``How do fish make babies...and can I watch?''
By "Mr. A. Non c/o Calypso"
Article donated by Gerald Jennings of www.calypso.org.uk
Fish breed in many ways, and yes you can watch. In fact, watching fish breed is one of
the great fascinations in the hobby because there are so many interesting breeding
strategies among fish.
There are two main strategies that fish use: egglaying and livebearing.
Livebearing fish do what the name suggests. The female gives birth to fully formed,
free-swimming young. The female fish is internally fertilized by the male fish, and
carries the fry for about a month before delivering them. Upon delivery, the babies swim
off, hide, and begin searching for food.
Livebearers include the popular mollies, platies, swordtails, and guppies. Other
livebearers are halfbeaks, anableps, and fish in the Goodeid family. They are easy to sex,
as the female is larger, and the male has a rod-like anal fin called a gonopodium that he
uses to internally fertilize the female. After fertilization, the female can produce
multiple batches of babies without a male present.
Egglaying is also what the name suggests: the fish lay eggs instead of giving birth to
little fish. As the fish grow, they hatch into fry with an attached yolk sac, and then
mature into fish. The process usually takes around a week to 10 days, although it can vary
Egglayers have many methods of laying their eggs
Egg scatters usually scatter eggs around weeds, or onto gravel. The male chases the female
during spawning, and the eggs are fertilized as they fall. Spawning runs can be
spectacular to watch since the fish race around the tank and ignore anything else,
including food. Examples of egg scatterers are tetras, barbs, rasboras, and danios.
Substrate spawners are a little choosier about where they put the eggs. They lay eggs
that attach to some sort of substrate. Plants, rocks, wood, and even the aquarium glass
may be chosen as a spawning site. Both fish participate in the egg laying, with the male
fertilizing the eggs as the female lays them. Examples of substrate spawners are many
catfish, some cichlids, and killifish.
Bubblenest builders lay their eggs in a nest of bubbles blown by the male fish. The
bubbles are held together with saliva and look like foam. They tend to attract infusoria
that the babies can eat, and keep the eggs at the surface of the water, where they are
well-oxygenated. The eggs are laid a few at a time, and carefully placed in the nest where
they hatch. Examples of bubblenest builders are bettas and gouramis.
Mouthbrooders actually keep their eggs in their mouths until the eggs hatch. The eggs
are again laid a few at a time, and once the male fertilizes them, the parent doing the
mouthbrooding gathers them up in his/her mouth. That parent eats sparingly, if at all,
until the baby fish are released. Examples of mouthbrooders are male arowanas and female
Marine fish also lay eggs. Some are substrate spawners, but many lay pelagic eggs that
float in the plankton. There the eggs hatch into a larval stage, and the larvae float
freely and eat tiny plankton until they grow into fish. See the Moe reference for a more
Breeding and Agression
``Help! Why have my angelfish (or kribs or African cichlids) started killing
everything in my tank?''
``Why did my female platy just turn around and eat her babies?''
``I think my tetras spawned. Where are the eggs?''
Parental care in the fish world varies widely. Parents can be anywhere on a continuum from
eating all their eggs or fry, to both parents fiercely guarding their eggs and fry.
Many fish parents show some common behaviors, so I will discuss them here.
Most fish consider any and all fish eggs and young to be a tasty treat. Therefore most
fish will not hesitate to snack on any they find, including their own. This means that egg
scatters and many substrate spawners really cannot be bred in a community tank, as the
eggs will quickly be eaten by the parents and other fish. Marine fish and invertebrates
also eat eggs. Livebearers are especially notorious for eating their young.
A few fish ignore their eggs or fry, and so can be bred in a species tank. White cloud
minnows can breed this way, and many killifish will at least ignore the eggs. Baby killies
are fair game, though. Guppies will also often ignore babies.
Other fish have one parent that guards the eggs and fry. Most bubblenest builders and
mouthbrooders operate this way, as do some substrate spawners. The responsible male or
female stays with the eggs and young, until they are free swimming. With bubblenest
builders, the male tends the nest, blows bubbles as they pop, and keeps any falling eggs
or fry in it. He will also defend the nest against other fish. Mouthbrooders simply hide
their eggs in their mouths, and some substrate spawning catfish will hide the eggs
underneath them. Certain substrate spawning cichlids also have one parent care for the
eggs and fry.
A more common setup among cichlids is to have both fish guard and care for the young.
This setup can be really fascinating to watch. The parents will take turns fanning or
blowing fresh water onto the eggs, and removing any fungused eggs. They will also fiercely
defend the spawning site, which can often cause injury or even death to other tankmates.
Once the eggs have hatched, the parents will also guard the fry. Some fish will even move
the fry to a different place each day. Once the babies are free swimming, some fish
continue to guard them, while others end their parental duties. Many African cichlids
guard their babies until they spawn again. Discus even feed their babies off of their
A more extreme version of guarding is practiced by some Tanganyikan cichlids. There,
older siblings will stay around the nest and help the parents defend subsequent spawns.
The babies are allowed to stay until breeding age, when they are driven off.
``My fish just laid eggs. How do I keep the eggs or babies from being eaten?''
The most common way to keep eggs from being eaten is to use a separate breeding tank.
There the parents can spawn or give birth to their young, and be removed once they are
done. Egg scatterers can be placed over a piece of netting, a grate, or a bed of marbles
to protect the eggs as the fish spawn. Bubblenest breeders and mouthbrooders can be left
in the tank until they stop caring for the young. Livebearers can be allowed to give birth
in a dense thicket of plants or plastic spawning grass, so the babies can hide until the
mother is done giving birth and is removed.
A breeding tank also is good because it can be kept clean. Eggs and fry need very clean
water to hatch and grow. There are also no adults around to compete with the babies for
food. Many breeders use a bare tank with only a sponge filter as filtration. Debris and
extra food are easily seen and siphoned off daily. Frequent water changes can be done on
the tank, as there are no other fish around to stress.
Another solution is to allow fish to breed on yarn mops, a plant, or a piece of slate
or glass in the community tank. The eggs can then be moved to the breeding tank to grow.
This works well for angelfish, catfish, and Australian rainbowfish. Killifish eggs can be
collected from peat or yarn mops and set in a separate container or dried to incubate.
Livebearers can be bred in a commercial breeding trap or breeding net within a community
tank. The trap separates the babies from the mothers and then gives the babies a safe
place to grow.
Some cichlids protect their babies well enough to just be left in a community setup,
although this can stress the other fish in the tank. In fact, there are species of
cichlids that will turn on each other if there are no other fish in the breeding tank for
them to threaten.
``I have fish in a breeding setup, but they just won't breed.''
``Why do my fishes' eggs keep fungusing and the fry dying?''
Many fish will not breed successfully without specific requirements. These include:
A mix of male and female fish.
I know this sounds obvious, but some fish are not easy to sex. In species that are
difficult to sex, is best to start out with at least six young fish so that you are
certain of getting both males and females. Starting with many fish also gives monogamous
fish a chance to pick compatible mates. Sometimes if a single male and female are
introduced, they will not breed. Other fish, like livebearers, killifish, and polygamous
cichlids need more females that males so that females are not harassed by amorous males.
Extremely clean water.
Most fish will not breed if there is any ammonia or nitrite present, and large amounts of
nitrate are toxic to baby fish. Some fish, especially tetras, must be bred in a breeding
tank that is bare and sterile so that their eggs do not fungus. For more information about
clean water, see the beginner FAQ.
A varied diet.
Fish that are producing eggs need better food that fish that are just living in a
community. Breeders call the process of specially feeding parents conditioning.
Conditioning foods include live foods, fresh frozen foods, or spirulina based foods. Find
out the specific requirements of the fish you intend to breed. If you need information
about live foods, see the live food FAQ.
The correct environment.
Fish that breed on substrates need proper substrates to breed on, like peat, rocks,
shells, or plants. Some fish are shy and require a lot of cover, caves, or dim light.
There are also fish that require a particular water chemistry to breed. Examples are
discus, which require very soft, acid water or African cichlids which require very hard,
Many tropical fish breed in the rainy season. When it rains, streams flood, the water
hardness drops, and there is thunder and lightning. Adventuresome breeders with rainy
season fish may try large water changes with distilled water, watering cans to simulate
rain, strong currents, and even flashing lights and loud noises. Temperature changes may
also stimulate spawning, as may changes in the light/dark cycle.
``My fish bred, but I cannot raise the fry to adulthood.''
Rearing fish can take some work. Baby fish require clean water, and some require special
Baby livebearers are usually the easiest to raise. Some will take finely crushed flake
foods from the start, and only require frequent water changes to keep up with their
growth. They also need algae or spirulina.
Baby egglayers are often more difficult to raise. Most are too small to eat adult fish
foods, and so require special foods. Live baby brine shrimp are the food of choice for
most baby fish, although some require even smaller infusoria. Sifted daphnia also work.
Baby algae eating catfish require algae or blanched vegetables. There are also commercial
fry foods that work or, in desperate situations, cooked egg yolk. Be careful, though,
because non-living foods pollute the tank water terribly -- especially egg yolk.
Actually, keeping the tank water clean is probably the biggest challenge in raising
fish. The growing fish require lots of food, and they are not very good at finding it
which means even more must be added to the tank. As in any fish tank, adding lots of food
must be balanced with keeping the water quality extremely high. In fact, fry require
cleaner water than adult fish. Frequent water changes are a must, as is efficient
biological filtration. Baby tanks often require daily water changes of up to half the
tank. Sponge filters are the preferred method of filtration because they are great
biological filters but cannot suck up baby fish.
Marine fish larvae have the strictest requirements of all. They must be fed extremely
small plankton or rotifers in a tank with near-perfect water. For more discussion of
marine fish rearing, see Moe.
Finally, as the baby fish grow, they must be transferred to larger quarters. Clearly
the 10 gallon tank that housed 100 fry cannot house those 100 fish for long. Betta
breeders have even more work on their hands, since the little male bettas will fight and
have to be put into separate jars or a partitioned tank.
``I have a ton of baby fish. What do I do with them?''
``Can I make any money breeding fish?''
Finding homes for baby fish can be almost as much of a challenge as breeding them. Young
fish can be given away, auctioned at aquarium society auctions, traded for other species,
or sold. Pet stores will sometimes take African cichlids, guppies, and bettas, but many
only give store credit rather than cash.
As for turning breeding into a commercial venture, remember the laws of supply and
demand. For most common community fish, pet stores can order whatever they want whenever
they want it from importers, fish farms, and wholesalers. The hobbyist, on the other hand,
has occasional batches of fish that the store may not need or want at that time. The only
thing on your side when you walk into a store with a batch of unrequested fish is that
locally bred fish are often healthier and less stressed that fish that have been shipped
and must be acclimated to local water conditions.
If you insist on breeding saleable fish, try rare catfish, rare rainbows, African
cichlids, show quality fancy guppies, or marine fish. Those are all difficult for stores
to obtain. To make money selling more common fish like angels, barbs, tetras, cory cats or
livebearers (other than guppies), you need many breeding tanks and breeding pairs of fish
to assure a constant supply. You must also have fish of consistent quality.
Personally, I would recommend that you breed fish for the sheer pleasure of it, rather
than turning your fun hobby into a business venture. There is nothing like seeing a pair
of cichlids court, disappear into a cave, and emerge in a few days with a swarm of babies.