Livebearers

Liverbearers

In live-bearing fish the eggs are fertilized internally in the female. In mating the male transmits the spermotozoa (In the form of a sperm packet) using a mating organ called the gonopodium which has developed from the anal fin. The eggs develop inside the mother and are born as free-swimming fry.

Advatages of bearing live young:

Eggs and young are protected from all predators to small to attack the mother herself.
Young wont die in bad conditions as long as the mother survives.
A single pregnant female can establish a new population in an unpopulated environment.
In many livebearing fish one mating is sufficient for several broods, since the sperm can be stored in the female's body.