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Poecilia sphenops, called the Mexican molly or simply the molly, is a species of poeciliid fish from Central America. It was once understood as a widespread species with numerous local variants ranging from Mexico to Venezuela, but these variants are today considered distinct species belonging to the P. sphenops complex and P. sphenops itself as being native to Mexico, Guatemala, and Honduras.
Amazon mollies have a small dorsal fin consisting of 10-12 soft rays. [9] The position of the dorsal fin on the back of the fish is anterior, closer towards the head, than the position of the anal fin on the underside of the fish. They do not have any spiny rays on their fins. [10]
Within a week or so, the fry begins to assume its final shape, although a year may pass before they develop a mature goldfish colour; until then they are a metallic brown like their wild ancestors. In their first weeks of life, the fry grow quickly—an adaptation born of the high risk of getting devoured by the adult goldfish. Carp
In birds and mammals altricial species are those whose newly hatched or born young are relatively immobile, lack hair or down, are not able to obtain food on their own, and must be cared for by adults; closed eyes are common, though not ubiquitous. Altricial young are born helpless and require care for a length of time.
Livebearers are fish that retain their eggs inside the body and give birth to live, free-swimming young. They are especially prized by aquarium owners. They are especially prized by aquarium owners. Among aquarium fish, livebearers are nearly all members of the family Poeciliidae and include: guppies , mollies , platies and swordtails .
All of these varieties exhibit signs of their pregnancy before the live fry are born. As examples, the female swordtail and guppy will both give birth to anywhere from 20 to 100 live young after a gestation period of four to six weeks, and mollies will produce a brood of 20 to 60 live young after a gestation of six to 10 weeks.
Sailfin mollies produce broods of 10–140 live young, depending on maturity and size, and females may store sperm long after the demise of their relatively short-lived mates. The gestation period for this species is about three to four weeks, depending upon temperature, and a single female may give birth on multiple occasions throughout the year.
They mature quickly and breed readily, with females giving birth to a dozen or more fry every month. [10] Some poecilids are cannibalistic and will eat any of their fry that are unable to flee in time (with females often eating the fry they just gave birth to, especially in a cramped aquarium setting).