If you think my time and effort in building and maintaining this website is worth a donation, then please use the Donation Button to contribute an amount of your own choosing. May I take the opportunity to thank you in advance for your kind generosity.

• FISHKEEPING VIDEO's
• HOME
• SITE MAP
• A BRIEF HISTORY
• EQUIPMENT
• SETTING UP
• WATER QUALITY
• MAINTENANCE
• FEEDING
• FISHES CATALOGUE
• BREEDING
• DISEASE CONTROL
• LINKS
• FAQ's
• ACKNOWLEDGEMENTS

Fishes Catalogue - Live Bearing Fish Species (Family: Poeciliidae)

Contents

• Swordtails
• Platies
• Mollies
• Guppies

Whenever the term "livebearer" crops-up most people immediately bring to mind species such as Platies, Swordtails, Guppies, and Mollies, after all, it is these extremely popular species that led many people down the road to being dedicated hobbyists, some even building their occupations around the hobby. However, these few species will barely make a scratch on the surface when it comes to adding up the total numbers of livebearing fishes on our planet.

The term livebearer is widely used in the fishkeeping world and is a very general term, it is a method of reproduction not a type of fish and it is not scientifically specific for any particular group of fishes. In the widest definition, a livebearing fish carries the developing embryos within its body until the fry stage is attained and then releases the well-developed young into an environment where they are adapted for survival. They are able to feed and can evade their predators by hiding in tiny cracks and crevices that larger fishes cannot penetrate. Livebearers are not under the same amount of pressure as egg-layers to produce as many young to compensate for predatory loss. Although some female livebearers will produce larger broods of around 150 most normally drop about 20 - 50 young.

Some livebearing species, mainly Poeciliidae, can store sperm for a number of months, a phenomenon known as "superfetation", this means that a single fertilisation from one male will be sufficient to enable the female to deliver several successive broods, the exact number of broods delivered this way will vary from species to species. However, if a female livebearer has been inseminated whilst already having sperm stored in her womb, she will more often than not use sperm from the fresh batch to fertilise her eggs.

The majority of our World's fishes are egg-layers, the females lay eggs that are then fertilised by the male, although there are occurrences in certain species, where the eggs of the female are fertilised by the male, before being released. The problem with this method of procreation however, is that the eggs are vulnerable to all kinds of dangers that can prevent them from developing and hatching out the small fry. That is why nature provides each species of egg-layer with a copious deposit of eggs, in the assurance that some will survive.

In livebearing fishes, and in some egg-layers as previously mentioned, fertilisation occurs internally, and methods have been evolved for introducing the sperm into the female's body. Sharks have evolved a modified intromittent organ for this purpose, from their pelvic fins. In livebearing toothcarps of the Poeciliidae family the anal fin of the male is modified into a similar functioning intromittent organ called the "gonopodium". It is the species of this family that are the better known of all the livebearers and they have become familiar all over the World in the form of Platies, swordtails, guppies, and mollies.

Livebearing fishes may be ovoviviparous, in which case the eggs hatch within the female and the fry are released to swim free. Or, viviparous, where the unborn young are supplied nourishment through the mother's tissues before being "born", in a similar way to most mammals.

1) Ovoviviparous or ovoviviparity means that the eggs are retained within the body of the female and are internally fertilised but the embryos have a yolk sac and develop independently of the mother. The eggs hatch within the body so that the young are then "born alive" but without the strong umbilical or placental attachment, this is also known as "aplacental viviparity." Although the female retains the embryos during the entire time of development, there is no transfer of nutrients to the young; the yolk sac is the only source of nourishment for the developing embryo.

Poeciliidae species such as swordtails and guppies are ovoviviparous.

2) Viviparous species are "truly livebearing", just like our four-legged pets and indeed us humans. The eggs of the fish are fertilised internally and the young develop within the reproductive tract of the female. The nature of viviparity is that the female provides nourishment to the developing embryos, and viviparous fish have developed a number ways of doing this:

a) Nutrition can occur through the production of a nutritive fluid by the uterine lining, which is absorbed directly by the developing embryo.

b) The embryo receives nutrition in a placenta-like way derived from blood vessels, which form a close union of the tissues of mother and embryo.

The families Goodeidae, Anablepidae, and some sharks, are amongst those, which are viviparous fish.

There are currently four families of livebearing fishes:

1) Poeciliidae is the largest of these families and include such species as mollies, Platies, swordtails, guppies, etc. these are the fishes that we are very familiar with, however, there are very many other genus in this family ranging from Alfaro to Xiphophorus and a host of others in between.

Strictly speaking all the livebearers are of the New World, except for the Hemiramphidae, which comes from the waters around South-East Asia, Malaysia, Borneo, Indonesia. The New-World species became synonymous around the World due to their introduction as an aid to mosquito control, in an attempt to eradicate malaria.

Poeciliidae reproduce via the copulatory organ of the male, which is known as a "gonopodium". The structure of this organ can vary within the family and it is these variations that are used to divide up the family into its genus and species. Once the female has been inseminated, some of the sperm will fertilise any eggs that are in her egg sac, any remaining sperm will be stored within the womb ready to fertilise subsequent batches of eggs. This is the phenomenon of "superfetation" mentioned earlier. The gestation period of the females is normally around 28 days. As previously mentioned Poeciliidae are ovoviviparous, the eggs hatch within the body so that the young are then "born alive" but without the strong umbilical or placental attachment.

2) Goodeidae is another family of livebearers known to the aquarist, although not as popular as the Poeciliidae, these too have a modified anal fin, however, it is very different from that of the Poeciliidae species and is called a "andropodium".

For the female to conceive she must lie side-by-side with the male, he will then direct the free-swimming sperm towards her so that it can enter and fertilise her eggs. Unlike Poeciliids, any sperm remaining after fertilisation of the eggs will die off; therefore females require fertilisation for every brood.

Goodeidae are a viviparous family, which means as the eggs develop they will become attached to the wall of the womb by a type of "umbilical cord". This will allow them to receive nourishment from the mother; in turn it means a more developed brood than is the case with the Poeciliidae fry, and, although they weigh heavier, there is less of them. Expect between 5 and 30 fry and a gestation period of 55 - 60 days.

When we refer to the Poeciliids such as mollies, Platies, swordtails, guppies, we use common names that we all recognise, however, the Goodeids (like the Ilyodon, Xenotoca, Ameca) have few common names that we are familiar with and are overwhelmingly referred to by their generic name.

3) Anablepidae is the smallest family of livebearers with only two genus and four species. The genus Anableps has three species, all characterized by large protruding eyes, which are divided by a strip of tissue. The eyes project forward and there are distinctive upper and lower eye parts, for this reason they are commonly referred to as "four eyes".

The eggs of the Anableps take nourishment by being embedded into the wall of the womb.

The remaining genus, and species, is Jenynsiidae - Jenynsia lineatas, and if well cared for can produce 10 - 40 young every 6 weeks. However, this species is rather pugnacious, quarrelsome and cannibalistic and is not a suitable tank mate. It is also susceptible to fish disease, especially tuberculosis.

For reproduction purposes the species of both genus possess a "gonopodium", however, it is quite unlike the gonopodium of the Poeciliids. In this case the males gonopodium is somewhat inflexible and he can only bend it to one side of his body, it is the case that he can only mate on the left or right side, not both. In a similar fashion, the female’s genital opening is either to the left or the right. So, for mating to take place, a left sided male has to find a right-sided female, and visa versa, this is the only way that her eggs will get fertilised. This has resulted in these fishes being named "one-sided-livebearers". However, I have seen it stated, by one authority, that recent research has indicated these fishes can mate on either side, meaning that any male can fertilise any female.

4) Hemiramphidae also known as "Halfbeaks" are lively surface fishes, males will often quarrel and fight each other, which can end up in injury.

Most species of Hemiramphidae are actually egg-layers, however, of those that are live bearing, the milt is transferred by a modified anal fin called an "andropodium", this is similar to the Goodeidae although much more complex. The reproduction cycle is much like the Poeciliids, however, the embryos develop at a different rate and when the fry are delivered they are considerably bigger. As with the Poeciliidae, Hemiramphidae can store sperm, broods vary between species but generally are between 10 and 30, with pregnancies lasting 40 - 60 days.

An elongated body and an extended lower jaw are features that are shared by most of these species, another feature, which is unique to the species, is the combined jaw and the way in which it can be moved in conjunction the skull. Their bodies, with well swept-back dorsal and anal fins, indicate that they are a predatory fish.

• Swordtails
• Platies
• Mollies
• Guppies