How Do Fish Mate? Can they Crossbreed?

how do fish mate

Like all living things, fish reproduce too so that they don’t become extinct. Mating is essential for the survival of each species. 

For fish, every species has different traits, and they follow different mating and reproducing methods. But have you ever wondered that how do fish mate?

In this article, first, we will look at fish reproductive anatomy and how fish mate. And if you are a new fish breeder, then you will find the answer to questions like which is the easiest fish to breed and how to create an ideal breeding condition in your fish tank.

Basics of Fish Reproduction

You need to understand some crucial parameters to comprehend fish reproduction better. 

1. Sexual Maturity

Different species of fish have different ages of maturity to be able to reproduce. Maturity age is typically calculated in females. Fish that reaches sexual maturity remain that way. There isn’t much evidence that fish experience sexual senescence or grow too old to breed.

2. Fecundity

It means an individual’s maximum possible reproductive output: the number and size of eggs produced. Fish length, weight, and ovarian weight are closely related to the fecundity of a fish. Bigger fish lay disproportionately more offspring and larger offspring than smaller fish.

3. Spawning Frequency 

Most fish spawn to reproduce. During “spawning,” fish release gametes from the body into the surrounding, which causes fertilization.

Small forage fish and even bigger fish like salmon, which are semelparous, can only spawn to reproduce once in their lifetime. Fish of the iteroparous family can repeatedly spawn over their lifetime.

4. Mating Season

It depends on the species when fish mate.

Some fish can breed every season throughout the year. In contrast, there are some species that can only reproduce during a specific season. For them, the right water temperature and getting an abundance of food are necessary to breed. 

Fish Reproductive Anatomy

Understanding the fish’s reproductive system is very important before looking at the various methods by that fish mate.

For fish to reproduce, similar to most vertebrates, an egg and sperm must come together. While reproduction can happen in many ways, the common factors in every method are the testes and ovaries, the fish’s reproductive organs.

Since most fish are dioecious, which implies sexes are separate, females have ovaries, and males have testes.

Some fish species are called hermaphrodites. Here, the individuals have both sets of reproductive organs. Then, several types of fish have secondary reproductive organs: small fleshy tubes named genital papilla. These are located at the back of the anal fin, and from here, fish release their sperm.

How Do Fish Mate: 3 Methods of Reproduction

The 3 most used methods of reproduction by fish are-

  1. Oviparity
  2. Ovoviviparity
  3. Viviparity

Oviparous Fish

In oviparous fish, the embryo grows inside the egg but outside of the fish body. 

More than 90 percent of fish are oviparous breeders. In this reproduction method, female fish lay eggs, and male fish fertilize the eggs.

Male fish fertilize the eggs in two ways-

  • They discharge their sperm directly onto the eggs
  • They release the sperm into the water that reaches the eggs in the zooplankton layer

Oviparous or egg-layers fish are classified into one of the following groups:

1. Mouthbrooders

Here the female fish lay their eggs in the water, and then the male fish fertilize them. Once fertilized, parents collect the eggs and hold them in their mouths until they hatch.

mouthbrooding jaw fish is holding egg in its mouth
Image credit: SergeUWPhoto, Shutterstock


Though male and female fish contribute equally to raising the family in some species, interestingly, male fish often perform mouth-brooding duties.

Bettas, Blennies, Cardinal fish, freshwater Cichlids, and Gobbies belong to the mouthbrooders group.

2. Egg Scatterers

Egg scatterers lay their sticky eggs in undercover areas and non-sticky eggs in open water. The male fish swims through the carpet of eggs and deposits semen to fertilize the eggs.

Examples of some egg scatterer fish are Cardinal Tetras, Goldfish, Koi, Tiger Bards, and Zebra Danios.

3. Egg Buriers

Egg buriers like Killifish lay their eggs on a substrate to hide them. The males then dive into the substrate and fertilize the eggs.

4. Egg Depositors

Female fish deposits her eggs in one spot. The male fish swims over those eggs to fertilize them.

Clownfish, Dwarf Cichlids, and Rainbowfish are known as egg depositors.

5. Nest Builders

These species build a nest to protect their eggs from predators until they hatch. Generally, the male fish build the nest, and if the female fish is satisfied with the male’s handiwork, she releases her eggs in the nest, where the male fertilizes them by dousing them in sperm.

Males build the nests using bubbles, plants, and substrate. This type of fish list includes Bettas, Bluegills, Gouramis, and Stickle-backs.

You may also like: A Care Guide for Sucker Fish

Ovoviviparous and Viviparous Fish

Fish that use ovoviviparity and viviparity reproduction methods are commonly known as livebearers.

Livebearers are the best choice if you want to start breeding fish in your fish tank.

In livebearers, egg fertilization and embryo development occur inside the mother. The mother carries the eggs, and the father deposits his sperm into her body using his modified anal fin called a gonopodium.

Ovoviviparous reproducers grow the baby inside the egg and the mother’s body. But the mother doesn’t provide them with any nutrition. Rather the youngsters feed themselves their egg’s yolk sac to grow.

In viviparous reproduction, eggs are kept, fertilized, and developed inside the mother’s body, similar to ovoviviparous reproducers. But here, the mother provides the embryos with nourishments. 

It takes two to four weeks for the embryos to develop fully. And once they are fully developed, the mother then gives birth to fully-formed live fry. Guppies and platys are two examples of livebearing species.

Unusual Fish Mating Methods

Synchronous Hermaphrodites

Some species can simultaneously generate sperm and eggs as they have both male and female reproductive organs in their bodies. These fish are female, and so are the offspring they produce. 

While it’s debatable if this can truly be described as “mating,” there is no doubt that this is a reproduction method. 

Sequential Hermaphrodites

Some hermaphrodites undergo a weird change called “sequential hermaphroditism.” These species are born of one sex, but as they mature, they can switch to the opposite sex.

The process of a female, hermaphroditic fish becoming a male is called “protogyny,” and  the process of a male fish becoming female is known as “protandry.”

colorful clownfish flowing underwater
Image credit: Alex Stemmers, Shutterstock

However, sequential hermaphrodites still require a fish of the opposite sex to breed. A clownfish is a great example of sequential hermaphrodites.

How to Breed a Fish in a Fish Tank?

Step 1: Select a healthy mature for each sex of the species you want to breed. Sometimes, you may need more than one male or female for breeding.

Step 2: Place the couple together in a separate breeding tank.

Step 3: Provide them with enough nutrient-rich food to increase their fertility.

Step 4: Do enough research on the mating habits of the fish you’re attempting to breed.

Step 5: Create a perfect condition in the tank so that they can mate. Such as ensuring the right tank size and clean water, and the right temperature.

Step 6: Create an ideal physical environment in which the parent fish prefer to mate. For example, add plants, stones, and artificial tunnel structures to the tank to replicate the natural conditions.

Step 7: Once the mother lays the eggs or gives live birth, bring both parents back to their original tank.

Step 8: Cover the tank on three sides to protect the eggs or newly hatched fish from the outside light. This is a crucial step because eggs and newly hatched fish can be sensitive to light. You can cover it with paper or thick fabric.

Step 9: Change the tank water daily because to learn to breathe and filter, the fry needs clean water.

Step 10: Once the egg sac of the fry disappears, start feeding them.

Fish That Breed Easily

Do you have a thing for the fish world and want to become a fish breeder? Livebearers fish are the best choice if you want to start breeding fish in your fish tank.

Here are the names of fish that are easy to breed.

1. Zebra Danios

Zebra Danios are gorgeous, easy-to-breed fish. They are perfect for novice breeders.

To breed, put two mature males and one mature female together in a breeding tank. The breeding tank should be about 10 gallons, and the temperature should be around 71° Fahrenheit.

Once parents lay and spawn the eggs, remove them from the breeding tank to stop them from eating the eggs and frying.

2. Guppies

Guppies are famous for being the easiest fish to breed. All you need to do is put a matured couple together in a separate and right-sized tank to breed, and they will do the job. Also, remember to keep the tank clean and maintain the water temperature. 

Did you know that a female guppy can reuse the sperm to fertilize the eggs for about 8 months? So, a female Guppy will continue to reproduce young guppies even if her partner dies.

3. Mollies

Similar to Guppies, Mollies are great breeders too. But they require a lot of additional care. 

You need to create a perfect condition—a clean tank and the right water temperature—in the tank for breeding. Otherwise, Mollies won’t breed.

Because male Mollies breed enthusiastically, you should keep multiple females (at least 3) for one male to lessen the pressure on one female for breeding.

And once Mollies give birth to the babies, put them in a separate tank as Mollies tend to eat their own young.

4. Anableps 

If you are looking for big fish to breed, go for Anableps. However, because they only have organs on one side of their bodies—either the left or the right—right-sided females can only mate with left-sided males.

So,  put sufficient numbers of males and females in the tank and ensure they are physically compatible.

5. Platys

Platys are also easy to breed. However, Platys are known to eat their own young as soon as they hatch. So, move the fry to a separate tank once they are born.

Also, compared to species, male Platys can be a little aggressive. So, keeping at least three females for one male is better. That way, females will be a bit less stressed. 

6. Convict Cichlids

They are another easy breeder. Convict Cichlids are overprotective of their fry and won’t eat their fry. So you can easily let them raise their fry in a separate tank.

7. Mosquitofish 

Mosquitofish are a simple species to breed, and they can easily reproduce under normal conditions. It takes the female Mosquitofish two months to start breeding.

8. Rosy Barb

Rosy Barb can easily mate and breed. Simply feed them enough nutrient-rich food and keep the tank water always clean.

Put a nice breeding pair in a tank with lots of hiding places. Once they lay the eggs, the parents are in a different tank.

Because  Rosy barb’s eggs typically hatch within one to two days and these cute little fish have the habit of eating their little ones, separate the fry and parent quickly.

9. Swordtails

Swordtail fish are attractive livebearers who breed actively without any major intervention from the owner. 

You just need to put at least three mature females and one mature male in the same tank for less stressful breeding. A female Swordtail can breed every 28 days.

Once the babies are born, separating them from their parents is better to keep them alive. And if you want to keep them together, then at the very least, stock the tank with lots of vegetation where the fry can hide.

10. Killifish

Breeding a Killifish is easy, but you will need to be patient. Annual Killifish species bury their eggs in the sand, and the eggs hatch in about 1 to 4 months. It’s a bit easier to breed the non-annual Killifish.

What Do Fish Eggs Look Like in a Tank?

Regardless of how vibrant your fish looks, its eggs will probably resemble white or translucent poppy seeds that are less than 1 mm in size. The eggs are sticky and adhere to a decor, substrate, and plants.

After the male fertilizes them, the eggs take on a yellowish or orange hue.

Can Fish Crossbreed?

In general, species that are closely related can crossbreed, which is known as a hybrid.

However, according to new research, fish will mate with species other than their own if the male’s coloring is alluring enough or if the female can’t see him clearly. Such mating choices can result in the evolution of new species.


Fish mate and reproduce using various methods.

Some keep it as straightforward and easy as humans do, where the male fertilizes the female, who then nurtures and raises the fish inside her body. Others deposit eggs, which the male then fertilizes.

And there are fish species that are easy to breed in an aquarium. So, if you are a novice breeder, you can start with any of the fish listed above.

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