How Do Fish Mate?

How Do Fish Mate
Photo by Worachat Sodsri

How do fish mate? This is a question many children, including adults, ask and, thankfully, have answers to. 

Sex and life are two related phenomena. In most cases, mating results in reproduction in all living things. Amazingly, this reality is the same for creatures that dwell underwater. 

Indeed, there are a million curious minds like yours. In this article, we’ll look at the reproductive life of fish and ultimately answer the question, ”How do fish mate?”

Fish Reproduction: Basics

Many activities occur under the sea, including male and female fish spending quality time together. So it shouldn’t be surprising that fish also mate and reproduce, with some laying up to hundreds of thousands of eggs. 

To know how do fish mate, here are some primary factors you need to know about fish reproduction:

Maturity age

Age and size are important factors when it comes to mating with different fish species. In other words, some fish species mate sooner than others. For instance, some fish species can mate a few weeks after hatching, while others might take years to become sexually mature enough to breed. 


The size of the fish determines the number of eggs laid, so the bigger the fish, the more eggs are produced compared to smaller fish. So this variable has to do with the quantity and size of eggs produced. 

How Do Fish Mate By Spawning?

Spawning is the release of eggs outside the body. Eggs and sperm released into the water are to produce offspring, and no physical touching is needed. Except for the aqua mammals and reptiles, most water animals reproduce by spawning. 

Some species of fish, big or small, that are monocarpic can only spawn once in a lifetime. Meanwhile, iteroparous species can reproduce multiple times during their lifetime.

After laying the eggs, the male simultaneously releases sperm to fertilize the eggs. This method is perfect for fish that have a short lifespan. At least they’ll be able to reproduce several times before they die or get eaten by bigger fish. 

Not all fish produce offspring by spawning, and some mammals, like sharks, make their babies by copulation. Additionally, even as virgins, sharks are the only mammals that reproduce without copulating. 

Reproduction Classification

The three major reproductive systems can be used to classify fish, including the ones below:

  • Oviparity
  • Ovoviviparous
  • Viviparous

Oviparity: Egg Layers

Oviparous fish produce their offspring by laying eggs. Examples of fish that use this breeding method are goldfish, tuna, eels, salmon, and many more. Ninety percent of bony fish are oviparous. 

After the eggs have been laid in the water, the male fertilizes them with his sperm. Afterward, the female lays as many eggs as possible, and this method is less stressful compared to carrying the embryo inside her body. 

The ability of a female to lay a particular number of eggs during the spawning season is called fecundity. Fecundity is the ability to produce large numbers of offspring, which is also determined by the size of the fish.

The ocean sunfish can produce around 300 million eggs in one spawning season. This is compared to the silver Arowana, which lays about 50 to 250 eggs in a spawning season.

However, that isn’t all there is to learn about how do fish mate. Egg layers fall into different categories:

Egg scatterer

Sticky or non-sticky eggs are laid in the water, and the male sprays its sperm on the eggs to fertilize them. Examples of fish that do this method are goldfish, cardinal tetras, zebra danios, and tiger bards.

Nest builders

The male builds the nest from a bubble nest or plant material, and the female then lays her eggs there. Afterward, the male fertilizes them with sperm. Siamese fighting fish (bettas), bluegills, and gouramis belong to this category. 


This class of fish is capable of protecting their offspring from predators. They keep their eggs in their mouths after they have been fertilized. This is a habit for Ariopsis Felis, cardinal fish, and blennies. 

Egg Depositors

Egg depositors such as dwarf cichlids and clownfish lay their eggs in one spot, and the male swims past and then fertilizes them. As a result, egg depositors lay fewer eggs compared to egg scatterers.

Egg Buriers

These species lay their eggs in the soil, and the male fertilizes them. The killifish is an example of a fish that practices this form of reproduction.


This class of fish reproduces differently. They lay eggs but preserve them in their bodies until ready to hatch. Interestingly, they do not feed off their parents. Instead, they develop with the egg yolk. 


These are livebearer species. The male inserts its sperm into the female. Sharks are the ideal example of viviparous animals. The offspring grows in her body, then draws nutrients to develop from her. 

Fish Gender Change: Is there a possibility?

Fish take gender-bending to a whole new level with their unique behaviors. For example, some species can have male and female reproductive organs, and they are called hermaphrodites even though most are gonochoristic.

They can change their sexuality after reaching a certain age and size. The process through which fish change from one gender to another is called protogyny.

Examples of hermaphrodites that have a protogynous pattern include parrotfish, wrasses, and many others. 

Fish can stay faithful: aquatic monogamy

After mating, the male sticks around to protect the eggs till they hatch. Some of the fish species bond immediately after the first mate. The bonding can be for a short period, then to just one breeding time, finally mating for a lifetime.

It’s a “till death do us part” for the four-eyed butterfly, also known as Chaetodo Capistrtus. 

Their species mate for life. Other species that also practice monogamy are mouthbrooders, substrate spawners, Cichlidae, and Osteoglossidae.


Knowing how do fish mate has significantly helped scientists monitor and understand the reproductive processes of countless sea dwellers. They’ve also been able to control the over-population and under-population of several fish species.

If you’re are curious about how do fish mate, then you’re in luck. Simply scroll up to get all the information you need.

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