Guppies are popular pets and make attractive additions to a home aquarium. Male and female guppies will reproduce quickly once they mate, though guppies are known to eat their young. You can identify male and female guppies fairly easily once they are at least one week old. Compare their body colors and patterns.
Sexual harassment in the fish world—male guppies suffer most
How to Identify Male and Female Guppies: 7 Steps - wikiHow
We've seen in our simulations that the more brightly colored a male guppy is, the more likely he will be seen -- and eaten -- by a predator. In a simulation or in the wild, where predators are plentiful, male guppies become increasingly drab over generations, pushed by predation pressure toward greater camouflage. So if camouflage confers such an obvious survival benefit to prey species like guppies when it comes to predator avoidance, what possible advantage could there be to sporting colors and patterns that make an individual more conspicuous? The answer lies in the fact that guppies have to do more than just survive. They also have to reproduce -- and to do that, they have to attract mates. The "flashier" a male guppy is, the more likely a female guppy will choose him as a mate, giving him the opportunity to pass his genes along to the next generation.
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The guppy Poecilia reticulata , also known as millionfish and rainbow fish ,  is one of the world's most widely distributed tropical fish and one of the most popular freshwater aquarium fish species. It is a member of the family Poeciliidae and, like almost all American members of the family, is live-bearing. They are highly adaptable and thrive in many different environmental and ecological conditions. Wild guppies generally feed on a variety of food sources, including benthic algae and aquatic insect larvae.
Sex chromosomes regularly evolve suppressed recombination, distinguishing them from other chromosomes, and the reason for this has been debated for many years. It is now clear that non-recombining sex-linked regions have arisen in different ways in different organisms. A major hypothesis is that a sex-determining gene arises on a chromosome and that sexually antagonistic SA selection sometimes called intra-locus sexual conflict acting at a linked gene has led to the evolution of recombination suppression in the region, to reduce the frequency of low fitness recombinant genotypes produced. The sex chromosome system of the guppy Poecilia reticulata is often cited as supporting this hypothesis because SA selection has been demonstrated to act on male coloration in natural populations of this fish, and probably contributes to maintaining polymorphisms for the genetic factors involved.