Poeciliidae family - Livebearers
At the beginning, the Livebearers family fish used to live only in America, but because they are mosquito larva eaters they were introduced in other countries too in order to eradicate the population of mosquito. They live near the surface of calm waters or lakes and feed with insects, larva and vegetal supplement. There are differences at reproduction level, males and females differ as both body size and caudal and anal fins aspect. They are viviparous fish, because the females give birth to living fry. The male`s anal fin, transformed into a gonopodium (reproduction organ). The 3rd, 4th and 5th rays of the anal fin are prolonged into a tube through which the spermatozoids will get into the female genital system. This change takes place during the sexual grow. The fry don`t have a gonopodium and while they grow their entire anal fin, genital area, anus and abdominal fins move forward to abdominal or pectoral area. Using specialized muscles, the gonopodium can be rotated with 220°. The spermatozoids are kept into packs delimitated by a specialized membrane. While the reproduction act, the male introduces the gonopodium apex into the female`s genital area and releases a pack of spermatozoids. For a period of time it was thought that the male releases the spermatozoids in the water, near the female`s genital area, but due to research it was discovered that the fecundation is internal not external. The membrane of the spermatozoids pack dissolves releasing the spermatozoids into the female`s ovaries. The eggs are fertilized internal, but a part of the spermatozoids is kept for further fecundations. That`s why a female can give 5-7 births without another mating. The eggs have a big vitally sack permitting the evolution of the embryo inside the egg. For the species with small vitally sack, the embryo receives supplements from the female. A pregnant female is easy to be recognized because she has a big black spot in the anal area, it`s the genital spot. There is a Poeciliidae specie which has only females, Poecilia formosa, the males are unknown. These females mate with other species males, their spermatozoids fecundate the eggs and die, the characters of the species don`t get mixed. After birth, the fry is big enough to swim free and start feeding. Their first act after birth is to reach the surface of the water in order to full their swimming vesicle. The gestation period is between 4 and 6 weeks depending on the specie, and the female can be stimulated with fresh water adds. The pH has to be over 7. In soft andht acid water these species of fish are sensitive to diseases. In an aquarium with more than 1 male, they fight and one of them becomes the dominant male. In the aquarium water we have to add from 1 to 4 spoons of salt, depending on the specie. Some of the Poeciliidae species also need vegetal food.