How to tell if a fish is male or female – Fish Camp Rehab

How to tell if a fish is male or female? This is a question that is frequently asked and the quick response is yes.

A majority of aquarium fish, including goldfish, koi, or betta fish are female or male. Their sex can be determined. The gender of the fish isn’t a factor unless you’re considering fish breeding, and that could be a challenge.

How to Determine the Sex of Your Fish

To establish if the fish is female or male, it is necessary to be patient until your fish reaches maturity and then examine the body’s characteristics and behavior. It is extremely difficult to identify the gender of a fish prior to that point.Certain species, like angelfish and betta fish exhibit distinct colors between females and males.

Based on the species of fish, the process of determining the sex of a species of fish is simple to almost impossible.

Understanding the differences in the sexuality of aquarium fish is crucial in breeding fish and for selecting the appropriate proportion of fish to an aquarium that is a community.

Although not all fish species can be identified with sexual activity, these suggestions will assist you in identifying the sex patterns of most of the species of fish in aquariums.

Do fish have genders?

Determining fish gender:

Since sex organs aren’t vital for survival, they are developed only in fish that are unique. Without a complicated DNA test, you’ll have to wait until the fish has become an adult, which is usually at least one year.

When the animal is dimorphic in sexuality you’ll be able to observe any gender differences on the outside. For example, taking a look at thefins that are on the undersideof the fish can be a popular method to determine the gender of a fish however, all species are somewhat different.

The fin beneath the fish just behind the belly, commonly known as the anal fin is the place where the majority of varieties of fish have reproduction organs. Typically, the male anal fins are bigger or longer than females.

Guppies, goldfish, and koi fish are some species that use this method. helpful in distinguishing the males and females. However, sexually isomorphic fish like cichlids display gender-specific signs only when they are breeding, which makes them less likely to be sexable.

Female fish have specific characteristics.

In the majority of fish species, females tend to be larger than males, but they do not necessarily have a longer. This is especially true of species like goldfish or Koi fish during mating season.

The females are bursting with eggs and are visibly larger than males. Many fish species reproduce when females release eggs while the male swims around the eggs and fertilizes them.

The most common method to establish the gender of a fish is to look at the behavior of fish during the mating season. Female fish are slow and less mobile.

On the other hand, males are typically more active, sometimes even pushing the female around to encourage the release of eggs. Koi and goldfish are examples of species that display this behavior.

The characteristics of male fish

In certain species of fish, males are evidentby their traitswhich can be observed with no close scrutiny. For instance, if the fish has a huge bump, called a nuchal-hump on its forehead, it’s a male.

The male Oscars and angelfish also have a nuchal hump. Male fish also typically are larger in their dorsal fins which are the fins that lie on side of the fishes do females. In other species like betta fish, males sport more visible and vibrant fins than females with muted colors. counterparts.

During mating season, males of certain species of fish like goldfish develop white bumps around the fins, gills, or head.

The bumps could draw female attention, but they will disappear following mating season. In the same way, male pleco fish (a kind of sucker) grow long whiskers in their mouths and pectoral fins during the mating season.

There are hermaphrodite fish species.

Most fish species are born gender-neutral or male. There are a few rare species that are gender-neutral.

Many aquarium fish species have genders however,this species is a unique species. Clownfish (best well-known for its role in Nemo in the Disney film) is able to change genders.

A group of clownfish can consist of one male who is massive with a large female as well as a number of smaller males. If females leave this group largest male will change to the female form, and a different male will take his place as the biggest male, and they will mat.

Common Pet Species: How to tell if a fish is male or female

Here’s how you can identify the sex of fish that are commonly found in aquariums. This isn’t an exhaustive list however it will give you a description of the distinctions between the sexes of fish.


Angelfish are very difficult to determine precisely to determine which gender is which especially when they are young one. Some fully mature males display a slight nuchal hump. This is an oblique bump on the forehead close to the eyes. Do not expect it to be always present, however.

The most effective method to establish the possibility of mating is to buy a few immature angelfish and keep them together. When they’re mature enough, they’ll start pairing off, and you’ll have at minimum one breeding pair within the ensemble.

When they start mating, it’s very clear which male is the other female, since she is the one with the ovipositor that is responsible for laying eggs. The ovipositor is a small tube that is located in the female’s vent which she is using to lay her eggs.

It has a rounded end. Males use an elongated tube that extends out from their vent to fertilize eggs after they have been laying by the female. Both parents take turns hovering over the eggs and blowing them out with fins to help them breathe and ensure they are clean.


Female goldfish typically are fatty, with round bellies that are full of eggs. Male goldfish have two distinct physical features (roughened pectoral fins) bumps that are raised around their operculum. This is the most frequent feature in comet goldfish. However, not all goldfish, particularly extravagant varieties, show sex differences.


Bettas are a kind of fish that is easy to distinguish their sexes. Males sport long flowing fins , and stunning colors that many owners consider attractive. Male bettas are that are usually offered in stores.

Females aren’t as vividly colored and come with shorter fins and stubbier ones, however, certain male betta species may also have fins that are shorter.

It can be difficult to locate female bettas that are available in pet fish shops If you are unable to locate one and you are unable to find one, ask the store manager or owner to order the animal for you.

Male bettas need to be kept away from each female until the time she is in the right place to breed. The male constructs the nest of air bubbles that are floating on the water.

He then lures her to put eggs inside it. He wraps him in her body in order to fertilize the eggs while she lay eggs. Then, he takes the eggs with his mouth before placing the eggs in his bubble nest.

After the breeding process is complete the male chases the female away and takes care of the eggs and babies.2 Females must be removed, or else she’ll be slain by the male.


Many people believe that the goldfish’s characteristics will be evident in koi. However, this is not true. Males are generally smaller and skinnier on their bodies.

Females are larger and more round. In the spawning season females’ vent will be swelling and puffy, as compared to the male’s vent which is tucked in. But, some of these external visual clues may be misinterpreted!

Fish whom we’ve believed to be the same sex were proven to be different through ultrasound. Our office uses ultrasound to determine sex, however, we are unable to determine reproductively-immature individuals or stressed individuals who have sacrificed their reproductive capabilities.


In general, the sexes of catfish are not easily separated. A variety of catfish species haven’t been bred in the wild. The only exception to this can be the Corydoras species which is often bred in captivity.

For the Corydoras, catfish females are typically larger-bodied in comparison to males. Males will chase a female with a gravid (full with eggs) around the tank, and after that, she will lay the eggs floating on the surface like a leaf of a plant or smooth rock or even the glass aquarium. The males swim across eggs and fertilize the eggs. After that, the eggs are taken away.


Cichlids are such an incredibly diverse group that it would require an entire novel to provide specifics on the differences between species. Although many species aren’t easy to distinguish, however, there are some guidelines that can be applied to a variety of species of cichlid.

Males tend to be slimmer, but are also larger-bodied than females. They have more vividly colored. The anal and dorsal fins of males are larger, more pointed, and flowing than those of females. In some species, males have egg-shaped marks in the fin’s anal that is referred to as eggs spots.

Males may have an ear bump called the nuchal hump. While females also can develop nuchal humps when they spawn it’s not more prominent than that of the male. The dominant male will typically have a bigger nuchal hump than the other males.

While the general rules above apply to all species of cichlids you’re thinking of breeding them, make sure you do research on the particular species before you look for the perfect breeding pair.3


Barbs, as well as other members of the Cyprinid family, are difficult to distinguish between.

The differences will differ by kind, however, generally speaking, males have more vivid colors and are thinner than females. Because the majority of cyprinids school fish, one method to acquire a breeding couple is to buy an entire group of them.

Certain species of cyprinids such as goldfish, males develop tiny black bumps (nuptial tubercles) on their heads the operculum, and the pectoral fins, during the season of mating.

Males chase the female, who will lay eggs, and the males fertilize them while they deposit eggs. After the breeding process, typically there is no concern about the eggs and parents could even take them in if they’re discovered.


Gouramis are different species of fish that is not readily identifiable. Females and males are typically similar in appearance and color. However, there is an unavoidable sexual difference found in the majority of gourami species. The dorsal fin is lengthy and reaches the point of no return for males, whereas females are shorter and have a round dorsal fin.

Furthermore, certain species of gourami display gender-specific color differences. Male gourami with pearls displays a deep red-orange hue on the breast and throat. The male moonlight gourami is a color of red to orange on those pelvic fins. Much like the betta gouramis build a bubble nest, but both males and females take part in caring for the eggs.

Livebearing Fish

One of the easiest fish to distinguish is livebearing fish like the guppies platys, mollies, and swordtails. Males tend to be smaller and brighter than females. They also have an external organ for sexual reproduction, the gonopodium. This organ allows them to distinguish between males and females.

For males, the anterior fin is rod-shaped while females have an oblong-shaped, traditional fan-shaped fin. The gonopodium can be used to fertilize eggs within female fish. The male fish swims with the female. The fertilized eggs inside will be born inside the female and they can “give birth” to the baby fish.


Live-bearing fish could be a major problem when you are unable to distinguish between males and females! The gestation time is about a month, one pregnant mom can easily turn into an entire school!

The majority of female guppies are bigger with bellies that are larger However, the most reliable method of determining this is looking at the anterior fin. It is the fin that lies beneath the fish, right in front of their anus. Males have large pointed anal fins and females will have a triangular, shorter anal fin. Don’t rely on color to discern the difference!


Tetras can have some distinctions between males and females. They differ based on the specific species. Females tend to be bigger and plumper than males.Males tetras are typically more vibrantly colored and have larger fins than females.

Tetras are schooling fish therefore pairings of breeding can be acquired just by purchasing a tiny collection of them at a time. They generally breed through males who chase females and fertilize eggs as they are laid in plants or scattered on the rocks. There is no supervision for the eggs that could be eaten by fish.

That’s just a sample of some of the more popular species of fish for pets.Here’s a useful source for information on the various species of fish.

All fish species come with their own method to distinguish males and females apart, however, when you’re not an animal, you may not be able to recognize the differences! If you’re keen on breeding the fish you have, suggest getting in touch with a professional breeder for some suggestions.


Dibyajyoti Bordoloi is the creator and author of, a third-generation experienced fish keeper and owner of a successful pet breeding farm. He is also a member of the Center for Wildlife Rehabilitation And Conservation (Assam), the Marine Aquarium Societies of North East India, and the Kaziranga Nature Conservancy of Assam.

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