Introduction to livebearers
(Livebearers – the essential facts that you should know)
Although a beginner’s fish livebearers have a fascination breeding behaviour and birthing method. The females give birth to live young. Baby fish that are the exact miniature version of the adult. There is also something for the advanced fish keeper. There are other exotic species of livebearer. Good examples are the mexican topminnow and endlers guppy as well as the half beaks. There are many other uncommon species almost as good as the common livebearers.
In the tropical fish hobby, there are four families of live-bearer available.
1. Livebearing tooth carps (Poeciliidae). This is the largest group of live-bearers and includes some well known aquarium favourites. Mosquito fish, guppies, platies, sword tails and mollies are all members of this family. There is an international fish club called “American Live-bearer Association” that is open to livebearer keepers all over the world. There is also a British version available to hobbyists in the UK called “British Livebearer Association”.
2. Goodeidae includes the Mexican topminnow. These are rare livebearers in the hobby.
3. Half-beaks(Hemirhamphidae). These fish are straight long fish with a long pencil like beak shaped mouth. There are 20 species of half beak. Half beaks are occasionally found in the hobby.
4. Four-eyed fish (Anablepidae). These fish are interesting for their ability to equally see above the surface of the water as well as in the water simultaneously. Their eye balls have evolved into two bulbs with the upper part of the eye above the waterline and the lower part under the surface. They are incidently livebearers.
Where are livebearers found in the wild?
Live bearers are mostly from the Americas but some species are found in Asia. Their range extends from north America to Argentina in South America. Most livebearers eat mosquito larvae especially the mosquito fish. This ability of livebearers to eat lots of mosquitos and breed rapidly led them to be used in coutries with mosquito and malaria epidemics in S.E. Asia and the Philipines. However, these livebearers were so successful that they spread all over sub-tropical and tropical asia and even into parts of Southern Europe.
Goodeid livebearers (Mexican Topminnow) live in the rivers and lakes of the Mexican plateau and all the way down the rivers that lead into the Pacific.
Halfbeaks are found all over S.E Asia and can be found in both fresh and brackish water.
Four-eyed fish are found all along the west coast of South America. They are nearly always found in brackish water.
Livebearers’ early history
European aquarists started keeping livebearers from 1890 onward. They were in popular demand when they first appeared because they gave live birth. Because of their popularity they were very expensive. Prices quickly fell when hobbyists started breeding them and selling on the young. Livebearers have always been easy to breed in the aquarium so became widespread throughout Europe.
Livebearer social and reproductive behaviour
Most live bearers are shoaling fish, so do best in a group of 6 or more fish. This group or shoal of fish will develop a pecking order of dominance where an alpha male will dominate other males. The alpha male will show off brighter colours and display his fins better that the subordinate males. The dominant fish will always get to the food first. He will either chase away others or they will retreat as he approaches. The alpha male will always get a better chance to mate with the available females. The females will be more likely to accept him as a mate and he will chase off rival males too.
Most livebearers are non-aggressive community fish but the males may get territorial. Also larger species such as mollies can be boisterous to timid tank mates. Swordtail males are the most aggressive to each other. Keeping 2 or 3 will lead to bullying and death of the weaker males. Surprisingly keeping 5 or more males does actually reduce the bullying against weaker males because the bullying is spread around. Always keep more females than males. A ratio of 2 females to each male is a good starting point to reduce male attention to manageable levels.
Nearly all livebearers do not recognise their young. They will eat any young that appear in their tank as if it was a form of live food, even when it is their own young they are eating.
Courtship behaviour of livebearers
Guppy and swordtail males are very flirtatious and ardent lovers. Males will swim back and forth in front of the females while flexing their bodies in display to the female.
male mollies will present their bodies in front of a females and then spread their fins to their full extent so that the female gets a good display before trrying ti impregnate her.
Other species have a wham bam, thank you ma’am method of mating. The males will lie in hiding waiting for a suitable female. When a female passes by the male will pounce and mate by inserting his gonopod into the females opening and fertilising her.
Some species of livebearers have males that have a hook on the end of their gonopod so that it firmly attaches to the female’s opening while he is inseminating her as she struggles to get away. Not every mating results in successful fertilisation of the female. The ratio is about 10% chance of success. So the males are always trying to repeat the process to guarantee fertilisation of the female.
If the female is not interested in mating she will make a determined effort to escape the male’s attention. Since males are nearly always trying to mate and you might get several males trying to mate with a single female, it is best to provide several females for every male while also providing bushy plants for the females to hide in when they need a break.
Reproduction in livebearers
Livebearing is the most advanced form of reproduction. It is almost universal in all species of mammals. In reptiles and fish it does occur in the occasional species. Most fish species lay many eggs which are fertilised by the males in open water. The livebearers have developed internal fertilisation of the eggs with hatching of the eggs internally. Most species of livebearers eggs hatch shortly before birth and young fully formed livebearers which are miniatures of the adults ae born.
In Goodeid livebearers, reproduction is even more evolutionary advanced. The eggs hatch early internally and the young embryos develop internally and nourished through a form of attached umbilical chord, which is similar to mammals.
Some species of livebearers have females that can store sperm internally following a successful mating. The stored sperm not only fertilises the present batch of eggs but also can fertilise future batches of eggs as they develop following a pregnancy. It was demonstrated in an experiment that a mosquito fish from one fertilisation was able to produce 11 broods one after the other for a period of a year without any access to a male mosquito fish.