From The Aquarium Wiki
The infamous Guppy, or Poecilia reticulata. Often sold as the beginners fish, it's known for its ability to multiply in number at a rapid rate. Suitable for tanks 37.9 Litres (10 US G.) or more, males usually stay under 5.1cm (2") in length, while females can be anything from 5.1cm (2") to 8.9cm (3.5"). As these fish are livebearers, it's best to keep them in the ratio of 1 male per 2-3 females to avoid the males harassing females to the point of exhaustion.
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