One of the most exciting and rewarding parts of owning goldfish can be seeing them give birth to a new generation.
Successfully breeding your goldfish shows you have taken good care of them.
And it gives you new baby fish to look after!
While it is possible for goldfish to reproduce in a tank, a lot of factors need to be right for this to happen.
It’s up to you to ensure that your goldfish have the conditions that encourage them to breed.
In this article, we look at how goldfish mate and the ideal conditions for mating.
How do fish mate?
Fish mate in lots of different ways. Goldfish mate by chasing each other until the female goldfish releases her eggs.
The male goldfish then releases his “milt”, which fertilizes the eggs.
Assuming the eggs don’t get eaten, baby goldfish will hatch around a week later.
What conditions do goldfish need in order to mate?
To encourage your goldfish to mate, you will first need a stable, well established and properly cycled tank. This tank should be easily large enough to house two adult goldfish.
The tank should be well planted and should contain at least one male and one female goldfish aged at least three years.
While younger fish can theoretically reproduce, female fish under the age of three are much more likely to become “egg bound”. This leads to eggs that fail to hatch. Even worse, it can potentially cause the death of the adult fish too.
The temperature of the water is one of the most important factors when it comes to breeding goldfish. It’s something that you will need to manage to produce the right breeding environment.
First, keep the tank temperature at around 64 degrees F for four months. Then, slowly warm the tank over the course of a couple of weeks to a temperature of 70-74 degrees F.
This slow rise in temperature will make your fish think it is breeding season.
When are goldfish ready to mate?
Mating behavior in goldfish is very distinctive. Once you know the signs, you will have no problems spotting it!
The male goldfish will develop small, white spots along their gills (these can often be mistaken for signs of disease, so look carefully!).
At the same time, the female goldfish will become fatter and more rounded.
The male goldfish will then chase the female around the tank.
The aim of this is to encourage the female to release her eggs. The mating “dance" of goldfish is tiring and they will chase each other nearly to the point of exhaustion!
This usually goes on for several hours and may also include the male nipping at the female’s tail and fins.
For obvious reasons, this behavior is often confused with fighting.
Goldfish egg release and fertilization
Eventually, when the female becomes so tired that she cannot continue the chase, she will release her eggs. Many of the eggs will stick to the walls of the tank and to the plants.
The male goldfish will then fertilize the eggs by releasing his “milt” (the goldfish version of sperm) into the water.
This can make the whole tank look cloudy, but don’t worry, it’s perfectly normal and you should not perform a water change.
Fertilized goldfish eggs
Healthy fertilized eggs should be clear in color.
Whereas unfertilized eggs will often develop fungus, which turns them white. Remove any white, unfertilized eggs from the tank, in order to avoid polluting the water.
Once the eggs have been fertilized, it is entirely possible that the goldfish will eat them! To prevent this, you should consider moving the fertilized eggs into a tank of their own. Alternatively, section off the eggs from your main tank so that the adults cannot get to them.
The holding area for the eggs should be shallow so that the water pressure remains low. The flow of water filtration should be very gentle in order to avoid harming the eggs and fry once they hatch. You don’t want eggs and baby goldfish getting sucked into your filter!
Goldfish egg development and hatching
A temperature of around 70 degrees F is ideal during their first five days. After this, you should drop the temperature to 64 degrees F for seven days.
At around four to five days after the eggs have been fertilized, you will begin to see growth inside them! This will appear as a small black spot in the center of each egg.
By day seven, these black specks will begin to hatch. You’ll start to see tiny goldfish sticking to the tank’s plants.
Goldfish only develop their full color as they age, so all newborn fry will appear black or dark gray. And they will be very tiny!
At this stage, you will be able to see the yolk sack that provides nutrition to the growing babies. Once the fry have consumed their yolk sacs, they will become much more mobile and start searching the tank for more food.
Unfortunately, fry often die due to a lack of food during this important stage of development.
You should therefore invest in food designed for fry, such as liquid food or very finely crushed flake food.
You can also feed them tiny pieces of hard-boiled egg yolk shaken in water until it’s almost dissolved. This diet should continue until the fry are large enough to eat full sized pellets and flakes.