How Do Fish Mate?

All living things reproduce; this is often an important part of survival for every species to confirm they do not become extinct. Freshwater and saltwater fish aren’t any exception.

There are two things the overwhelming majority of fish have in common:

1. They are vertebrates

2. They live in water

Apart from this, the remainder of their traits vary widely, including so many other ways of breeding and creating new life.

Well, How Do Fish Mate?

How do fish mate? In this article, we’re aiming to take a glance at the reproductive anatomy of fish, and other ways during which fish mate.

We’ll then dive into a number of the foremost popular breeds and discuss the way to create the proper conditions to permit you to breed them in your aquarium.

Reproductive Anatomy of Fish

All species of fish reproduce. Whilst reproduction isn’t needed for every individual fish to survive, it’s important for the species as a whole to survive.

Exactly how do fish mate/reproduce?

To understand how fish mate, it is very important to know their reproductive organs. For fish to breed, an egg and sperm should be combined to create a new beginning of life.

Whilst there are a couple of alternative ways in which this will occur, one general factor is the reproductive organs involved; the ovaries and also the testes.

The overwhelming majority of fish are dioecious (the sexes are separated), males have testes and females have ovaries. There are some breeds that contain both sets of organs (hermaphrodites); we will discuss this later.

Some species even have secondary organs called the genital papilla. It is a tiny fleshy tube found at the rear of the anus from which sperm is released.

Classifications of Reproduction

There are three major classifications of reproductive strategies which can be used to classify fish:

A. Oviparity

B. Ovoviviparity

C. Viviparity

Oviparous Fish (These are Egg Layers)

Similar to birds, reptiles, and insects, in oviparous fish, the embryo develops inside the egg, however outside of the parent’s body. Above 90 percent of bony fish are oviparous reproducers.

This method of breeding needs the female to lay eggs, after that the eggs will be fertilized by the male.

The majority of females can lay huge amounts of eggs just once because it takes very little energy to grow an embryo in an egg inside the female body.

The amount of eggs a female is in a position to produce in a spawning season is termed as ‘fecundity’. The fecundity of a fish is closely associated with the length and weight of the fish.

For example, the Mola (Ocean Sunfish) releases almost 300 million eggs during a spawning season whereas the Silver Arowana lays eggs just around 50-250 per season.

The egg fertilization will be done in a variety of different ways; either by the males rubbing their sexual organs on the eggs and releasing its sperm, or the male releasing sperm into the water to affix the eggs in the zooplankton layer (if the eggs are laid in that way).

Egg-layers fall under one of the following categories:

  • Mouthbrooders: Eggs are laid in the water and then collected in the mouth once fertilized. (Cardinalfish, Bettas, Blennies, Gobbies & freshwater Cichlids).
  • Nest Builders: Made from a bubble nest or plant materials, The male generally builds it. After that, the female fish stores her eggs there, and the eggs are fertilized by the males. (Gouramis, Bluegills, Bettas & Stickle-backs).
  • Egg Scatterers: Non-sticky eggs are laid by the female in open water. Generally, sticky eggs are laid in an undercovered area. After successfully completing the egg-laying process by the females, then the male fertilizes the eggs by swimming through that area. They spray semen in that area that is completely open or undercovered.
  • Egg Depositors: Here the eggs are laid in one spot, then the male swims past and fertilizes the eggs. (Dwarf Cichlids, Killifish, Clownfish & Rainbowfish).
  • Egg Buriers: In this situation, eggs are buried in the substrate, and then to fertilize the eggs the male dives into the substrate. (Killifish).

Viviparous and Ovoviviparous Fish (Livebearers)

In livebearers, fertilization and the development of the embryo occur inside the mother. The female is impregnated by the male’s changed anal fin, called the gonopodium. The sperm cell is discharged from the fin into the body of the female.

Ovoviviparous reproducers evolve their young inside an egg inside the mother’s body. However they don’t take any nutrition from their mother’s body, rather the egg’s yolk is used by them to develop.

In viviparous reproducers, the fertilization and development of the young co-jointly happen in the mother’s body. However, the embryos get nourishment from their mother.

Once the embryos are totally developed, then the mother offers birth to live young.

More Unusual Ways Fish Mate

Unisex Fish

There are some species of fish that reproduce by themselves. They are female fish, and so are the young they offer birth to.

It is debatable whether or not this could really be called ‘mating’ but it’s actually the way to breed.

The females could mate with males, however, the sperm isn’t used for reproduction.


Hermaphrodites have both male and female breeding organs. Generally, fish are born one sex and at a later age, they will convert to the opposite gender.

A female changed to a male is named a protogynous hermaphrodite. When a male switches to females is termed a protandrous hermaphrodites. Each of these sorts of reproducers still requires a fish of the opposite sex to breed.

A clownfish could be a nice example of a hermaphrodite. A bunch of clownfish can include one giant male, and one giant female, the remainder of the group are tiny males. Once the female leaves the group, her partner can be converted into a female and the next largest fish can become the new partner.

A small number of species constitute the classification of synchronous hermaphroditism, which suggests they will produce eggs and sperm cells at a similar time, for instance, the Mangrove Killifish.

When is a Fish Mature Enough to Reproduce?

Reproductive organs of a fish are typically the slowest organs to develop because they are not so important for survival at birth.

Different species reach sexual maturity at completely different ages; their readiness significantly depends on the size, species, and age of the fish. Generally the smaller the size of the adult fish, the earlier they’ll be ready to reproduce.

Some fish start to reproduce very soon after their own birth while others take years to achieve maturity before they are ready to reproduce.

How do Fish Mate and Reproduce (How Often)?

Depending on the species the reproductive cycle varies widely. Some fish reproduce several times the whole year (e.g. Guppies, Clownfish, Swordtails, Mollies, and Platys), others just reproduce throughout a specific season, and some only ever reproduce once in a lifetime and die when their egg or sperm is released (e.g. The Pacific Salmon).

Livebearers vs. Egg Layers

If you are simply starting out, we would like to suggest starting out with breeding livebearers. Typically they are easier to breed than egg-layers.

Species such as Platies and Guppies do not need a lot of facilities or specific conditions so they are an honest choice for beginner breeders.

Once you have some expertise with live-bearing fish, you will be able to move on to more hardy egg-laying fish such as Barbs and Danios.

The advantages of breeding livebearers instead of egg-layers are that the parents mate very easily without any problem and when their fry are born, they are much less needy.

How to Breed Fish in Your Aquarium

Choosing the Right Parent Fish

When you select your fish, you would like to make sure that you simply have a minimum of one male and one female fish (depending on the species the ratios vary).

Most fish are either sexually isomorphic or dimorphic:

  • Sexually isomorphic species have only a few variations if any at all, this is tougher to sex. Generally, the sole way to confirm the sex in sexually isomorphic species is by observing the shape of the genital papilla at the moment of spawning.
  • sexually dimorphic species will simply be distinguished by observing them. Their reproductive organs are formed differently, and their shape, size, and color are totally different. Males tend to be larger and a lot of vibrant than females

You can analyze each species to search out the variations to make sure you purchase the right sexes.

Other than confirming you select the correct sex, you would like to make sure the parent fish have decent colorings and markings and that they are mature and healthy.

It’s additionally important that they are compatible. In some species like certain cichlids, a pair can only form within a group after they have been raised along. If some species are simply thrown together, one could bully the opposite to death.

If you are selecting a species that does not reproduce easily, keep an eye out for those showing courting behavior.

Once you have selected an appropriate pair (or group if they’re shoaling fish) they must be conditioned. Conditioning means that to feed your fish different types of foods to make sure they’re in the best shape possible before they reproduce or breed.

If you get your fish in early spring/late winter, they will probably already have been conditioned and they’ll be ready to breed.

Setting The Right Tank Conditions

It’s important to know the breeding environment,tank conditions, size, and spawning behaviors of every species if you would like to get success in breeding. Some species need a separate tank or bare tanks for breeding and raising the fry, while other species need some plants and water flow.

Bring the water pH and hardness to the specified levels (specific to each of the species) and additionally, increase the aquarium water temperature by about 10F above its normal temperature.

Separate the male and female fish with a transparent glass partition. This will increase the desire to breed when they are given the chance to mate.

We will look at some popular breeds below and also each of their requirements. If your breed is not mentioned and listed below, you have to research the fish tank conditions and environment required before starting to breed the fish.

How Popular Breeds Mate In Fish Tank (+ Best Optimal Tank Conditions)

Now we are going to take a view at two very popular species that people would like to breed; Goldfish andBettas.

We will not go into detail about how to breed other popular live-bearing fish (such as Platies and Guppies) because they are very straightforward to reproduce and they really do not require stringent tank conditions.

Betta Fish Breeding

Fish Tank Conditions

How do fish mate in an aquarium? Well, it is very important to get the tank conditions correct before trying any mating. You will require a sponge filter, newly hatched brine shrimp and floating plants, or some other adequate food to feed the fry.

It goes without saying anything that any fish tank you are putting fish into must be cycled.

The water in the aquarium is to be heated up to around 82oF (28oC). Make sure the remaining of your water parameters are reading properly before you try to breed.

If you are using any particular breeding tank, it must be between 5 and 10 gallons. To separate the male and female before you put them together, place a removable divider in the center of the fish tank.

Leave the bottom of the fish tank bare – if eggs fall they shall get lost in the substrate at the bottom of the aquarium.

Mating Ritual

Male Bettas achieve their sexual maturity at around 3 ½ months from their birth. An indication that they are able to begin mating is when they start to establish bubble nests. Upright bar markings are developed by the females on the side of their bodies which indicates they have achieved sexual maturity too.

Once the male Betta has designed a bubble nest remove the glass divider (it may take anywhere from a few hours to a couple of days).

When they are placed together for the first time, you will notice them fighting. This can be normal, and a part of the mating practice, however, keep an eye on them to make ensure neither is injured.

If a male is interested in a female partner he will widen his gills, twist his body, and spread his fins. If a female is interested she is going to curve her body back and forth and switch a darker color.

When the female is prepared to mate, she is going to spend plenty of her time close to the bubble nest.

The male shall circle her and take his time in choosing the most effective positioning. Both of them will then embrace (it is known as the nuptial embrace) for a few moments, and then the female will start to release eggs. When they embrace each time the female can release between 10 to 40 eggs. The process of embracing will continue until the female has no eggs left.

As soon as the female has released all her eggs, she should be removed from the tank – else she will usually eat the eggs.

Once the female has been removed from the tank, the eggs will be fertilized by the male by releasing milt into the fish tank. The male will gather them and place the eggs in the bubble nest and they will continue to take care of the eggs for the next 24 to 36 hours, continuing to pick the eggs to the bubble if they fall.

The male fish is generally removed from the fish tank once the fry has emerged.

Goldfish Breeding

Fish Tank Conditions

Again, you have to make sure your tank is totally cycled and stable, and big enough to accommodate an adult goldfish.

The fish tank must be well planted. It should be kept at around 64OF for about four months.

After that, the aquarium should slowly be re-warmed to 70-74OF for more than a two-week time period. It will then mimic the mating season which they are used to in the wild and will initiate breeding.

Mating Ritual

You should have a minimum of one 3-year-old male and female in your aquarium. The younger females will reproduce, but they may become egg-bound which is dangerous for them.

Signs that the goldfish are able to mate include white spots along the gills of the males and the female will become more rounded and fatter.

To encourage the female to release her eggs the male will chase the female around the tank. This ritual is extraordinarily powerful and when the female becomes very tired she cannot continue, then she will release the eggs. The females will release up to 10,000 eggs.

The eggs will stick with the plants and also the wall of your fish tank, and at that time the male will release his milt to fertilize the eggs released by the females. This process will make the water cloudy – but that is usual.

The fertilized eggs are clear, and unfertilized eggs become white. Remove the unfertilized eggs from the tank as they generally develop fungus that can pollute your tank water.

Then you may shift the fertilized eggs into a new fish tank so that the adults do not eat them.

5 Facts You Didn’t Know About Fish Mating

  1. Female fish areattracted to those males who flirt with other males.
  2. The annual Sardine Run in South Africa produces a lot of sperm and eggs that it’svisible from the air.
  3. Many Killifish release eggs that survive even when the puddle they live in dries up, and after that hatch again when it rains.
  4. To deposit its eggs on an overhanging leaf the Splashing Tetra jumps out of the water, it will then splash the deposited eggs to keep them wet, and they will fall back in as they hatch.
  5. Freshwater Gars produce eggs that are so poisonous if eaten!


How Do Fishes Get Pregnant? There are different ways in which fish mate and reproduce.

Some fish keep it quite plain, easy, and simple like us humans. The male inseminates the females who then grow the fish inside the female body whilst nourishing it. While others release eggs that are fertilized by the male.

There are so many species of aquarium fish that are relatively simple to breed so if you are just a beginner, we suggest you start with one of the easier breeds listed above.

Your tank conditions and mating rituals so much depend on the particular species. So if you’re a more advanced fish keeper and want to breed more difficult breeds, always research the conditions they want.

Did you know there are plenty of ways in which a fish can mate? Do you have experience in breeding any uncommon fish? Have you got any value from this article “How Do Fish Mate? How Do Fish Get Pregnant [501 Top Secret]”… We would love to hear from you; let us know in the comments section below…


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.