Guppies: Sexing And Breeding Basics

Guppies are a popular choice for home aquariums and are known for their ease of breeding. However, sexing guppies, particularly fry, can be challenging due to their small size and underdeveloped features. The earliest you can attempt to determine the sex of guppies is one week after they are born, once they have reached the adolescent stage.

One key difference between male and female guppies is their body shape. Male guppies typically have slender, long bodies, while females are rounder and larger, sometimes even twice the size of males. Female guppies may also appear boxy or stuffed if they are pregnant.

Another distinguishing factor is the presence of a gravid spot in female guppies. This is a dark area near the base of the tail, where the babies grow during pregnancy. While this spot can be challenging to spot in newborn fry, it becomes more apparent as the female matures.

Additionally, male guppies tend to exhibit brighter colours and patterns on their bodies and tails, which they use to attract mates. However, it is worth noting that some female guppies can also display colourful patterns, so this should not be the sole indicator of sex.

The dorsal fin, located on the top of the guppy's body, also varies between the sexes. Males have long dorsal fins that trail in the water, while female dorsal fins are noticeably shorter.

The anal fin, located under the guppy, is another indicator. Male anal fins are long and pointed, while female anal fins are shorter and triangular.

Guppy fry growth stages

Guppy fry undergo several growth stages before reaching adulthood, and proper care during these stages is crucial for their development. Here is an overview of the Guppy fry growth stages:

Newborn Stage

Right after birth, guppy fry scramble to find hiding places under gravel, live plants, or artificial plants. They are born with a strong instinct to seek shelter as they are often seen as prey by adult guppies and larger fish. Newborn guppies are about 0.6 cm in length and may appear slightly misshapen, but their bodies straighten within a few hours.

First Four Weeks

The first four weeks are critical for the development of guppy fry. They need good water quality, so weekly water changes are recommended. A sufficient food supply is also essential, with four to five small meals per day helping them grow faster. Lighting is another important factor, with 8-12 hours of light per day aiding their spine development.

Juvenile Stage

By the fourth week, guppy fry enter the juvenile stage, and their sex can be determined. Male guppies develop the gonopodium, while females exhibit the gravid spot near their anal tail. Males also start to display colours, with spots or streaks appearing on their bodies.

Young Adult Stage

Around the sixth week, guppies become sexually active. To prevent uncontrolled breeding, it is advisable to separate males and females at this stage. Guppies at this age should be fed a diet rich in protein and greens, with brine shrimp as their primary food source. Spirulina and plankton pellets can also be introduced to enhance their colouration.

Adult Stage

By six months of age, guppies are considered adults, although their growth rate slows down significantly. The fins and tails of male guppies may continue to elongate over time due to genetic factors. A well-balanced diet, rich in protein and low in fat, is essential for adult guppies to maintain their health and colouration.

Body shape

The body shape of male and female guppies is very different and distinctive. Male guppies usually have very slender, long bodies, while female guppies are rounder and larger than males, sometimes twice as big. Male guppies are typically slimmer with a streamlined shape that aids their fast and agile movements. They have a straight, torpedo-like body line that gives them an elegantly sleek appearance. In contrast, female guppies have a rounder and bulkier body shape. This is particularly noticeable when they are gravid or pregnant. The abdomen of a pregnant female guppy swells significantly, making it look considerably rounder compared to her male counterpart.

The difference in size between a male and female guppy is very apparent early on. Female guppies can grow up to 2 ⅛ inches (6 cm) and are often a lot larger than male guppies. Male guppies can grow up to 1-⅛ inches (3 cm). The bigger size of female guppies is largely due to their reproductive role of carrying eggs.

If your female guppy is pregnant, her body may look boxy or stuffed and even lumpy. She may grow even rounder as she gets closer to giving birth. When the fry are around 3 weeks old, you can determine their genders in an unusual way: by overfeeding them. When the female guppy gets fat, her belly will round out while the rest of her body remains trim. In the male, the chest area will swell instead, leaving the rest of the guppy streamlined. However, this method is impractical as it tends to create unhealthy fish and more waste to clean up.

Colour

Females, on the other hand, usually have pale grey or silver bodies. Some females do have a bit more colour, but if you compare males and females from the same spawn, the males will be much more colourful. The tail is the only part of the female that shows colour in adulthood.

Tails

Guppies are easy to breed, but it can be challenging to determine the gender of newborn guppies as they are tiny and still developing. The sex of the guppy can be confirmed by examining the tail, body shape, fins, and colouring.

The caudal fin, or tail fin, can help determine the sex of the guppy. Male guppies have wide, long caudal fins that are often brightly coloured, with elaborate patterns. Female guppies have shorter caudal fins that are not as wide and long as the males. Male guppies have longer dorsal fins that trail in the water as they swim, while female dorsal fins are very short.

Males have long and pointed anal fins, while female anal fins are triangular. The anal fin is the smaller fin right before the tail fin. The male uses his anal fin to deliver sperm to the female.

Male guppies tend to have more colourful tails and bodies, with bright colours and patterns such as orange, blue, violet, green, black, and white spots and stripes. They use this colouring to attract female mates. However, some types of guppies have females that are also quite colourful, so it is best to use other physical markers to determine the sex of your guppy in addition to colouring.

Anal fins

The anal fin is located under the guppy and is the smaller fin right before the tail fin. Both male and female guppies have anal fins, but they differ in shape and function.

The male guppy's anal fin is long and narrow, with a slightly pointed end. This fin is called the gonopodium, and it is the regenerative organ used to deliver sperm to the female during mating.

On the other hand, the female guppy's anal fin is shorter and appears triangular in shape. The gravid spot, a dark area near the abdomen and anal fin where the babies will grow when the female is pregnant, is located just above the female's anal fin.

In newborn guppies, the anal fins can be identical in appearance, so it is recommended to wait until the guppies are at least 2 to 3 weeks old before checking this feature as a means of sexing them.

Frequently asked questions