May 22

Getting Smart With Identifying Between A Male And A Female Goldfish

It’s understandable as an aspiring aquarist to know the gender of your pet goldfish either for breeding purposes or when it comes to naming them. Do you really want to be calling your female goldfish “George”?

Additionally, fish keepers need to know the gender of the fish if they are trying to set up a single-sex population.

Meantime, AquaPlanets has this video on Youtube that shows you 5 Ways To Identify Male Or Female Goldfish.

Let’s continue with our topic. This article will cover a detailed walkthrough on identifying if a goldfish is male or female by noticing specific behavior signs and physical characteristics of a goldfish. So, without further ado, let’s dive in. 

The Difficulties You May Encounter

goldfish swimming

It’s true that gender identification isn’t as easy as ABC. Fish sexing is complex, and there is no foolproof method for sexing common goldfish. Many factors like species, physical characteristics, and behavioral cues come into play.

Sometimes, the goldfish forgo reproductive functions to survive if they don’t get appropriate nutrition, space, or clean water. In this situation, since it is unlikely a fish will show external signs of gender differentiation, you are then left with observing their behavior during the spawning season.

For instance, some male goldfish may not develop tubercles while some female fish might. Additionally, male goldfish may have protruding vents, unlike a female goldfish. Species also play a factor.

For instance, goldfish breeds such as ranchu or ryukin naturally have thick and round body shapes, making it impossible to differentiate between males and females correctly.

Goldfish maturity age is another way to know if the goldfish is male or female. Since gender differences are easily identifiable once the goldfish reach maturity, some male goldfish will reach maturity when nine months old.

At the same time, it might take three years for a female goldfish to fully mature.

Other difficulties may also include a goldfish’s general health. Goldfish usually do not follow typical spawning behavior if deprived of quality water and appropriate nutrition.

For instance, an unhealthy male goldfish may not develop tubercles, or a thinner, underfed female goldfish may be misidentified as a male goldfish. Hence, when it comes to sexing goldfish, it is best not to rely on only one sign.

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Goldfish Female or Male: Seven Ways of Sexing Goldfish

three goldfish swimming

Before identifying specific characteristics when sexing goldfish, you must know that goldfish are not sexually dimorphic until they reach adulthood. Dimorphism means physical characteristics to differentiate between the male and female sexes. 

The sexual maturity of a typical goldfish lies between 9-12 months of age. At the same time, goldfish found at the pet store are usually 2-3 months old.

    So, chances are, you won’t know their sex until sexual maturity is reached. Additionally, sexing goldfish is done easily during the breeding season due to pronounced changes.

    Now, let’s dive into how you can tell if a goldfish is a male or a female.

    1. Protruding Vents

      Goldfish have a vent (anal opening), an opening on their body that releases genetic material like eggs or sperm and waste. Female goldfish have a slightly protruding vent, meaning if viewed sideways, the vent may appear to be outwards.

      Whereas, in male goldfish, the vent is inward or flat. Only during the breeding season will the vent in a male goldfish raise slightly, which only a wary eye can notice.

      Another way of identification is by looking for a midline ridge. If possible, you can also look at the underbelly of the fish, where you will notice a raised line running from the vent to the back of the pelvic fin; chances are, it is a male goldfish.

    2. Behavioral Cues

      Goldfish’s behavioral cues may make it easier to differentiate between a male goldfish and a female one. For instance, male goldfish will often chase a female goldfish and nip at her back to stimulate egg release.

      Sometimes, a male fish may chase multiple female goldfish, and numerous males may chase a female goldfish. However, if you spot multiple males chasing a single female fish or tearing its fins, that’s a case of dealing with a bully, which must be dealt with by isolating the fish. Also, you must know that all goldfish interbreed. So, you can always add a divider to your aquarium if you want a pure strain of goldfish.

    3. Changing Body Shape

      When female goldfish are ready to spawn during the breeding season, they will plump up and develop around the abdomen to produce eggs. Sometimes the swelling is asymmetrical. It means the bulge is more visible on one side. 

      However, male goldfish generally have a streamlined and thin body shape that does not change when breeding. And will also develop light-colored, small bumps on their pictorial fins.

    4. Signs of Tubercles (Breeding Stars)

      One can spot visible differences in the pectoral fins of a male and female goldfish. For instance, in male goldfish, small white spots called tubercles may appear on their gill shields, on the scale of the body, and on the face.

      In males, breeding tubercles will only last during the breeding period. Males also have narrower and longer fins as compared to females.

      However, it’s important to note that not all males will develop tubercles which may lead to misidentifying the gender of your fish.

    5. Shape and Size of Fins

      The pectoral fins in male goldfish are longer, thinner, and pointed. However, female goldfish have shorter fins. Therefore, this identification method may not work if your goldfish species differ. For instance, veil tail goldfish genetically have longer fins. Also, important to note that male goldfish generally have more flowing fins than females.

      However, in fancy goldfish breeds, it’s challenging to identify the gender on the basis of fin shape. The long flowing fins look almost identical in both genders. In such goldfish breeds, you should instead look at the pectoral fins. The pectoral fins of males in these are usually longer, thinner, and feature a pointy tip. On the other hand, the fins of females are shorter, wider, and feature a rounded tip.

    6. Spawning Behavior

      Spawning behavior is another way to tell the difference between female and male goldfish. If you witness your goldfish spawning, you can easily determine the gender. Only females release a large number of orange eggs. Males will just tag along to fertilize the eggs. Female goldfish sometimes start releasing their eggs even while escaping from the males. That’s why you see all those orange eggs everywhere in your goldfish tank.

    7. Goldfish Swimming Momentum 

      You can also tell the difference by noticing their momentum in the tank. There are certain swimming patterns that are hard to miss. For instance, females often swim faster than males while trying to outrun their breeding “advances.” 

      Similarly, you will notice some goldfish that have become sluggish while swimming. These are probably pregnant fish. Males will easily swim faster than such sluggish goldfish. 

      Furthermore, male goldfish will often chase other males if no females are around. On the other hand, female goldfish will never chase other female goldfish. So, you can easily tell the difference between their genders on the basis of their swimming momentum in the tank.


    Identifying the sex of your goldfish is indeed not as straightforward as it seems. It takes time, skill, and patience to pick up on behavioral cues and physical characteristics to know the difference between male and female goldfish. 

    Additionally, it also takes practice to hold your goldfish still and long enough to examine vents, fins, midline ridges, and body shape. However, understanding sexual dimorphism and spawning behavior may make it easier for fish keepers and aspiring aquarists to tell if a goldfish is a male or female.

    Lastly, goldfish breed in warm water. Therefore, to reflect changes in season, you must alter your aquarium’s water temperature, or your goldfish may end up breeding or interbreeding all year round. 

    We hope now you know how to identify the gender in goldfish. Let us know what you think in the comments below. 

    Frequently Asked Questions (FAQs)

    Here are a few commonly asked questions people have when keeping goldfish or breeding them. Going through them will make things more straightforward when it comes to sexing goldfish or any peculiar behavior they may have.

    How long does a goldfish live on average?

    ANS:  Unfortunately, most do not know this, but goldfish can live up to 10-15 years. Some species may also live up to 30 years.

    However, goldfish need adequate space to swim, proper care, and nutrition to live long and not fall prey to depression and stress.

    Do goldfish ever fight?

    ANS: Goldfish are generally calm and friendly fish. However, on rare occasions, if you spot any fights between your goldfish, it is better to put a divider in the tank or get separate tanks before integrating them again.

    Can a goldfish change gender spontaneously?

    ANS: Some fish do change their gender spontaneously. However, goldfish cannot do so. A male Goldfish will remain a male throughout his lifespan, and a female will continue to lay eggs. 

    Are female Goldfish bigger than males?

    ANS: Mostly, yes. The female goldfish are somewhat bigger in size than the male goldfish of the same age. They also appear slightly heavier in the belly. However, the difference is hard to notice at a cursory glance. They’re so small that it becomes very difficult to distinguish their size. 

    How to make sure that I successfully breed goldfish? 

    ANS: Consider purchasing at least six young goldfish of the same specie at the same time. This way, there’s a better chance that you will get at least one goldfish of a different gender for your aquarium. Once you have the two genders in the fry, they can successfully breed. 

    What is the purpose of breeding tubercles?

    ANS: As the name suggests, breeding tubercle functions include species recognition, spawning, and breeding of females.

    How to differentiate between breeding stars and ich parasites?

    ANS: Breeding stars are small white dots formed neatly in regular patterns on the fish’s pectoral fin or face. They are often formed right before the breeding season.

    However, the white spot disease ich/ick so not form regular patterns and may vary in size. Before treating any disease, check in with your local veterinarian to avoid health issues. 

    How old does my goldfish need to be to tell if they are males or females?

    ANS: Apart from the physical differences that are visible between the two sexes. A goldfish must have reached sexual maturity and should generally be older than a year for one to tell if they are a male or a female.

    However, some goldfish species may show visible physical characteristics when they reach 2-3 years.

    What’s the ideal male-to-female goldfish ratio for an aquarium? 

    ANS: If you plan to keep multiple male fish in the same tank, make sure you have multiple female fish. Otherwise, it can cause tension and aggression in the males. They will start fighting with each other to breed with the lone female goldfish. So, the ideal male-to-female goldfish ratio for a tank is 1 male for two females. 

    Why is my goldfish sitting at the bottom of the tank?

    ANS: This is a common query among people, and the answer is not as simple. Goldfish are generally hyperactive and are always on and about doing something.

    So, it makes sense if you see a relatively inactive goldfish hanging at the bottom of your tank. And the reasons may or may not be related to health problems.

    Generally, if one spots goldfish at the bottom of the tank, it could be because the fish isn’t feeling too well. Either improper water conditions, lack of proper nutrition, stress, parasite, or bladder problems can all be reasons for your fish looking sad and isolated.

    It is best to visit your local vet if this behavior is prolonged.


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