Poecilia reticulata, or the guppy, is easily identified by its distinct sexual dimorphism, where smaller males exhibit vibrant and diverse coloration with a rod-shaped gonopodium and often elaborate fins, while larger females are typically a uniform silver-grey with a fan-shaped anal fin and may develop a gravid spot when pregnant; males display a wide array of colors and patterns across their bodies and fins, which vary significantly in shape and size, contrasting with the females’ more subdued appearance, although ornamental strains may show some fin coloration; these livebearing fish have an elongated body shape, with males generally ranging from 1.5 to 3.5 cm and females from 4 to 6 cm, making their visual differences a key identifying trait.