The Playful Platy


The Playful Platy
by Dr David Ford, Consultant to Aquarian®, member of Halifax AS

A Fun Fish

Only the Platy could be bred to have the face of Mickey Mouse and sell like hot cakes because of it! It is the dream fish for aquarists - pretty, active, peaceful, eats anything, accepts all waters, many varieties and easy to breed, what more can you ask of a tropical fish?

Even its name is funny. The original scientific name was Platypoecilius and so it became Platy for short. This was in all languages so the French, Germans, Spanish and others know the fish as the Platy too. When books such as German Fish Encyclopedia are translated into American English, US grammar rules are applied and the plural form makes the 'ys' become 'ies' - hence a shoal will be Platies. But British English grammar would make this 'plate-is' and the pronunciation is 'platt-is', so UK books use the (correct) term Platys, American books write Platies (indeed they call them 'colorful Platies').

Also, the fish is no longer Platypoecilius because the two different genera Platypoecilius and Xiphophorus (Swordtails) within the family Poeciliidae, were found to be scientifically the same (some can even crossbreed). Hence the Platy is now Xiphophorus too.

However, Xiphophorus means 'Sword Carrier' and aquarists say 'Why does the Platy have the same name as a Swordtail, when it has no sword?'. The reason is that when the Swordtail was first named, the Latin 'sword' was given not because of the tail sword, but because the male's gonopodium (the anal fin) was wielded like a sword during courtship! The Platy male certainly has one of these - and displays it too.

So Many Varieties

There are two species chosen for the aquarium trade: X. variatus (Latin for variable) and X. maculatus (Latin for speckled). Both species are very variable in both colour and patterning, hence cross-breeding the fish has led to many different strains, chosen for their potential sales by fish farmers and hobby breeders.

The fish can even be crossed with Swordtails giving hybrids that are sold under invented names such as the Sword Platy, Swordtail Platy and Marigold Platy.

Some of the colour strains of Platys to be found in the aquarium trade:

Red Platy Red Moon Platy Red Tuxedo Platy Red Wag Platy
Red Wagtail Platy Red-eyed Platy Red-tailed Platy Red Twinbar Platy

Black Platy Black Variatus Platy Black and Gold Platy
Black Banded Platy Black and Red Platy

Blue Platy Blue Variatus Platy Blue Mirror Platy

Gold Platy Gold Speckled Platy Gold Tuxedo Platy Gold Moon Platy
Gold Comet Platy Gold Crescent Platy

Yellow Platy Yellow Tail Platy White Ghost Platy Orange Spot Platy

The fish has popular names not based on the colour name too. One is the Wagtail Platy - this is a strain of X. maculatus that has black fins. The large tail fin is obviously 'wagging' as the fish dashes about the aquarium.

Another colour morph of X. maculatus is as yellow as the moon and is known as the Moon Platy. However, if the yellow is too orange, the fish becomes the Marigold Platy. If there is an iridescence present the fish then becomes the Coral Platy. There is even a Mirror Platy where the iridescence is pronounced.

There are also names that describe the fin shape such as the Hi-fin and Sword. Some strange fin shapes can be seen in Platy-Swordtail crosses known as Papagai and Spitz Platys (named after German and American breeders).

The Scientist's Fish

The fun fish has a dark side. The reason for the natural colour variation which breeders exploit, is in the genes. The species has a genetic form that gives different melanophores (the structures that contain colour pigments) in every individual fish. These are so dominant that they can run riot and become a melanoma (skin cancer). Cross breeding a Platy and a Swordtail that have strong black colours will often give a hybrid with an obvious melanoma, an effect well known to breeders…and scientists.

Hence the fish is used in cancer research, particularly because the fish can survive for years carrying the cancerous growth. Doctors need to know: how can it survive with such a disease?

The Nutritionist's Fish

Being hardy and a livebearer with anything from 10 to 75 vigorous fry born almost monthly, the fish is ideal for studies in fish nutrition. Hence the Waltham® Aquacenter had the specimens on feeding trials when Aquarian® was being developed.

From these trials I learnt that the fish needed 1/3rd of its diet as a vegetable and 2/3rd as animal origins. The fish is obviously an omnivore (can eat anything) but it is partly vegetarian; something is necessary from plants that the fish has to digest to be healthy. These will be phytochemicals - nutrients that derive from photosynthesis by plants in sunlight.

My Experience

The fish originates from central America, as far North as the USA-Mexican border (there is a 'Northern Platy'), through Guatemala, down to Nicaragua, all on the Eastern Seaboard, in ponds, swamps and calm rivers.

Hence, from this sheltered, but variable waters, the fish obviously enjoys the calm life of the aquarium. The fish I obtained however, were from Florida. Not wild species but the popular Wagtails bred en mass in Florida fish farms. I found they liked warm waters even though the books claim the fish will thrive in cool water (down to 12ºC). I used 25ºC, but 27ºC for breeding.

It is known the fish play in the sunlight in their natural home, so bright lights and floating plants (e.g. Najas) were included in 36x12x12" (90x30x30cm) tanks. The water was dechlorinated tapwater kept clear by gentle filtration (small powerfilters with foam). Shoals of a dozen Platys in each tank soon gave a constant supply of gravid females, obvious by their belly size.

These females were transferred (gently via glass cups, not netting) to individual 18"/45cm polytanks where they gave live births of immediately active fry. Each batch was raised on different recipes of crushed flake foods and rates of growth measured via photography.

It was in this research that the need for 1/3rd vegetable diet was discovered. Maximum growth occurred when the flake was supplemented with frozen Algae, blanched lettuce, squashed peas etc.

The fry grew rapidly and the males had to be removed within just 3 months when gonopodium development of the anal fin was seen. If left in the shoal, interbreeding started and the second generation fry were poor because of sisterxbrother genetics. Some books claim that the fish will not breed until about a year old - clearly this was wrong. Once the female was inseminated she would drop that same father's young many times too.

The Wild Ones

There are many wild Platys still living in Mexican rivers such as Rio Verde, Coy, Nautla and Atoyac - these range from cascading waterfalls to narrow jungle streams but all have quiet pools where populations of Xiphophorus species live out their lives.

Professional collectors and amateur breeders collect these fishes, ranging from Museum Zoologists to conservationists hoping to preserve endangered species. Even from the UK - the Viviparous Society have members who visit Mexico to help with collection and maintenance of sites.

With the constant supply of cheap fish from Florida, Hong Kong and Malaysian fish farms, it is rare to see the wild forms of Platys on sale in aquarium shops. But if you want to own a Central American River aquarium, the farmed fish look just as attractive and are as hardy as the wild species - and all are still Xiphophorus, the sword carriers.


Fry are produced regularly, of course, but these will not survive in the community aquarium. In a species tank planted with (American) bushy species (e.g. Myriophyllum, Cabomba, Egeria and Riccia) will give natural cover and food for the fry to survive.

Many Thanks to Dr David Ford,


Thanks to John without
his help I could not have made this site