Freshwater Breeding

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Yellowface Marlboro Discus with with fry.


Modes of Reproduction

In Tropical Freshwater Aquarium Fishes
By Kathleen Wood
from The 101 Best Tropical Fishes

For many freshwater aquarists, one of the joys of keeping exotic fishes is to encourage and witness the reproductive lives of their fishes. Unlike many marine species, which can be challenging to spawn in home-scale aquariums and which often produce exceedingly tiny, hard-to-feed larvae, many freshwater species are not especially difficult to breed. In fact, in many cases, such as the livebearers and cichlids, it may be virtually impossible to keep the fish from doing what comes naturally.

Aside from the satisfaction that breeding your aquarium residents provides, there are a variety of other motivations. Some enthusiasts are able to support their hobby by offering the progeny of favorite fishes for sale to other aquarists or local aquarium stores. Still others breed their fishes to witness the incredible repertoire of interesting behaviors associated with courtship, spawning and fry rearing exhibited by a wide array of fishes, such as the cichlids. And finally, there are those who breed their fishes in search of the “perfect” specimen to display at various fish shows.

As with all living things, breeding is about nothing less than the survival of the species. To that end, freshwater fishes have developed a number of strategies to assist them in this effort. Most freshwater fish reproduce sexually, and can be divided into two main categories, based on their reproductive styles: those that give birth to live offspring and those that lay eggs. With the first group, the reproductive process is more-or-less simple and straightforward, although there are instances where the process is a bit more complicated. Among the egg layers, however, the variety seen in their reproductive strategies is astonishing at times. At the simplest level, there are those that release eggs and sperm directly into the water where they are fertilized and fall to the bottom (or in some cases rise to the surface), or those that deposit their eggs on some type of substrate. There are also those that brood the eggs in their mouths. Here is a brief introduction to the modes of reproduction you may witness in your aquarium.


The livebearers, most famously the guppy, mollies, platies and swordtails, produce eggs that are fertilized and then develop internally in the female until she delivers fully developed baby livebearers after a brief period. The male livebearer fertilizes the eggs by using his modified anal fin, called a gonopodium, to deliver his sperm directly into the female’s reproductive canal.

Livebearers practice no parental care and the fry are basically left to their own devices and are at the mercy of the elements. If special precautions are not taken in the closed confines of an aquarium, most of these tiny livebearers will become food for the other tank inhabitants, including their parents, which are often first in line at the buffet.

In the wild, a similar situation occurs, although the chances of more fry surviving are somewhat better just by virtue of the fact that there are more areas for them to find refuge. The aquarist wishing to raise the fry must remove them to a separate rearing tank to prevent their being eaten or isolate the gravid female in a breeding trap or a heavily planted aquarium.

Curiously, many female livebearers are able to store sperm internally and use it to fertilize additional batches of eggs over a period of several months. It isn’t unusual for a female guppy, for instance, to give birth to baby guppies even though there are no other guppies in the tank!

Egg Layers

In this mode of reproduction, for the most part, the eggs and sperm are released into the water where fertilization then takes place. There are, as you might expect, many variations on this theme. In some species, such as the South American Zamora Catfish, the eggs are internally fertilized before they are deposited. In the egg scatterers, the process is so quick that it is often over before you know what has happened. Female egg scatterers release their eggs into the open water, usually at the mid-water to top levels of the tank, with the male releasing a cloud of sperm at the same time—the eggs are fertilized and their job is done. The eggs drift up into floating plants or down among pebbles, rocks and grasses. Some eggs remain loose, while others are adhesive and designed to cling to plants until hatching. The egg scatterers typically practice no parental care and the pair quickly join the other inhabitants of the tank by feasting on their progeny. Hobbyists who wish to breed these fishes will need to take precautions to protect the eggs. Success means setting up a separate breeding tank and then removing the pair once the eggs are scattered. But sometimes in a heavily planted community tank, some of these tiny fry may escape predation and be seen hiding among the plants or in a crevice. This is always a thrill.

Some egg layers are a little more selective and deliberately deposit their eggs on or in a particular site. The popular Corydoras catfishes will place their larger adhesive eggs either singly or in groups on plants or aquarium equipment or glass. Other egg layers display more complex methods of reproduction. In many substrate-spawning cichlids, male and female form a strong pair bond and will lay and fertilize their eggs in a protected area and then defend them against all comers (including the aquarist’s hand or a net).


Other cichlids, a number of anabantids, and even some catfishes, practice mouthbrooding, in which the eggs are picked up and carried in the mouth of one, or both, parents after spawning. There is a great degree of variation in this reproductive style. Most familiar to aquarists are the maternal mouthbrooders. All Lake Malawi cichlids typically seen in the hobby practice this style of breeding. The females pick up the eggs, which may be fertilized externally or in her mouth, and keep them in their mouths until the young fish are fully developed. In many species, the fry will continue to return (or at least try to do so) to the female’s mouth for protection even after they are completely developed. In a few other species, the male broods the eggs and in yet others, both parents share the egg-holding duties by passing them back and forth. Most of the mouthbrooders practice some form of parental care after the fry are hatched.

Bubblenest Builders

Nest building is also seen in quite a number of fishes, most notable among these being bettas and gouramis, which create bubblenests. These nests are produced by the male using special secretions to extend the life of the bubbles he produces. This is an on-going process and once the male is in a nest-building mode, he will continually repair the nest and add new bubbles. Often, small amounts of plant material, also gathered by the male, will be incorporated into the nest to help hold it together. Once the male has constructed the nest, he will begin courting a female and spawning will take place. The male then gathers the eggs and places them in among the nesting materials (bubbles and plants). Once spawning is completed, the female should be removed from the tank, as the male will view her as a threat to “his” eggs.

Feeding the Fry

Most livebearer babies and the released young of mouthbrooding cichlids, for example, are large enough to accept flake foods run through a coffee grinder (dedicated for just this use) until they are extremely fine as a good first food. There are also a number of commercial liquid and fine flake fry foods available for just this purpose. These can be supplemented with some meaty foods, such as newly hatched brine shrimp (Artemia nauplii).

The fry of most egg layers will not need to be fed until they are free swimming, as they will continue to feed on an attached egg sac until it is used up. The initial free-swimming fry are quite small and will require correspondingly small foods. Again, there are a number of liquid and fine flake fry foods that will do quite well.

Some aquarists may want to culture their own foods, such as “green water” (unicellular algae produced by placing a jar of fertilized water in a sunny spot) or “Infusoria” (microorganisms and algae that develop from rotting vegetable or plant matter, again, in a separate container). Even bits of hard-boiled egg yolk can be offered. Again, most of these foods are also available in commercial versions. Many of these foods can quickly foul the water. Remember to pay careful attention to water quality in the fry-rearing tank and remove any uneaten or rotting foods.

From: The 101 Best Tropical Fishes