In this article, we’ll be taking a closer look at the livebearers, or fish that give birth to live young. Despite the popularity of the goldfish and betta fish, many aquarists have neither of these as their first. Instead, that honor usually belongs to a guppy, or molly, or one of the other livebearers.
The article will be treated as a family review since most livebearers belong to a single family: the Poeciliidae. However, we will also discuss a few separate instances of livebearers relating to other families.
Fact Sheet
| Common Name | Livebearers |
| Latin Name | Poeciliidae, Anablepsiidae, Hemiramphidae |
| Size | 2.5 – 20 cm |
| Place of Origin | South America, North America, Asia |
| Temperament | Mostly peaceful; some exceptions |
| Water Level | Mostly mid-level |
| Tropical / Coldwater | Mostly tropical, some exceptions |
| Preferred PH | Slightly acidic, some exceptions |
| Soft / Hard Water | Generally soft, with some exceptions |
Natural Habitat
For the most part, livebearers can typically be found in slow-moving, or even stagnant, water sources. These include dams, small streams, ponds, and even swamps.
Some species, like the guppy fish Poecilia reticulata, are incredibly adaptable. Such is the nature of this fish that it was used as a form of mosquito control in the past.
The British government would often import this fish to colonies, and release it in local water sources. It was thought that the guppy fish was more adaptable, and hence a better control agent for mosquito larvae.
The ploy was not entirely successful, and malaria continued to rage rampant in British colonies around the world. That is not to say, however, that the guppies were unsuccessful. Indeed, the fish themselves were so successful that they are now a naturalized species in large parts of the world.
Another species that was similarly used is Heterandria formosa, the aptly named mosquito fish. This fish was also successful in world domination and lives throughout the world’s tropical and subtropical areas.
To emphasize precisely how adaptable some of these species can be, we must tell you about some places where the guppy fish has been found. Guppies are often found in estuaries, and other unusual places, where the salinity is exceptionally high. Laboratory tests have found that this species can even survive and breed in water up to 150% as salty as ocean water.
The adaptable nature of many species has had some awful results. Irresponsible fishkeepers sometimes release unwanted pet fish into local waterways, and then there were the attempts at using livebearers for mosquito control.
In Africa, the guppy and mosquito fish have taken over many small waterways. The introduction of an exotic livebearer usually leads to the displacement of small native species. Typically, small species like killifish and topminnows suffer most.
Natural Distribution
Although the guppy and the mosquito fish are now distributed worldwide, most livebearers have a small natural distribution.
The most significant percentage of species that we maintain in captivity today originate in the Americas. More specifically, the majority come from South America.
It is the Amazon rainforest that is to blame for most of the beautiful and colorful species that we know and love. The mollies, swordtails, platies, and guppies all originate from this region. The four-eyed fish is yet another livebearer that hails from South America.
North America has donated the butterfly goodeid and the mosquito fish.
Asia has also contributed a few species, specifically the various species of halfbeak. These fish hail from Thailand, Laos, Cambodia, Vietnam, the Philippines, and beyond.
Africa and Oceania, while hosting many egg layers in the same family as the guppy fish, have not had any livebearers to contribute to the trade. We will take a closer look at the egg-laying fish in this family in a different article.
Feeding Habits
These fish are like that one person you always find at every dinner party, they’ll eat just about anything – and a lot of it. If it’s big, they will nibble at it. If it’s small, they will gulp it.
They will nibble at the plants that you haven’t intended to feed them (aka the ones that make your tank look nice). However, they will love you for feeding them blanched lettuce and other leafy food.
There are some notable exceptions. The halfbeaks, for example, will shun prepared and frozen foods and insist on eating live foods. Failure to provide these species with appropriate live foods will result in your fish pining away.
Most of the rest of the livebearers will eat prepared foods and unprepared foods. However, even for them, the real bane of every livebearer’s existence is live food.
Be sure to feed them regular portions of live foods like mosquito larvae, bloodworms, and tubifex worms.
Smaller livebearers like mosquito fish, and the fry of larger species, will also benefit from regular feedings of small live foods.
Because livebearers reproduce so readily, they require the protein provided by live foods to help keep them healthy. After all, a lot of energy and nutrients go into breeding.
Breeding Behaviour
The breeding behavior of these fish is probably the most noteworthy feature. Despite their adaptability, colorful appearance, and easy care, it is usually the breeding behavior that attracts people.
Much like people, and other mammals, these fish give birth to live young. However, unlike mammals, giving birth is not the right phrase. As with all fish, female livebearers produce eggs, and male livebearers produce sperm.
However, their breeding process is significantly different. Before we delve into the process, let’s look at the differences between male and female livebearers.
Sexual Dimorphism
In most livebearers, the anal fin varies vastly between males and females. Females have the typical, fan-shaped anal fin that we all know and love. Look at this female Platy, for example.
Females are often also drabber than males. Female Guppies, for example, only have color on their tail fins. Male Guppies, by contrast, are entirely colorful.
In the Swordtail, Xiphophorus helleri, males sport a long extension to their tail fins. Females, however, lack this appendage. Of course, the strange sword-shaped fin is what gave them their name.
In many other livebearers, there is a significant size difference between the two genders. In the wrestling halfbeak, Dermogenys pusilla, the female is almost three-quarters of an inch longer than the male at adult sizes.
Ahsan_al_hidayat / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)
Nonetheless, the most conclusive feature separating male and female livebearers remains the anal fin form. We have already established that in females, the anal fin is relatively standard.
However, in male livebearers, the anal fin is usually adapted into a tube-shaped fin called a gonopodium. In the halfbeaks, this fin is called an andropodium.
The reason for the adaptation of this fin is that, as in mammals, male livebearers fertilize the eggs within the female body.
One notable biological adaptation has taken place in one of the few livebearers in captivity that is not a member of the family Poeciliidae.
In the four-eyed fish, Anableps anableps and Anableps microlepsis, the male gonopodium has adapted to be either right-handed or left-handed. Similarly, the female genitalia is either right-handed or left-handed.
Consequently, right-handed males can only breed with left-handed females and vice versa. Scientists are at a loss as to what the advantages could be of this mating system. One theory is that it may prevent inbreeding between siblings.
Egg Development
Unlike hot-blooded animals, there is no physical connection between the offspring and the female body. Also, no feeding takes place within the female body as would occur via the umbilical cord in mammals.
Instead, the female’s body is simply an incubator where the fish fry (aka baby fish) can develop safely. Once the fry have developed completely, they hatch from the eggs, as they emerge from the female’s body.
In rare cases, females may abort batches of eggs, or release them prematurely as unhatched eggs. This is usually as a result of health issues or a stressed-out female.
One of the reasons this is such a popular group of fish is that, in most thinner-bodied species, it is quite easy to tell when a female will give birth.
The female develops a darkened spot on the back of her abdomen. This is known as the gravid spot, and increases in size and intensity as the birth draws closer.
This black spot is the result of the eyes of the fry becoming larger. As they increase in size, the combined black color of all the fry shows through the female’s thin body wall.
In most of the standard livebearers, the average gestation lasts for 3 to 4 weeks. However, in some of the species not in the family Poeciliidae, the gestation may be 6 to 7 weeks. This is the case with the halfbeaks and the four-eyed fish.
Raising fry
If you want to raise any of your livebearer babies to maturity successfully, you have a difficult choice.
Apart from the fact that females carry the eggs within them for a month or more, these fish have no parental instincts.
Anything that fits in their mouth and moves they will eat, and that includes their babies.
So if you are intentionally breeding any sort of livebearer, you will have to set up a system for raising the babies.
First and foremost, you have to offer them some sort of cover so they can hide after they are born. One method that works well is to scatter a layer of marbles on the tank’s base, providing many nooks and crannies for them to hide in.
A planted tank with thickets of small-leaved plants is another viable option. A popular choice is the breeding cage, which is a simple plastic or fabric box. You use it to separate a gravid female, in anticipation of the arrival of babies.
However, such a system is often stressful for the female and may cause problems.
If you are truly set on saving the fry, it is much better to set up a small aquarium where you can place the female about a week before you expect babies.
That way, she will be a lot less stressed, and you will also have a place to raise the babies until they are large enough not to get eaten by the other fish.
The fry themselves are easy to raise and will readily eat crumbled flake food or pre-made prepared foods for fish fry. They will benefit from the addition of brine shrimp nauplii to their diet, as well as daphnia.
Size Variations
For the most part, the livebearers are standard small to medium-sized fish. The largest species in this group of fish grows only to about 20 centimeters.
On the other side of the spectrum, the lesser mosquito fish grows only to about 2.5 centimeters.
On average, though, livebearers are between 5 and 7 centimeters in length.
Conclusion
We hope that you have enjoyed this basic article about the livebearer group. Even though it is a small group, there is still a vast amount of information to cover.
Therefore, if you would like to know more about any specific species, please head over to our species profile for that fish. You will also find profiles on other livebearers that are equally wonderful but have not been mentioned here.
