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Live Bearing Fish

There are animals in most of the classes of vertebrates that have their babies alive rather than laying eggs.  One important class in which all species lay eggs is the birds.  In mammals, reptiles, fish and amphibians they are examples of both egg laying and of live bearing species.

There are a lot of types of live bearing fish, including the Whale Shark and the Great White Shark.  However, this article is mainly about just one group, the live bearing tooth carps.  This group includes many popular aquarium fish such as the Guppy, Platy, Swordtail, Molly and Endlers Guppy.

The males of these fish have a modified anal fin that is used to transfer packets of sperm to the female.  Generally, the female can store enough sperm from one mating for several lots of babies.  A female will often have stored sperm from several males and have babies with different fathers in one litter.  In most species of these fish, the female chooses which male she allows to mate with her, and her choice of male is one of the factors that have led to colourful males.

The eggs are produced inside the mother, and have good stores of yolk.  They are retained in the mother until they are ready to hatch.  Many mother fish are potential cannibals and their babies need to find safety as soon as possible after birth.  The babies of this group tend to be big in relation to the size of their parents and to be well developed at birth. 

This group of fish is native to the warmer parts of the two American continents, but have been introduced into every continent except Antarctica.  In some paces they have caused enormous environmental destruction to the native ecosystems.