Breeding Fish
Aquarium Resources

Breeding Fish

This is an overview about different spawning techniques utilized by fish. Before you embark on a spawning project, it is always a good idea to research your particular species since it is impossible to provide guidelines that will suit all possible fish species within each group.


Livebearers do not lay eggs; they give birth to miniature fish that are free swimming from the start. The male will fertilize the eggs inside the female, just like mammals do. In order to make this possible, his anal fin has been turned into a reproductive organ known as the gonopodium. In some species, the females are capable of storing his sperm and use it for several batches – they can therefore spawn in aquariums even when there are no males present.

The gestation period for livebearers normally varies between 25 and 45 days and by the end of the gestation period, the female can look almost as if she is about to burst. If you look closely, you may be able to see the eyes of the fry through her skin at the base of her tail.

Most livebearers will eat their own fry and if you want to ensure a high fry survival rate you should therefore set up a separate fry rearing aquarium. You can either move the female before she gives birth or net the fry afterwards. If you move the female, she should be moved back to her normal home after giving birth. In some species, a few fry will be born each day over the course of several days. If the male starts to chase the female around right a way, you may have to divide the aquarium or move her to a recuperation aquarium to relieve stress.

For a majority of the most commonly kept livebearing species, a 2.5-5 gallon tank will work great as a fry rearing aquarium. Use water from the big aquarium and install a sponge filter and heater if necessary. Including some plants will make the fry feel more at ease since it will provide them with hiding spots.

The fry of livebearers are normally big enough to eat powdered flake food and newly hatched brine shrimp from the start. Brine shrimps, microworms and other live food will normally ensure a faster growth rate than sticking to nothing by flake food.


The fry of egg-layers are often very small and only able to eat miniscule food, but there are of course exceptions to this rule and the only way of knowing how to properly feed and care for your fry is to research the species. Parental care is much more common in egg-laying species and watching their intricate caring behaviors is truly enchanting. Based on spawning style, the egg-layers are commonly divided into seven different main groups.

Egg scatterers
Egg scatterers are often found in densely grown waters where the eggs will be automatically hidden among plants as they are released by the female. Tetras, Barbs and Danios are three examples of popular aquarium fish that scatter their eggs all over the aquarium. The female will release her eggs while swimming around and the males will follow close behind and fertilize them as they fall. Egg scattering is very common in schooling fish. Egg scatters will not care for their offspring and in many cases the adults will even eat their own eggs and fry. To promote a high survival rate, you must therefore separate the eggs from the adult fish.

Open substrate spawners
Open substrate spawners will pick a certain spawning site, e.g. a flat stone, and deposit their eggs upon it. Open substrate spawners will often form strong pair-bonds and guard their offspring. Examples of popular open substrate spawners are Discus, Jack Dempsey, Oscar and Damselfish. Open substrate spawners do not hide their eggs inside caves or shells, but they can bury them in pits and move them around to protect them from predators. Some species will even pick up eggs and/or fry in their mouths, even though they are not considered true mouthbrooders. Leaving the eggs with the parents is recommended, but there are naturally exceptions. Some species will care for their fry while others only care about the eggs and might eat the fry.

Substrate Spawners that Hide their Eggs
The members of this group will hide their eggs in caves, crevices, shells or similar. If you want them to breed, you must therefore supply them with a suitable spawning site in the aquarium. Just like the open substrate spawners, these fishes often form strong pair bonds and guard their offspring. Examples of commonly known substrate spawners that hide their eggs (sometimes referred to as cave spawners, shell spawners etcetera) are Julidochromis cichlids, Ancistrus catfish and several Dwarf cichlids.

Mop Spawners
Mop spawners are known by this name since they tend to appreciate spawning mops made of yarn as breeding sites in captivity. In the wild, they will naturally use other breeding sites, such as densely grown aquatic plants. The most famous mop spawners are probably the Killifishes from the groups Aphyosemion, Aplocheilus, Epiplatys, Rivukus and Simposonichthys. Compared to the egg-scatterers, mop spawners produce fairly big eggs with hard shells and each batch is much smaller, sometimes consisting of no more than 20 eggs. To ensure a high fry survival rates, most breeders remove the eggs from the mop by hand and raise them in a separate aquarium. Anti-fungal medication can be necessary to prevent fungi attacks.

Peat Spawners
Peat spawners are Killifish species native to areas subjected to severe droughts. The adult fish spawn and hide the fertilized eggs deep down in the mud. If their body of water dries out during the dry season the adult fish will die, but the eggs will stay alive in the mud. Cynolebias, Pterolebias, Nothobranchus and Fundulopanchax killifish are all examples of peat spawning fish. If you want to breed peat spawners, you must provide them with a place to hide their eggs and then subject the eggs to a “dry season”. When you mimic a rainy season, the eggs will hatch and the fish will mature fast since they must be ready to reproduce before the rainy season ends. Peat spawners tend to be short lived, but since they reproduce at such a young age you can let generation after generation inhabit your aquarium. 

Nest Builders
Most nest builders build bubble nests at the surface, but there are exceptions. The nests consist of air bubbles coated in saliva (mucus) and will sometimes include plant matter or be attached to plants. The Siamese fighting fish and all the Gouramis are examples of popular nest building species. Since bubble nests are so delicate, strong water movements in the aquarium must avoided - ideally stick to one, very slow bubbling filter.

Mouthbrooding species will protect eggs and/or fry inside the mouth. Some species carry only the eggs, while some let the eggs hatch at the spawning site before picking up the fry. There are also species that brood both eggs and fry. There exists maternal as well as paternal mouthbrooders. In some species, the brooding parent will spit its offspring when it is big enough and then ignore it, while other species will continue to collect the fry during the night and during the day as well if they perceive any threat. Some will even prepare “baby-food” for their young ones by chewing food and spitting it out.

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