How do fish breed?

In this brief article, we will answer the question, “How do fish breed?” and provide information on the types of oviparous fish, reproductive organs of fish as well as how ovoviviparous, viviparous, unisexual, and hermaphrodite fish reproduce.

How do fish breed?

Fishes can breed by laying unfertilized eggs in water. When these unfertilized eggs are put in water, the males lay a cloud of sperm on top of the eggs to fertilize them. 

Sometimes, the cloud of sperm might already be present in the water and the female might lay eggs directly on them to fertilize them. The eggs might then sink or float before it is about to hatch.

If the eggs float prior to hatching, they are called pelagic. Pelagic eggs tend to be lighter and float on water.

If the eggs sink prior to hatching, they are called demersal eggs. These eggs are heavier and are also adhesive. Once these eggs sink down, they might stick to certain structures or areas because of their adhesion. Such fishes that lay eggs to reproduce are called oviparous.

Oviparous fish usually lay many eggs at a time. This is because it can take a lot of time to lay eggs. The weight and size of the female fish can determine the number of eggs that she can lay at a time.

Sometimes, fertilization in oviparous fish can occur in a different manner. Some fish lay eggs and the male fish fertilizes them by rubbing their reproductive organs on the fish.

What are the types of oviparous fish?

Oviparous fish are further classified based on how they lay their eggs:

  • Mouthbrooders are fish that lay eggs in water and then keep them in their mouth once the eggs get fertilized. This can protect their eggs from predators. Examples of such fish are cichlids, bettas, and gobbies.
  • Nest builders are fish that build a nest before laying eggs. The female and male fish build the nest from plant materials and other organic matter. 

Once they have built the nest, females lay them and the male fertilizes them. Gouramis and bluegills are some examples of such fish.

  • Egg scatterers are fish that lay sticky eggs and non-sticky eggs. Sticky eggs are laid under water whereas non-sticky ones float. 

The males can fertilize all these eggs by spraying semen from their sexual organs. Examples of such fish are Tiger bards, koi, and goldfish.

  • Egg depositors are fish that lay eggs in one area (away from predators) and the males come and fertilize them. Some examples of these fish are clownfish and killifish.
  • Egg burriers are fish that buries the eggs and the males would come to fertilize them. Killifish is an example of such a fish.

What are the reproductive organs of a fish?

Male fish has testes while female fish has ovaries. Some fish have a genital papilla which is a secondary reproductive organ. Some fish are hermaphrodites (have both male and female organs). Hermaphrodites are capable of reproducing themselves.

How do ovoviviparous and viviparous fish reproduce?

In ovoviviparous fish, the eggs are produced inside the mother’s body which is fertilized by the male’s anal dorsal fin. The sperm are released into the female’s body from the fin. The young ones present inside the eggs derive nutrition from the egg yolks. 

In the case of viviparous fish, the fertilization and development of young ones take place inside the female fish’s body. However, unlike ovoviviparous fish, the young ones obtain nutrition from their mother. Once the young ones are fully developed, the mother gives birth to them.

Are there unisexual fish present?

Some female fish can reproduce by themselves without a male. These female fishes can give birth to young ones. They might mate with males but sperm is not required for fertilizing eggs. 

How do hermaphrodite fish reproduce?

Hermaphrodite fish are able to change their sexes to lay eggs. This means that a female fish can become male and vice versa. 

However, even if a male becomes female or vice versa, they might still need a fish of the opposite partner to reproduce.

This can be observed in clownfish. A clownfish’s group consists of a male, a female, and other small males. When the female leaves their group, their male partner becomes female and the next biggest male fish in the group can become their partner.

Some fishes like Mangrove killifish can produce eggs and sperms at the same time. Both male and female organs in such fish function at the same time.


In this brief article, we have answered the question, “How do fish breed?” and provided information on types of oviparous fish, reproductive organs of fish as well as how ovoviviparous, viviparous, unisexual, and hermaphrodite fish reproduce.


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