An Introduction to Livebearers
A livebearer is a type of fish that gives birth to live young rather than laying eggs like other fish. This is a very general term and so a lot of the fish in this group are unrelated. However, most of the livebearing species available to the fishkeeper are from the family Poeciliidae and originate from the Southern US, Central America, the Caribbean islands and the northern parts of South America. This article is in reference to those fish.
Before you decide to keep livebearers it is very important to consider how you will house the offspring which you will inevitably get.
Why keep livebearers?
There are several kinds of popular livebearer that are colourful, small, peaceful and easy to care for. This makes them ideal for the home aquarium. Since they breed so readily and the fry are easy to raise they make a perfect first breeding project.
Other types of livebearer such as the four-eyed fish (Anableps anableps) are kept because of their slightly odd appearance which can be appealing to more experienced aquarist who are looking for something a bit different.
Physiology of a Livebearer
The male impregnates the female by using a modified anal fin called a gonopodium. The fertilised eggs remain inside the female until they hatch and the live young are born as free-swimming miniature versions of their parents. Female livebearers can store the male?s sperm for a period of months and can have several broods even if they have mated just once. This means that even if you purchase only female fish you could still end up with fry.
Livebearers prefer to be kept in groups of at least 6 with at least 2 females to each male. This will prevent too much fighting amongst the males and will stop the females from being constantly harassed by the males.
Most livebearers can and will breed in your aquarium. There are a few options regarding what you can do with the fry. Firstly, you can leave them in the tank and the parents or other fish present will more than likely eat them. This will help cull the weaker fish but some people consider it a bit cruel. Alternatively you can place the pregnant female in a breeding trap so that the fry are safe and you can raise them in a separate tank. Then you have the option to either keep them if you have the space or give them to a local fish shop or a friend. You are unlikely to make any money from fry unless they are a rare species or strain.
Some popular livebearers
Guppy (Poecilia reticulata)
Guppies are one of the most popular aquarium fishes as they are easy to care for if kept under the right conditions. The males are more colourful and slightly smaller than the females. Fancy varieties are the most common type available since the wild type is fairly dull in colour.
Molly (Poecilia sphenops)
These fish have also been selectively bred into many different colour forms and different shapes such as sailfin and balloon. The wild form is a silvery grey colour but the most popular type in the aquarium trade is the black molly. Mollies can be aggressive towards other fish so care should be taken when choosing tank mates. It is often said that mollies are brackish fish and need salt added to the aquarium but this is unnecessary as they live in both freshwater and brackish environments in the wild.
Swordtail (Xiphophorus helleri)
Swordtails are named for the pointed extension on the males? caudal fin. They are larger than most available livebearers so are not suited to small aquaria. Again these have been selectively bred to produce many different colours and forms. The original wild form is an olive green colour with dark and iridescent stripes. This fish will interbreed with the platy if kept together.
Platy (Xiphophorus maculates)
Platys are available in many colour forms due to selective breeding. They are easy to care for and so are a great fish for beginners. These fish are closely related to swordtails and will interbreed if kept together.
Endler (Poecilia wingei)
This tiny fish came to the hobby in the 70s. There is still some debate over whether it is a variation of the guppy (Poecilia reticulata) which it is very similar to. It has been classified as a different species but it will interbreed with guppies if they are kept together so for this reason it is best to keep them separately. They prefer slightly warmer water than guppies and because of their small size are best kept in a species tank.