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Xiphophorus hellerii - Swordtail


  • Xiphophorus hellerii - Swordtail

    Photo thanks to globali

    Scientific name: Xiphophorus hellerii
    Common name: Swordtail
    AKA: Green swordtail
    Mistakenly or previously labelled: X. helleri

    Country of origin: Central & North America

    pH: 7.0 – 8.0
    Temperature: 20 - 28c
    Hardness: 10 – 30 dGH
    Water flow: standard
    Oxygenation: high

    Maximum size: 14 cm – male; 16 cm - female

    Diet: Live, frozen, flake & pellet foods – an omnivore.

    They will eat algae, including green hair algae.

    Males: Smaller, modified (long & pointed) lower lobe of the caudal fin “sword” tail, modified (pointed) anal fin (AKA gonopodium)
    Females: Larger, standard caudal fin, standard anal fin

    They are livebearers, breading readily and prolifically. The females are capable of mating once in a lifetime, then storing the sperm to be used every time they spawn (about once every 4 – 7 weeks).

    They will not usually eat their own and each other’s fry, so the population can quickly overrun even a medium sized tank, so plans should be made for disposing ethically of the offspring (e.g. taking them to a willing Local Fish Store).

    If there is a mature male in the tank, the females will develop to sexual maturity more quickly, while it will slow the maturation of juvenile males in the tank.

    To ensure the fry survive, provide floating and dense vegetation.

    They are able to interbreed with other platy species, so only one platy species should be kept per tank.

    Lifespan: 3 - 5 years

    Tank companions:
    They are NOT good tank companions with shrimps.

    They are a schooling species. They should be kept in groups of 6+, with at least 4 females per male, as the males will chase and harass them constantly.

    They are fast-swimming and boisterous with other tankmates, far more so than other platys or any of the molly species. They are suitable to live with mollies, but should not be kept with other platies, as they can interbreed.

    As with any fish they will eat any fish small enough to fit in their mouths, and equally can be eaten by any fish large enough to eat them. This should be taken into account when choosing tankmates.

    Stocking plans can be checked with

    Minimum tank size is 3 ft for a small group. More room is needed for a larger group and/or tankmates. Bear in mind when planning your tank size and stocking levels, that they are prolific and frequent breeders. If you do not want them to breed, buy males only.

    They could be kept in a heavily planted tank with floating plants to subdue the lighting and open areas for swimming.

    They excrete a lot of waste for their size, so will need adequate filtration (more than other fish their size) and frequent large water changes.

    They require hard, alkaline water and will not cope with soft, acidic water (they will become sick & die).

    They do best in brackish, rather than fresh water and can be found naturally in both brackish and marine environments. They are commonly used to cycle marine tanks. Although they can be transferred into more salty conditions fairly rapidly, they should be acclimatised back to fresher water very slowly, as it will put more pressure on their kidneys.

    Confused with:
    There are other recognised species in the genus known as mollies, all of which are allowable imports to Australia:
    Xiphophorus hellerii - Swordtail
    Xiphophorus maculatus – Platy – shorter body, lower dorsal fin
    Xiphophorus variatus - Variegated Platy – longer body, longer dorsal fin

    There are colour morphs & variations in form, some of which are crosses with X. maculatus or X. variatus, including, but not limited to:
    Green – wild form

    There are introduced (feral) populations in many countries.

    Wild fish are very rare in the trade, with the majority being commercially bred. The extent of this breeding has made a previously very hardy fish more prone to disease, but they are still an excellent choice for beginners.

    Xiphophorus hellerii are legal imports to Australia as of 12/11/2013 (list last updated 16/10/13).

    The IUCN Red List reports Xiphophorus hellerii as a species which has not yet been assessed, at 25/01/2013:

    It is very important not to release any aquarium specimens into our waterways. Any that are not sold or re-homed/ given away, can often be re-sold to aquarium stores. If they are homed in ponds, care should be taken that they cannot escape in run-off into our waterways. Even if fish are native & local they should not be moved from one waterway to another, as this can transfer disease. If they are not local fish, they can both spread disease and either out-compete or eat local fish, shrimp & plants, causing their demise.

    They are good fish for beginners.

    Relevant threads:

    Beginner’s fish & they poop a lot:

    Underrated/ fry:

    Don’t keep with shrimp:

    Eat algae:

    Feral in QLD waterways:



    Seriously Fish:


    WA Museum – feral populations established in Australia:

    Pics & threads with pics:

    Green – wild type


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