Different fish species have developed very different reproductive methods. Some lay eggs, while others give birth directly to free swimming fry. Some are devoted and spend a lot of time caring for and protecting their offspring, while others will eat their young ones if they get a chance. Understanding the various reproductive methods is of course very important if you want to become a successful fish breeder.
Types of Reproduction in Fish
As novice fish breeders usually find out sooner or later, there are many fish species that readily spawn in captivity. They do not need any special food, temperature adjustments or aquarium decoration to start breeding – some female fishes do not even need a male partner around to start reproducing!
A majority of these highly prolific aquarium species are livebearers, which means that they directly reproduce free swimming fry. Females from several species of livebearers can store sperm inside the body for prolonged periods of time, and this is how they manage to reproduce even in aquariums without any male.
If your female livebearers start giving birth to fry without any male around, they have mated in the wild or in the pet shop and stored the sperm since then.
A majority of the worlds’ fish species are however not livebearers but egg layers. The egg-laying species can be categorized into four main groups based on their reductive method: the egg scatters, the substrate spawners, the bubble nest builders and the mouthbrooders. There are other ways of categorizing the egg-layers, but these for groups are used by many aquarists.
1. The egg scatters
An egg scattering species of fish simply release the eggs into the water. The male will fertilize the eggs as they are released and the eggs will then either sink to the bottom or stay afloat. This reproductive method is especially common in species that inhabit streams and rivers where the water flow will transport the eggs and distribute them over a larger area. Since these species are not used to having their offspring around, they will often eat their eggs and fry if kept in the same aquarium.
2. The substrate spawners
Substrate spawning fish species do not want their eggs to be transported away by currents. Substrate spawners will therefore often (but not always) produce sticky eggs that can be attached to a substrate. Some substrate spawners will attach the eggs to virtually any surface in the aquarium, while others are extremely picky. If you take a look at the native habitat of the species, you can often figure out which type of substrate they will appreciate. Species living in densely grown waters will often attach the eggs to plant leaves and stems, species in rocky environments sometimes keep their eggs hidden inside caves and crevices, species living near sandy bottoms might dig a pit and place their eggs inside and so on. Flat rocks and empty shells are also popular among many species. Many species will spend a lot of time searching for a suitable breeding site in the aquarium and vigorously clean it before any spawning takes place.
3. The bubblenest breeders
The bubblenest breeders are truly fascinating to watch when they breed since they produce elaborate nests built from tiny bubbles made from air and saliva. It is usually the male fish that is responsible for the construction of the nest. It is very crucial not to disturb the bubblenest in the aquarium. Heavy water circulation can, for instance, need to be hampered to prevent the bubble nest from being crushed.
4. The mouthbrooders
The mouth brooders will protect their offspring in the safest place possible – the mouth of a parent. Some mouthbrooders carry their eggs inside the mouth, whereas others carry their larvae. Some species carry eggs as well as larvae. You will also notice that certain species are maternal mouthbrooders, while others are paternal mouthbrooders. Even if only one parent carries the offspring, it is common for mouthbrooding species to form monogamous pairs where both parents care for the offspring. Mouthbrooding is also frequently combined with substrate spawning. The female can, for instance, deposit the eggs in the substrate, and wait for the larvae to hatch before she or her partner picks them up.
Difficulties & Examples
Some fish species are very easy to breed, while others have very specific requirements. There are also many fish species that have not yet been bred in aquariums. If you are beginner aquarists and willing to try breeding fish, you can ideally start with some of the easier species.
Platy, Guppy, and Molly are almost too easy to breed since they require very little effort from the aquarist. These fish are all examples of popular livebearers. Livebearing fish perform internal fertilization where the male uses his gonopodium to reach inside the female and fertilize her eggs. The gonopodium is a modified anal fin that acts as a reproductive organ. The fertilized eggs will develop inside the body of the female fish. When the fry is born, they will usually look like little copies of their parents. It is however common for fry to have a more camouflaging coloration than the adults, and they can also be without certain extravagant anatomical features that are only useful for mature fish.
If you keep more difficult species, you might need to coax them into breeding. The only way to find out what makes your particular species interested in spawning is to research them since different species have different triggers. Some fish species are for instance very sensitive to temperature changes and increasing (or in some cases decreasing) the water temperature is a good way of coaxing them into breeding. Other fish species will feel ready to spawn when there is an abundance of live food to be found in the aquarium, or when a larger water change alters the levels of ammonia, nitrites, and nitrates in the water. It is naturally always recommended to keep the water quality up, provide your fish with suitable food and make sure that the aquarium is large enough for them. A decorated aquarium resembling the natural habitat of your particular fish is usually a better choice than a barren aquarium if you want your fish to breed. Some fish species have very particular requirements, and will for instance only breed in planted aquariums.
Maintain the water quality up and feed your fish and they will probably spawn sooner or later.
Separating and moving the fry to their own aquarium ensure a high fry survival rate. Instead of filling your entire home with fry aquariums, you can also let the fry stay with the adult fish since this will make the amount of new fish more reasonable. Most of the fry will probably be eaten, but a few will usually survive if you provide them with suitable hiding spots in the aquarium, e.g. densely planted areas or rock formations with small caves and crevices.
You should keep in mind that since these species are so prolific in captivity, pet stores will not purchase fry from you. They might accept your fry for free, but only to use as food for other fish.