You are reading this post because your parents mated and reproduced.

Every living organism on earth reproduces, this is how species stay away from extinction.

In this post, I will talk about how fish reproduce in an aquarium.

Most fish reproduce sexually, requiring a male and female. Fish species are extremely diverse, some species such as the Amazon molly is an all-female fish that doesn’t require a male to reproduce.

Firstly we’ll talk about the details of how fish reproduce, then we’ll talk about how you can use this information to breed fish in your aquarium.


For fish to reproduce, a sperm & egg must be combined together. (Ovaries and testes)

Just like humans, female fish have ovaries and males have testes. Some species are hermaphrodites, meaning they have both male and female sexual organs.

Some species also have secondary organs known as “genital papilla”, a fleshy tube that releases sperm.

Three types of reproductive strategies:

  • Oviparity
  • Ovoviviparity
  • Viviparity

Quite a tongue twister, I know

Oviparous – Oviparous fish.

Just like snakes, birds and insects, oviparous fish lay eggs. The embryo develops outside of the parent’s body, inside the egg. Around 90% of bony fish reproduce through oviparous mechanisms.

Because the embryo grows outside of the fish’s body, female fish can lay huge amounts of eggs at once. For example, the ocean sunfish can release 300 million  eggs in a single season, whereas the Silver Arowana lays around 150 eggs per season.

Eggs must be fertilized by a male fish, fertilization of eggs can happen in several ways – rubbing sexual organs on eggs, releasing sperm onto eggs, releasing sperm into water, joining sperm to the zooplankton layer of the eggs.

There are several types of egg laying fish:

Buriers: eggs buried in the substrate

Depositors: Eggs are laid together, the male fish will swim past and fertilize them.

Scatterers: If sticky, the are laied under cover. If not sticky, the eggs are laid openly in the water. The male fish will swim past the group of eggs and spray semen in the water around the area, if the sperm reaches the eggs successfully, they are fertilized.

Nest builders: Fish nests can be made from plant materials or a bubble nest. This is usually built by the male, the female lays her eggs inside the house and the male fertilizes them. One of the most famous fish (betta fish) does this.

Mouthbrooders: Eggs are first laid in water, after fertilization, they are safely stored in the mouth.

Ovoviviparous and viviparous fish (livebears)

This is similar to how humans give birth. The fertilization and development of the embryo takes place inside the mother.

The male impregnates the female via a modified anal fin (gonopodium). The male’s sperm is released into the female’s body from the fin.

Ovoviviparous reproducers’ young develops inside the mother’s body. The mother’s body does not provide any nutrients to the embryo, it feeds off the yolk inside the egg.

In viviparous reproducers, fertilization and development of the embryo also occurs inside the mother’s body but the embryos do receive nutrients from the mother in this case.

Once an embryo is fully developed, the mother gives birth to living young.



Some species of fish can reproduce by themselves. These fish are known as hermaphrodites and contain reproductive organs of both genders. Usually, fish are born with one gender and switch to the other gender as they grow older.

A protogynous hermaphrodite is when a female switches to a male whereas a protandrous hermaphrodite is when a male switches to a female, the next largest fish will become the new partner.

A small amount of species fall into the category of synchronous hermaphroditism, meaning that they can produce eggs and sperm at the same time – eg, the mangrove killifish. 


The frequency of fish reproduction varies widely between species.

The most (multiple times a year) include guppies, mollies, clownfish, platys.

Some, such as the pacific salmon, only reproduce when they die and their sperm and egg is released.


The reproductive organs of a fish (just like humans) are the slowest to develop because they not not essential for survival at birth.

Just like reproduction frequency, the age of reproduction varies widely between different fish species.

Size can be used as a general indicator to the age of which a fish can start to reproduce. Generally speaking, the smaller the fish, the earlier it can start to reproduce. Some fish take days, some fish take years.


Livebearers are much easier than egg-layers.

Their parents mate much more easily without the need for much help, their young are also much less nedey than egg layer species.

If you’re just starting out its much easier to go with livebearers because they require much less help, making them suitable for beginners.

If you’d like to raise some egg laying fish in your aquarium you can go for species such as Barbs and Danios, their eggs tend to be tough and hard to kill.



Selecting the right fish to be parents is extremely important. When selecting the right fish, make sure you have a 1:1 ratio of male:females.

How do you identify the gender of a fish?

Its very easy to work out the gender of sexually dimorphic fish, you can simply look at them. The sex organs is shaped different, the size, shape and colour is different. Male fish in sexually dimorphic species are larger than the females.

Sexually isomorphic fish species have few differences, they are very hard to tell apart. Sometimes, the only way to tell these fish apart is to look at their genitalia upon birth.

Check the markings and colourings of the parent fish to make sure they are healthy and mature. You also need to make sure the fish are well tempered and compatible. In certain species, such as cichilds, a pair will only bond together if they have been raised together as a school since they were young. If not, they will fight each other to the death! How kinky.

Once you have selected your pair of fish, feed them the right foods and keep them in the right conditions, make sure they are ready for breeding and hope for the best. A more detailed post on conditioning fish to breeding conditions will be elaborated later.


Its important to consider the conditions of the tank, the breeding environment and the behaviours of individual fish species before they can breed successfully. Some fish species require only a bare tank, some require a separate for feeding, some require a separate tank for raising the spawn and others require special types of plants and water flow.

Make sure you do thorough research before breeding your fish!

Another way to make your fish breed is to increase the temperature of the water by around 5 degrees. This will speed up metabolism and stimulate reproductive behavior.

its getting hot in here…”


Lets look at arguably two of the most popular breeds of fish: betta fish & goldfish and their mating behaviour


The most important prerequisite to mating is correct tank conditions. Things required include a sponge filter, floating plants and newly hatched brine shrimp or any other food that be consumed by the new batch of fish.

Make sure that the water is suitable for breeding and cycled (any nutrients which have been added before have been given time to disperse).

The water in the tank should be heated to around 28 degrees. Make sure every measurement of the water is suitable before you start to breed the fish.


Male betta fish reach their sexual maturity around 100 days, 3-4 months after hatching.

Image result for betta bubble nest

The creation of bubble nests is a good sign that a betta male is ready to breed.

When a betta male and female are placed together, they will usually begin to fight, this is a kinky part of the mating ritual which is about to unfold in your aquarium dungeon. Do not get too distracted by the show, make sure you keep an eye on them and separate them with a nest to make sure they don’t get seriously injured.

A male interested in a female will flare out his gills, spread his fins and twist his body to grab her attention. Once a female is interested in a male, she dances by twisting her body and her color becomes darker.

If a female is ready to mate, she will spend a lot of time hanging around the bubble nest.

The male betta will circle around the female, he will take his time to decide the best positioning. The male & female will engage in intercourse for a few seconds and the female will release eggs afterwards. Every time the male and female undergo intercourse the female will release 10-40 eggs. Males and females will continue to have intercourse with each other until the female has no eggs left.

You must remove the female from the nest once she had laid her eggs! Otherwise she will eat her own eggs.

Once the female has been removed the male will begin to fertilize the eggs by releasing his semen into the tank. The male will collect the eggs, place then in his bubble nest and protect them for 1-2 days, if the eggs become removed from the nest the male will return them.

Remove the male from the nest once the fry (baby fish) emerge.


Just like breeding betta fish, make sure the water conditions in the tank are healthy, meaning that it is adequately cycled and large enough to house adult golfsih.

It is beneficial to have plants and cover for breeding gold fish, the water should be kept around 65 F/18 C for 4 months, to simulate a winter season.

1 month before when you’d like the fish to breed, begin to slowly reheat the temperature to 73F/23C. This will simulate the conditions of spring, the temperature at which the fish breed in the wild, this will initiate mating conditions.

Goldfish reach sexual maturity around 3 years.

Females that are younger can breed with a lower success rate.

A male that is ready to breed will develop white spots along their gills

The female goldfish will become fatter, plumper and more rounded.

The female goldfish will release her eggs upon being chased around the aquarium by male goldfish. The goldfish mating ritual of chasing is very intense, the female goldfish will release her eggs once she becomes exhausted. There is a huge variation between goldfish species but a few thousand eggs will be laid.

Goldfish eggs are sticky, they wil lattach to the plants and the wall of your aquarium, the male will release his semen to fertilize these eggs. The water in your aquarium may become cloudy – don’t worry, this is normal.

Image result for goldfish eggs

^ Goldfish eggs

Once an egg is fertilized it will change color from clear to white. Remove any clear eggs, they will die and rot, polluting your water and bring disease into your aquarium.

It may also be a good idea to move the fertilized eggs into a new aquarium to stop other fish from eating them, fish are very cannibalistic towards their young!


Fish are an extremely diverse group of animals.

Different species have different mating rituals and require different conditions. It is very important to do thorough research if you would like to successfully breed fish.

Goldfish and Betta fish are suitable fish for beginners to experiment with, start with one of the easier breeds if you’re a beginner.




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