Quick guide to livebearers

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Dr Heok Hee Ng explains why livebearers from the Poeciliidae family are so well suited to fishkeeping newcomers.

Only a few fish feature consistently when the words ‘beginner’ and ‘aquarium’ are mentioned in the same breath. There are the obligatory goldfish, along with the occasional Siamese fighter. There’s also the guppy (Poecilia reticulata) — the little fish named after the person who incidentally was not the first to discover it!

Along with the related Swordtail (Xiphophorus helleri), platy (Xiphophorus maculatus) and molly (Poecilia sphenops), the guppy belongs to the family Poeciliidae — a group commonly known as the livebearers.

The term can be confusing. Although it is usually taken to mean only the livebearing toothcarps — fish in the order Cyprinodontiformes in the families Poeciliidae, Goodeidae and Anablepidae — as well as halfbeaks (the family Hemiramphidae in the order Beloniformes), the term has also been used for all fish giving birth to live young.

Using the latter definition would include a whole slew of disparate marine and freshwater fish whose only common theme is this unusual mode of reproduction.

Poeciliids 

Because this guide is aimed at the beginner fishkeeper, the term is restricted here to certain members of the family Poeciliidae. This is because, among all the fish groups mentioned, they are the most easily available and easiest to maintain in the aquarium.

Poeciliidae consists of 37 genera and about 330 species, and distributed from the eastern United States to South America and Africa, including Madagascar. Despite their common name, not all poeciliiids are livebearers. All 80 African species in 12 genera lay eggs, as do the six species in two American genera of Tomeurus and Fluviphylax.

The African poeciliids and the South American Fluviphylax are not internally fertilising, but males in all of the remaining American species fertilise the female via the gonopodium, which is an inseminating organ modified from the third, fourth and fifth anal fin rays. We’re concerned in this feature only with the internally fertilising American species that bear live young.

Livebearing poeciliids, with few exceptions, are generally found in moderately hard to hard water of about 10–30 GH). A few species are also found in brackish water.

Plant matter, such as algae and diatoms, features prominently in the diet of many livebearers. Although they are not picky eaters and readily take prepared, frozen or live food, an optimal diet should be biased towards plant-based foods such as raw algae, chopped-up greens or even algae wafers.

Livebearers are generally peaceful enough for most community tanks, although males of some species tend to be aggressive towards each other and it may not be a good idea to keep more than one in the same tank.

Despite suitability for the community tank, there are still considerations worth deliberating over before heading for the nearest shop and dumping a bunch of livebearers in your tank.

Remember that livebearers are not big fish, particularly guppies, so mixing them with fish that may consider them food is not a good idea. Some livebearers, such as guppy varieties and Sailfin mollies, have long finnage that may become targets of fin nippers such as bettas, barbs or tetras.

Tank mates should be planned with the optimal water conditions for livebearers in mind.

Although most livebearers featured here are quite hardy and will tolerate most water conditions, this should not be considered licence to completely ignore water chemistry.

Although bottom dwellers such as smaller catfish like Corydoras and loaches have been touted around as ideal companions, remember that the medium-hard to hard water considered optimal for some livebearers is not for most catfish and loaches.

How the guppy got its name

The guppy was named after Robert John Lechmere Guppy, the person who first discovered it on the Caribbean island of Trinidad. Contrary to popular belief, Guppy was not in fact a clergyman but a civil engineer by trade and also an amateur naturalist.

He sent specimens of guppies collected from Trinidad to the British Museum (Natural History) where they were thought to belong to a new species by ichthyologist Albert Günther who named the species Girardinus guppii.

It was later discovered that the German naturalist Wilhelm Peters had described the guppy from specimens collected in Venezuela and he named the species Poecilia reticulata.

Because of the rules of zoological nomenclature, the valid scientific name for the guppy is Poecilia reticulata, but the species name of its junior synonym has survived to become the common name we are so familiar with.

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Platy (Xiphophorus maculatus)

Another species suitable for the community tank due to water requirements overlapping with most aquarium fish. The platy is best maintained in a neutral to slightly alkaline (pH 7.0-8.2), medium-hard set-up. It hybridises easily with congeners, which has led to the production of many hybrids differing in colour and finnage.

Swordtail (Xiphophorus helleri)

This is ideal for the community tank as its water requirements overlap with most of the aquarium fish species. It’s best to avoid more than one male of these in the same tank, as they can be aggressive towards each other. Water should be neutral to slightly alkaline (pH 7.0–8.3).

Endler’s livebearer (Poecilia wingei)

This colourful species can be maintained in almost neutral to alkaline (pH 6.5-8.5) water of low to moderate hardness (5-25GH). Temperatures of 24-27°C/75-81°F are optimal and salt is not necessary.

Sailfin molly (Poecilia latipinna)

This species is found naturally in a wide range of habitats, ranging from pure freshwater to pure seawater. As such it is one of few that can be maintained in both after gradual acclimatisation. Salt is therefore not entirely necessary, but 5-30g per ten litres of water can be added if desired.

Guppy (Poecilia reticulata)

This is the most versatile species of livebearer, being able to tolerate a wide variety of water conditions, although wild guppies are found in clear

forest streams with slightly acid to neutral water.

Expert Q&A

Dr Heok Hee Ng answers some of your most frequently asked questions on livebearing toothcarps.

Does my livebearer need salt in the water?

This question has been long and often debated. The easiest way to answer would be to consider the natural habitats of the fish in the wild. That’s not easy for most species treated here, since they are now commercially bred.

Guppies, platies and Swordtails do not generally require salt as they tend to be found in pure freshwater habitats. Mollies may require salt as populations are known from brackish waters. However, most mollies have been raised in pure freshwater, so no salt would cause no great harm. Salt or not, when changing salinity of your aquarium do it gradually so that the fish have time to acclimatise.

How can I spot pregnant fish?

Pregnant females have a prominent gravid spot which is a dark area behind the anal fin. Although less noticeable, pregnant females also have a larger belly and a more squarish appearance, particularly when viewed from the front.

If I want to breed livebearers, what should be the sex ratio of the fish in my tank?

A ratio of one male to two or three females is ideal. Male livebearers are known to aggressively harass females to breed, so having more than one female to split the male’s attention is a good idea.

How soon can I expect fry?

Livebearers typically take about four to seven weeks to produce a brood.

What do I do if my female livebearer gives birth?

The first course of action is to separate the fry from females, as they are known to be cannibalistic and will eat their own young.

What do I feed livebearer fry?

Livebearer fry can be fed a variety of fry foods, although newly hatched brineshrimp are considered best. Commercial fry foods and crushed egg yolk can also be given.

How do I sex them?

Mature males are easily distinguished from females by the presence of a gonopodium — an inseminating organ modified from anal fin rays — sticking out of the anal fin. Males are also slimmer and tend to be the more colourful fish.

This item was first published in the September 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.