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How to Tell a Male From a Girl Guppy

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It’s easy to become captivated by the colorful, lively little guppy, a pleasant and attractive addition to almost any freshwater aquarium. Guppies give birth to live young and reproduce quickly and easily, though they will devour their young if given the chance. The males and females have distinct differences that make them easy to tell apart once you know what to look for.

Fins and Color

The male guppy is typically much more colorful than the female. His body may be splashed with many different colors, or he may just show one or two. Regardless, he’s typically brightly colored and definitely attracts attention. The male’s tail and fins are usually long and flowing, especially in the fancy varieties. Looking at color only is not entirely a reliable guide, though, since in some types of guppies the females may be quite colorful and have longer tails than the females of other species. In this case, it helps to look at some of their other characteristics to determine gender.

Overall Body Shape

Male and female guppies have very different body types that become quite obvious as the fish mature. Males are smaller overall, and their bodies are long and thin. Females grow much bigger than the males, and they have much heavier-looking bodies. The female’s body is much more rounded compared with the male’s. If she’s pregnant, her body may look stuffed, boxy or very full, perhaps even a bit lumpy, as she nears the time for her young to be born.

The Male’s Special Equipment

As a male guppy begins to mature from a fry into an adult, his anal fin, located under his belly, begins to undergo some changes. Over time, this fin slowly loses its triangular shape, becoming long and narrow until it eventually develops into a gonopodium. The fish is able to control the movement of this special fin and uses it to deliver sperm to the female. Once he’s done the job, she can deliver litters of fry, roughly once a month for up to seven months, without seeing a male again.

The Gravid Spot

One of the most obvious characteristics of a female guppy is her gravid spot. This is a dark spot located on the underside of her body near her tail. If she’s pregnant, a female’s gravid spot will get darker and bigger as her delivery date approaches. When the time is very near, it’s sometimes possible to see the babies within. Once her babies are born, the spot gets immediately lighter but will darken again as she broods another batch of youngsters.