How Do Goldfish Mate? (Age, Behavior, Process)

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With varying sizes, colors, patterns, and body shapes, goldfish is one of the many aquarium fish bred selectively.

But do you know how goldfish mate and breed? Have you seen a mating goldfish?

how do goldfish mate

If you have a goldfish or are planning to have one (even if you have no plans of breeding it), read this article because sooner or later, and whether you like it or not, your goldfish will become sexually mature and ready to mate.

Ideal Goldfish Age for Mating

Initially, goldfish reach sexual maturity between 225 and 233 days of rearing in a tank and will spawn at year one. We do not recommend mating and breeding at this stage since the eggs produced are small and relatively few.

The ideal age for goldfish to mate and breed is between their second and fourth years. By this time, the eggs produced are of the right size and number. The size and number of eggs will depend on the species of goldfish.

If you breed old goldfish, though they still can mate, the eggs produced are relatively large, and the occurrence of unfertilized eggs and deformity of fry is high.

Differentiating Male and Female Goldfish

Even for experts, it is hard to tell the gender of a goldfish if they are young. The manifestations will only come out when they reach sexual maturity.

In identifying the gender of your goldfish, do not rely on a single indicator. Rather, using multiple indicators will guarantee you of the correct sexing.

Body shape

In general, male and female goldfish have different body shapes.

Males have smaller, thinner, and more streamlined bodies. For females, since they produce eggs, their bodies are larger and rounder. During the breeding season, the tummies of female goldfish will swell on one side making them asymmetrical in appearance.

Be cautious in using body shapes in differentiating males and females. This indicator does not apply to some species of goldfish. For example, the Ryukin goldfish (whether male or female) has a naturally round and thick body.


Newbies use fin swaying to determine gender. They believe that the fins in males wave and females don’t.

This belief is accurate, and science can explain it.

Taxonomically, the fins of a goldfish are a good indicator of gender, and their prominence tends to side with the males.

Male goldfish fins are longer than their female counterparts. Specifically, males have pointed pectoral fins, and their anal fin is closer to the caudal fin.

Body Features

There are features of a specific body part prominent to a gender.


Exclusively occurring in males, tubercles are small white spots. It primarily appears on the gill cover, and in some cases, on the pectoral fins, scales, and face.

In male goldfish with the right age, the tubercles become prominent only during breeding season. However, the white spots can become permanent if your goldfish is old and has experienced several breeding seasons.

Caution: While tubercles are exclusively for males, not all male goldfish will develop white spots during breeding season. Look for other indications to come up with a conclusive sexing.

Anal Vent

The anal opening in goldfish is called a vent. When the vent is round and protruding, it indicates your goldfish is a female. The protrusion of the female vent is more pronounced as the breeding season approaches.

For males, their vent is concave, narrow, and elongated.

Midline Ridge

The midline ridge is a protruding line between the back of the pelvic fins and the anal vent.

In females, the midline ridge is non-existent or unnoticeable, while it is evident in males.

Sex Ratio in Goldfish Mating

At least one female and one male are needed for breeding to occur.

However, the 1:1 ratio will not maximize the fertilizing potential of males. A single male can fertilize more eggs than what is being produced by a single female.

We recommend 2:3 or two females paired with three males. In this way, the chances of having more fertilized eggs are high.

Conditioning for The Breeding Season

In the wild, goldfish mate and spawn from late spring to early summer.

Since we have a global readership, we decided not to mention specific months as these seasons vary per country. Furthermore, some countries have limited climate conditions, like the wet and dry seasons.

Nonetheless, the temperature change from cold to warm water triggers mating. Warming by 2ºC is considered an effective trigger.

In a tank setup, we are fortunate that we can control the settings and mimic the changing of the seasons in the wild.

Here are some steps to simulate and prepare your goldfish for mating.

Provision of Protein-Rich Food

Timeline: 6 months before mating and onwards

Your goldfish should have a good amount of fat long before they mate and spawn. You can do this by giving foods rich in protein. Aside from commercially available feeds, you can supplement them with earthworms and bloodworms.

You need to condition your goldfish with high-quality foods since mating and spawning require a lot of energy.

By the way, can you imagine a malnourished and underfed goldfish?

Mimicking Late Spring Waters

Timeline: 4 months before mating

After two months of food conditioning, you can now simulate the arrival of spring waters by adjusting your water temperature to 64ºF (18ºC).

Make sure that this specific water temperature is maintained for four months. You can prevent temperature fluctuation by using an automatic thermostat controller.

Addition of Live Aquatic Plants or Spawning Mops

Timeline: 3 weeks before mating

Aside from producing oxygen, live aquatic plants serve as spawning grounds. It is where freshly released eggs are attached.

Consequently, you can add an artificial spawning mop. If you want to customize and make your own, you can do this by tying several strings of synthetic yarn. Either place it in the tank floating or standing, as long as it has a vertical orientation.

You must do this before the next conditioning step since, from then on, the “do not disturb” sign is up.

Warming the Waters

Timeline: 2 weeks before mating

At this stage, your goldfish is well conditioned, and you need to simulate the changing of the season to trigger mating. You can do it by warming up the water between 68 to 72ºF (20 to 22ºC).

Do not disturb your goldfish from this time on. The process of mating can happen anytime soon. Disturbing your goldfish at this stage may not lead to successful mating and spawning.

Practical adult question for you (not for the goldfish): Do you want to be disturbed while mating?

Mating Process of Goldfish

Mating Process of Goldfish

In chronological order, here are the processes involved in goldfish mating. And by the way, please do not expect copulation, as goldfish have a unique way of mating.

The Courtship Dance

Courtship is a prelude to mating, and with goldfish, it is in the form of chasing.

During courtship, the male goldfish chases the female. He constantly pursues her day and night. The courting resembles a dance where swimming mixes up with sudden twists and turns, especially at tight corners.

Courtship can last for a couple of days. It is exhausting for the male and female goldfish, and this is where your food conditioning comes to work.

Male Ramming

During the chase dance, males bump the females once in a while. It is very exhausting for the males since he needs to swim hard for them to speed up and ram their body to the female.

Aside from ramming, males will also nip on the female’s fins.

It is only during the breeding season that ramming and nipping are not considered signs of fighting. These are natural responses that overwhelm your goldfish.

Egg Laying

The main reason males are ramming is for the females to release eggs. It is their natural way of squeezing out the eggs.

We, humans, can assist the males and facilitate the egg release in females through hand squeezing. You can do this by pressing and putting a little pressure on the female’s bulging tummy.

However, if unsure, do not squeeze and allow the male to do its function.

Since goldfish eggs are sticky when released, they are usually stuck in plants or at the spawning mops you installed weeks before.


Once the eggs are released and attached to a plant or any surface, the males will stop chasing the females and release their milt – a white-colored reproductive juice comparable to semen.

As a result, your water can become cloudy. Do not do anything since the milt will coat and fertilize the eggs upon settling.

If you don’t see males releasing milt even if the eggs are already in place, you can help them by doing the hand squeeze and doing the same thing as you did with the females.

Things to Do After Goldfish Mating

While continuing to care for your goldfish, your attention by this time should focus on the eggs.

Search for Fertilized Eggs

The eggs that were laid and milted are tiny and spherical. Depending on the species, the eggs of goldfish are colored anywhere from white, to yellow, and orange.

Color will also be your indicator if the eggs are fertilized or not. Unfertilized eggs will become cloudy white, while fertilized eggs will become transparent after a few days. This is also the time that a tiny black spot will appear on each fertile egg. Eventually, this dark marking will become the eyes.

Transfer of Spawning Mop

Leaving behind the unfertilized egg is mandatory, as it will become food for your goldfish. However, leaving behind the fertilized egg is optional.

You can leave the eggs with their parents in the same tank they were born in. However, the likelihood of being eaten is possible as goldfish may eat their eggs (whether fertilized or not).

For a higher chance of survival, you can transfer the plants or the spawning mop containing fertilized eggs to a separate aquarium. It will become your hatching tank.

It only takes three to seven days for the eggs to hatch into fry and become baby goldfish.

Do not expect all fertilized eggs to hatch. Only 80% will hatch, and 30% will reach adulthood.

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What Is the Frequency of Mating in Goldfish?

If the conditions are conducive, goldfish will do multiple mating and spawning in a single season.

Since we can control the temperature in the tank, mating and spawning can be extended. However, it is not advisable since it will drain out the energy of your fish.

Goldfish breeders practice up to three mating sessions in a single season. In this way, the fish is not frazzled and still produces good quality eggs and milt.

Can Goldfish Change Their Gender?

Sequential hermaphroditism is happening in fish. When a fish switches from male to female, it is called protandry. On the other hand, protogyny refers to the switching from females to males.

In goldfish, both protandry and protogyny are absent. Upon hatching, the gender of a goldfish is fixed and will never reverse.

How to Avoid Unwanted Goldfish Breeding?

With sexing, only place goldfish with the same gender.

Focus on other factors if you’re unsure about the sex. Do not condition your goldfish as if you’re inducing them to mate.

You can continue giving them high-protein foods. However, make sure that your water temperature is stable. Remember that a sudden increase in temperature triggers mating.

If the inevitable happens and your goldfish has mated and released eggs, do not do anything. Leave it as is. Sooner or later, your matured goldfish will eat the eggs.

What Is the Difference Between Goldfish Fighting and Mating?

Chasing and fin-nipping are signs that your goldfish is either mating or fighting. But if you see how the indications occur, you can differentiate what fighting and mating are.

If chasing is persistent, with the occasional nipping and body ramming, it is a clear indication of mating. In the case of mating, the males chase the females. This mating behavior can last for a few days.

However, if chasing is occasional and nipping is more pronounced during the chase, it indicates fighting. After the pursuit, if both goldfish parted ways, their encounter can be associated with playing.


Conditioning your goldfish to mate takes time and effort. But it is rewarding.

While you can buy baby goldfish in a pet shop, the feeling of doing the preparations yourself and producing baby goldfish, in the end, is priceless.

You can consider it your trophy for your hard work. And finally, people will be looking up to you and may elevate their perception of you from a newbie to a breeder.

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