How To Tell If A Goldfish Is Male Or Female?

Goldfish are one of the most common and easiest to care for pets that can come in various colors and patterns. What happens when it comes time to name your new friend, and you don’t know if they’re male or female? Or if you want to start a little goldfish family, but you need to make sure you actually have a potential breeding pair?

In this article, we’ll provide you with a few different methods of determining the sex of your goldfish based on various physical attributes and behaviors. We’ll also inform you of other interesting facts about your goldfish, such as the proper age to determine sex and if goldfish can change sex.

How Can I Tell If My Goldfish Is Male Or Female?

There are several ways to tell the sex of your goldfish through the observation of physical characteristics. We’ve listed these characteristics below to help you determine if you have Sally versus a Harry.

Breeding Tubercles

When males are ready to start making babies of their own, they develop breeding tubercles or breeding stars that resemble white pimples on their pectoral fins and gill coverings. These tubercles are usually rough to the touch, and it is speculated that they may be used during courtship or to fight off other competing males.

Females do not develop these breeding stars, so it is most likely a male if your fish displays these pimple-like spots. However, be careful not to confuse them with ich or white spot disease, which can infect either gender and usually displays a random pattern all over the body.

Body Shape

While body shape is not the most reliable method of determining sex, it can help. Females tend to be rounder and shorter. Their roundness is especially prominent during the breeding season as their abdomens are filled with eggs. Take care not to confuse gravidity with infection or simple fatness from overeating, though.

A male’s body shape is typically longer and thinner than the female’s. This method is a good confirmation technique, especially if you have more than one goldfish to compare, but it should not be used as the primary sexing method. 

Vent Shape

The shape of the waste disposal opening underneath the anal fin is another way to tell if you have a male or female goldfish. Males tend to have a thin slit that is concave, while females sport a round, convex opening.

However, it can be very tricky to determine this, considering how small it can be and the natural tendency for your fish to move around, preventing you from getting a good look.

Pectoral Fin Appearance

Male and female goldfish have front fins with different shapes and lengths, which can be an excellent way to determine their gender. Male goldfish tend to have thinner pectoral fins that are long and pointed. On the other hand, female goldfish sport shorter pectoral fins with thicker fin rays than males.

Ventral Ridge

Another method of determining the sex of your goldfish is to look for a ridge on the underside of the body. Males tend to have a ridge that runs down the length of the body but is especially pronounced from the pelvic fins to the anal opening. Females may have a smaller, less obvious version of this ridge but most likely will not have one at all.

Due to this ridge, a male’s abdomen tends to be more rigid, while a female’s abdomen is softer and more flexible to allow for growth when she is bearing eggs.

Goldfish, aquarium, a fish on the background of aquatic plants

How Old Does My Goldfish Need To Be Tell If They Are Male Or Female?

Goldfish need to be sexually mature in order to determine if they are male or female. Most goldfish reach sexual maturity around one year of age, although some can peak earlier at around nine months old.

Most of the physical and behavioral characteristics used to determine the sex of a goldfish will not be developed before the age of one, so it can be virtually impossible to determine your goldfish’s gender before then. The best time to determine whether your goldfish is a male or a female will occur during the first breeding season after your goldfish has reached sexual maturity.

Other Characteristics Of Male vs Female Goldfish


One of the most obvious behavioral methods of determining your goldfish’s sex is observing what is released when spawning. Females will drop a lot of orange-colored eggs as they swim through the tanks, while males will milt what looks like cloudy white sperm.

Breeding Behavior

Female and male goldfish behave differently during the breeding season. While females are more active outside of the spawning period than males, the opposite is true when it’s time to make babies.

Males often display chasing behavior or actively nudge females, while females tend to either be fairly inactive or hide to avoid overenthusiastic males.


Male goldfish tend to be aggressive when it comes to breeding season, while females prefer to be left alone. If your goldfish is picking a fight with another fish or insistently nagging, it is probably a male. Females will not engage in fighting behavior and rather tend to hide if overly bothered.

Raggedy Appearance

While not the best indication of sex determination, if you notice that your goldfish’s fins are becoming tattered and torn during the breeding season, it is most likely a female. Males can tend to be aggressive in their pursuit of females. As such, males will nip at females’ fins or push them into plants causing the female’s fin to rip and tear.

Males usually do not look as raggedy because fin nipping is not typical in male-to-male combat when they display aggression towards each other.


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Do Male Goldfish Become Female?

While sex change is common in other species of fish, goldfish can not change their gender from either male to female or female to male. Their gender is fixed at birth and is fully revealed upon sexual maturity and the advent of their first breeding season.


Goldfish are wonderful pets whose fun and animated antics can light up a room. Before you get down to the tricky task of choosing a name for your new aquatic amigo, there are a few things you need to know in order to determine whether you’ve got a male or female goldfish.

First, they need to be old enough to determine sex – at least twelve months old. The best time to determine sex is going to be during their first breeding season after they reach sexual maturity at the age of one.

There are several physical characteristics to help you figure out if you have a male or female goldfish, including the presence of breeding tubercles, pectoral fin and body shape and length, anal vent opening, and ventral ridge. In addition, behaviors such as chasing, fighting, and nipping can aid in sex determination.

Whatever the gender of your goldfish, take heart that once you’ve settled on the perfect male or female name that you won’t have to change because your goldfish is a he or she for life.

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