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Matt Clarke looks at the Platy - a common and easy to keep livebearer that often gives birth in the community tank.

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Common name: Platy, Southern platyfish
Scientific name: Xiphophorus maculatus
Origin: The Platies sold in the shops are always commercially bred. The original wild fish came from Mexico and Belize.
Size: Females can reach around 8cm/3", but usually 6cm/2" is the norm for this species.
Diet: Platies will accept most foods, ranging from flakes and granules, to frozen foods such as bloodworm and daphnia.
Water: Prefers slightly alkaline water, but is generally unfussy and hardy. Aim for a pH of 7.0-8.0 and a hardness of 3%20GH°C. Temperature can be anywhere from 24-28°C.
Aquarium: Platies are a very easy fish to keep and are ideal for the newcomer to fishkeeping. They mix well with most community fish and have few bad habits (with the exception of being prolific breeders). You'll need a tank of at least 60cm/24" to do these fish justice, and they are best kept in a group.

If you want to breed them, keep a single male alongside four or five females and plant the aquarium with bushy plants such as Water wisteria or Cabomba, so the fry have somewhere to hide. Avoid the temptation to buy a breeding trap. Platies are too big for these, in my opinion, and often get stressed. Get a separate aquarium and put the female in that, if you think she needs to be removed from the main aquarium.

If you don't want to breed them, don't buy any females. Platies can store packets of sperm, called spermatozeugmata, in the folds of their uterus and can fertilise several batches of eggs from a single spawning. As a result, that single female platy you purchase could go on to give birth to several batches of fry, each containing 20-50 offspring.
Breeding: Incredibly easy - there is no skill involved in getting these fish to spawn and they will do so even when conditions are a bit ropey. Platies give birth to fully-formed live young, rather than scattering or depositing eggs, and the offspring may survive to maturity in the aquarium.
Sexing: Males are smaller than females when adult and have a distinctive anal fin common to many livebearing fishes in the Poeciliidae family. This "gonopodium" is used for internally fertilising the female.
Similar species: Almost all platies on sale in the shops, with the exception of rare varieties sold from captive breeding programmes, will be commercially produced fish. Only two species are commonly sold, X. maculatus, and the related Variatus platy, X. variatus. The latter tends not to come in as many colour varieties and tolerates much lower water temperatures (down to 16°C) due to the climate in which it is found in nature.
Availability: Dozens of different varieties are available, all of which are selectively bred varieties of the same fish. Platies are one of the most widely sold aquarium fish and you can buy several different strains at most decent shops.
Price: Expect to pay around £1.00 for the most common varieties, such as Red or Red wagtail platies, but up to a few pounds for the more exotic strains, such as Pintails or Hi-fin platies.

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