

4 Days into Goldfish Egg Development


Baby goldfish inside eggs are visible now.


Sometimes they move inside the egg, like they are rotating to change their body position.

They look like they are ready to hatch anytime!

5 Days Later… Hatch!


Five days after eggs were laid…. they have hatched!

I found small needle-like goldfish hatchlings on the wall of the plastic container they were in.


Goldfish hatchlings do not move or eat on their first day.

They have egg-sacs on their bellies and those egg sacs contain some nutrients for their first day.

They usually start moving and feeding from the following day after they hatch.

Goldfish hatchlings are so small…. really like a small moving needles!

So my goldfish egg hatched and now have second-generation goldfish babies! 

I will report how they are growing in another article to come…


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