The Guppy, scientifically known as Poecilia reticulata, (a.k.a. the millionfish), is small, beautiful, peaceful, lively, curious and hardy – and one of the most popular freshwater aquarium fish species. It is a small member of the Poeciliidae family and like all other members of the family is live-bearing. It is also one of the best choices for beginners, especially children.

Guppies are native to Antigua and Barbuda, Barbados, Brazil, Guyana, the Netherlands Antilles, Trinidad and Tobago, the U.S. Virgin Islands and Venezuela. However, guppies have been introduced to many different countries on all continents, (except Antarctica), most often as a means of mosquito control, in the hope that the guppies would eat mosquito larvae, slowing the spread of malaria. But they were also introduced accidentally. In many cases, these guppies have had a negative impact on native fish faunas.

Today, however, to the delight of aquarists across the world, they are selectively bred to produce a variety of colours and patterns, as well as various tail forms, always with the aim to deliver consistency. Guppies exhibit sexual dimorphism – meaning that males differ markedly from females, to the point of sometimes being unrecognisable as the same species! In the wild females are grey in body colour, while males have splashes, spots, or stripes that can be any of a wide variety of colours. But breeders cross-bred the wild guppies that showed the most colours in each generation repeatedly, finally to produce the “fancy guppies” seen today. With today’s much more available information on genetics, this practice is still ongoing in a serious way.

Guppies prefer a hard water aquarium with a temperature between 25.5° and 27.8 °C and salt levels equivalent to one tablespoon per 19 litres. In fact, they can withstand levels of salinity up to 150% that of normal seawater. They are, however sensitive to temperature changes, especially dropping temperatures.

Guppies are omnivores and will eat most foods offered, however they need high quality vegetable matter such as Spirulina in their diet to thrive. A varied diet is  always best, and must include frozen or live foods such as Brine Shrimp, or Blood Worms.

Guppies are generally peaceful, though nipping behaviour is sometimes exhibited between male guppies, or towards other top swimmers like platys and swordtails, and occasionally other fish with prominent fins, such as angelfish.

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Of course, the Guppy’s most famous characteristic is its propensity for breeding; Guppies are highly prolific livebearers, which is why they are sometimes called ‘millionfish’! The gestation period of a guppy is 21–30 days, with an average of 28 days, varying according to water temperature. Males possess a modified tubular anal fin, the gonopodium, located directly behind the ventral fin, which is flexed forward and used as a delivery mechanism for one or more balls of spermatozoa. The male will approach a female and will flex his gonopodium forward before thrusting it into her and ejecting these sperm balls. After the female guppy is inseminated, dark areas near the anus, known as the gravid spot, will enlarge and darken. Just before birth, the eyes of fry may be seen through the translucent skin in this area of the female’s body. When birth occurs, individual offspring are dropped in sequence over the course of an hour or so.

For reproduction, Guppies prefer water temperatures of about 26 °C.  reproduction. The female guppy has drops of between 2 and 50 fry at a time, typically ranging between 5 and 30. Within only a few hours after giving birth, the female is ready for conception again . Guppies also have the ability to store sperm for up to a year, so the females can give birth many times without depending on the presence of a male.

From the moment of birth, the fry are fully capable of swimming, eating, and avoiding danger. If not kept separate, the older, mature guppies may eat the fry, so the use of a specially designed livebearer birthing tank, which can be suspended inside the aquarium, or a net breeder, or a separate 20–40 litre tank is recommended to protect and grow the fry. While this would never be the serious breeder’s choice, some hobbyists believe that well fed Guppies will not eat the fry and that well-planted tanks, offering a lot of barriers to adult guppies will shelter the young quite well. In this case, Java moss, duckweed (Lemna minor and other Lemna species), and water wisteria are all excellent choices. A continuous supply of live food, such as Daphnia, will also keep adult fish full and may spare the fry when they are born.

Young fry take roughly three or four months to reach maturity. In the aquarium, they are usually fed finely ground flake foods, baby brine shrimp or, unless they are put in a separate tank, uneaten food from the adults. In addition, they nibble on algae.

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