Sexing Guppies: Male Vs Female

how to sex guppies

Guppies are colourful, lively fish that are a popular addition to a home aquarium. They are easy to breed, but they will eat their young if given the chance. The male and female guppies have distinct differences that make them easy to tell apart once you know what to look for.

The male guppy is typically much more colourful than the female. His body may be splashed with many different colours, or he may just show one or two. The male’s tail and fins are usually long and flowing, especially in the fancy varieties. The female guppy is usually pale grey or silver, and her body is much rounder and larger than the male's.

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.

Characteristics Values
Body shape Males are long and slender; females are rounder and larger
Body size Males: 0.6-1.4 inches or 1-1/8 inches (3 cm); Females: 1.2-2.4 inches or 2-1/8 inches (6 cm)
Colour Males are more colourful and patterned; females are pale grey, silver, or brown
Gravid spot Present in females only, near the tail
Dorsal fin Males have long dorsal fins; females have short dorsal fins
Tail fin (caudal) Males have wide, long caudal fins; females have shorter caudal fins
Anal fin Males have long and pointed anal fins (gonopodium); females have short, triangular anal fins


Body shape and colouring

The body shape and colour of guppies are key indicators of their sex. Male guppies usually have slender, long bodies, while female guppies are rounder and larger, sometimes twice the size of a male. Male guppies are typically smaller, reaching about 0.6 to 1.4 inches in length, while females tend to be larger, measuring approximately 1.2 to 2.4 inches. This size difference is due to the female's reproductive role, as they carry eggs.

The colour patterns of male and female guppies also differ significantly. Males are known for their bright and vibrant colours, with dazzling patterns that make them visually spectacular. They use this colouring to attract females for breeding. On the other hand, female guppies have more subdued colours, usually muted greys or browns, and lack the striking patterns seen in males. This less flamboyant colouring helps protect them and their offspring by reducing visibility to potential predators.

While some female guppies may display a bit more colour, a comparison between males and females from the same spawn will reveal the greater vibrancy of the males. Additionally, male guppies often have orange, blue, violet, green, black, and white spots and stripes on their bodies and tails.

It is worth noting that the presence of bright colours and patterns on a guppy is not a definitive indicator of its sex, as some types of guppies have females that are also quite colourful. Therefore, it is recommended to consider other physical markers in conjunction with colouring when determining the sex of a guppy.

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Dorsal fin length

The dorsal fin is located on the top of the guppy's body, around two to three inches from the fish's head. Male guppies have longer dorsal fins that trail in the water as they swim. In contrast, female guppies have shorter dorsal fins that do not trail in the water as they swim. The difference is evident when the two guppies are moving in the water. Male guppies have flowing dorsal fins compared to their female counterparts. The females' dorsal fins do not trail or stream when they swim.

Male guppies have a long dorsal fin that flows in the water. The dorsal fins of male guppies are more prominent and elongated, sometimes featuring eye-catching patterns. The dorsal fin of a female guppy, on the other hand, is shorter and less extravagant. It does not hang in the water while they swim and is less noticeable.

The dorsal fin is one of the most noticeable differences between male and female guppies. Male guppies generally have longer fins than females, and these fins can also be more vibrant in colour.

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Gravid spot

The gravid spot is a dark area close to the anal fin of a female guppy, which is used to identify its sex. The spot gets darker and expands as the due date of giving birth to live fry approaches. The darker the spot, the sooner the female is about to give birth. Once the female guppy gives birth, the gravid spot becomes lighter. However, the cycle repeats when she is pregnant again.

The gravid spot is a certain way to determine the sex of a guppy since female guppies are almost always pregnant. They can store a male guppy's sperm for up to six months and will get pregnant every month without having to mate.

The presence of a gravid spot does not always indicate pregnancy. Female livebearers can have this spot, pregnant or not. The spot tends to get larger and darker during pregnancy, but this is not always the case. The expansion of the gravid spot can also be caused by the female developing a larger number of eggs.

The colour of the gravid spot depends on the colour of the female guppy. In females that are peachy/lighter in colour, the gravid spot will turn from pink to black when close to giving birth. In grey/darker females, the spot will change from black to pink.

The gravid spot is formed by the tearing of the peritoneum in the abdominal cavity underneath the fish's skin, exposing the egg/embryo sac and its pigments. The spot's colour intensity is linked to the developmental stage and clutch size, suggesting its reliable use as an external surrogate of key internal development in the species.

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Anal fin shape

The anal fin is located under the guppy and is the smaller fin right before the tail fin. The shape of the anal fin is a key difference between male and female guppies. Male guppies have an anal fin that is long and narrow, with a slightly pointed end. The female guppy, on the other hand, has a shorter anal fin that appears triangular in shape. The gravid spot, a marker of female guppies, is located right above her anal fin.

The male guppy uses his anal fin to deliver sperm into the female. The anal fin of the female guppy, on the other hand, supports her swimming and movement. The male's anal fin is modified and is known as a gonopodium, which acts as a copulatory organ. The gonopodium is long and pointed with several hooks on it.

The anal fin is a sure way to identify the sex of a guppy. The anal fin of the male guppy loses the triangular shape to make room for the gonopodium. The gonopodium is the male's reproductive organ, which may appear long and pointed or like a rolled tube. The female guppy's anal fin does not undergo any changes and retains its triangular shape.

The anal fin is one of the key differences between male and female guppies, along with size, shape, colour, tail length, dorsal fin shape, and the presence of a gravid spot.

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Behavioural differences

In one study, male guppies were found to be bolder than females when shoaling with the same sex. However, there was no difference in boldness between males and females when shoaling in a mixed-sex group. In this context, the social environment was found to have a significant effect on the boldness of both male and female guppies.

Another study found that male guppies were more persistent and less behaviourally flexible than females. Males made twice the number of errors as females when the reward contingency was reversed. This difference was not present during the initial colour discrimination learning phase.

In a simulated aerial predation attack, female guppies exhibited bolder behaviour when shoaling with males than with other females. Male guppies, on the other hand, exhibited reduced boldness when shoaling with females compared to males.

Overall, these findings suggest that male and female guppies exhibit different behaviours in various contexts, and that the social environment can have a significant influence on individual boldness.

Frequently asked questions

Male guppies are long and slender, while female guppies are rounder and larger. Males are also more colourful, with spotted or striped markings. Females have a dark spot on their underside, near the tail, called a gravid spot, which gets darker and bigger when they're pregnant.

It's nearly impossible to tell the sex of guppies when they're younger than one week old. After a week, female guppies will have developed their gravid spot, which can be seen with a magnifying glass and a flashlight.

If your guppy is pregnant, her body may look boxy, stuffed, or lumpy. Her gravid spot will get darker and bigger as she gets closer to delivering her young, and you may be able to see the babies inside her.

Guppies are known to eat their young, so you may want to separate them by sex.

The earliest you can accurately tell the difference between male and female guppies is one week after they're born. Before that, they're too small and underdeveloped to show any differences.

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