The concept of livebearers
Livebearers will not lay eggs, but give birth to free-swimming offspring. The eggs have been fertilized inside the body of the female and the offspring has developed inside of her until they are large enough to be born. This section contains information about livebearing fish. Seahorses and pipefish are sometimes considered to be livebearing species, but you will find information about them in the Marine Aquarium sections instead.
Livebearing are found in several fish families. A lot of the most commonly kept aquarium species belong to the family Poecilidae. This large family contains such popular species as the Platy, Guppy, Swordtail and Molly. Livebearers from other families than Poecilidae are also sometimes kept by aquarists, but they are much rare. Halfbeaks, splitfins, freshwater stingrays and the “four-eyed” fish known as Anableps anableps,are all examples of livebearers from other families that can be kept by more experienced aquarists. You can keep wild caught livebearers as well as cultivated domestic species. The cultivated varieties are often equipped with features that would make them an easy target for predators in the wild and they can therefore only survive in .
A lot of the popular beginner fishes for novice aquarists are livebearers and livebearers are known to spawn in captivity even when kept by less experienced aquarists. There are naturally exceptions to this rule and some livebearers are very hard to breed in captivity. They might for instance require a very particular diet or . In some livebearing species the females will often miscarry and give birth to the embryos to soon.
Since the male livebearer has to fertilize the eggs while they are still inside the female, all male livebearers have developed some form of reproductive organ that can be inserted into the female. Depending on the specific species, you will find one of two different forms of reproductive organs on the male livebearer. If you keep a livebearing tooth carp, the reproductive organ on the fish is called Gonopodium. If you keep livebearers from the families Goodeidae and Hemirhamphidae, the reproductive organ will instead be named Andropodium. One of the main differences between the two variants is that an Andropodium will fold when the male inserts it into the female, while a Gonopodium will flip forward.
Livebearers belong to many different families and are found in various environments in different parts of the world, and their requirements and behavior therefore will naturally vary from species to species. There are however a few general rules that are true for most livebearers. You should always research your particular livebearing species as well, since it might one of the exceptions to the general rules. Generally speaking, livebearers are schooling fish and they will therefore do best in your aquarium if your buy at least four specimens. A male livebearer can be quite aggressive towards other fish of the same species, and keeping one male with at least three females is therefore a good idea. When there are several females, the amount of harassment will be spread out over several individuals and each female will be less stressed. A majority of the livebearing species will prefer where the pH is between 7.0 and 7.8. The water should be hard or medium hard.