Fish Spawning Methods

Fish Spawning Methods

A majority of the world's fish species are egg layers, but there are also a lot of species that have developed into livebearers. The egg laying species will typically use some form of external fertilization of the eggs, while the livebearers perform internal fertilization. The level and type of parental care will also vary considerably between different fish species. Some are extremely devoted parents while others leave their offspring immediately, or even worse – try to eat them! The parental care can also vary a lot between different individuals within the same species, and from batch to batch.


Livebearing fish species give birth to free swimming fry. A lot of the commonly kept aquarium species are livebearers, such as the Guppy. The eggs are fertilized by the male while they are still inside the body of the female fish, so called internal fertilization. In livebearing species, the male's anal fin has developed into a reproductive organ. This type of modified anal fin is called a gonopodium. After the fertilization, the eggs develop into fry inside the female fish. When the fry is born, they look like miniatures of adult fish, but sometimes without the striking colours of their parents. Many species develop striking colours as they grow larger and mature. In some livebearing species the female fish can store spermatozoa (semen) from one single mating and use it to fertilize several batches in a row. This is why female livebearers sometimes give birth in aquariums where they are kept without any males.

Egg scatterers

Egg scattering species are often living in fast flowing waters in the wild. The eggs are released by the female and fertilized, and then rapidly swept away by the current. This is why egg scattering species will usually eat their own offspring if they spawn in aquariums. If you are planning to breed an egg scatterer, e.g.a Zebra Danios, you must protect the eggs from the parents. You can cover the aquarium floor with marble and keep the water shallow. The eggs will sink and since the water is shallow they will rapidly reach the bottom, where they will lay hidden among the marbles. Larger marbles will also provide hiding places for the fry when they emerge. Some breeders place a net in the aquarium, to prevent the adult fish from reaching the bottom. The mesh must be large enough for the eggs to fall through.

Egg Depositers

There are two types of egg depositers: open water spawners and secretive spawners. Open water spawners will not hide their eggs. Open water spawners typically deposit the eggs on a flat rock, on the aquarium floor or on the leaves of broad leaved aquatic plants. Some open water spawners will dig a crater in the substrate and place their eggs inside. Secretive egg depositers wants to hide their eggs, and will choose a cave, a crevice or similar as spawning site. In the aquarium they will usually appreciate turned over terracotta flowerpot. Both open water spawners and secretive spawners clean the site before they deposit their eggs, and they will usually also defend the eggs and care for them by cleaning them. Before the fry emerge, many egg depositers will move the eggs around to other pre-cleaned sites. Egg depositers are also known to guard their fry and the fry is often seen swimming around with their parents.

Nest Builders

The nest building group is actually a sub-category to the egg depositers. Nest builders create nests of bubbles and deposit their eggs inside. The nests are formed by the male fish by blowing saliva bubbles, and a bubble nest will often contain plant fragments. When the female has released the eggs they are carefully gathered by the male and placed inside the bubble nest. In some species, the female will gather the eggs. In some species the eggs will float up into the nest without help from the parents.

Mouth brooders

Mouth brooders are also a kind of egg depositers, but the offspring is guarded inside the mouth of a parent. The eggs are often deposited in a shallow crater where they are fertilized by the male before being picked up by the male or the female fish. In some species the eggs are fertilized by the male when they have already been picked up by the female. Some mouth brooding species will carry only the eggs inside the mouth and spit out the emerging fry, while others will care for the eggs on the spawning site and pick up the fry with their mouth when they emerge. Some species will carry both egg and fry. Even after being released, the fry might flee into the mouth of their parent if they are scared by something or sleep inside the mouth during the night.

Egg buriers

The egg burying species have developed in areas subjected to seasonal draughts. During the rainy season, the eggs will be deposited deep down in the mud. The eggs will then stay buried during the draught. When a new rainy season begins, the water will trigger the hatching of the eggs and fry will emerge. The egg burying species will not guard their offspring, since the parents are usually dead long before the rainy season begins. If you want to breed egg burying species in your aquarium you must simulate a dry season and a subsequent rainy season. The adult fish can be given a container filled with peat moss to deposit their eggs inside instead of placing them in mud. The container can be removed from the water and subjected to a several month long dry season in a cupboard. Once you add water to the peat moss again, the eggs will hatch and you can start feeding the fry.

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