Swordtails
The sword is an extension of the male's tail fin and grows with him. Livebearers, active, and they will jump a tank that has no lid.
Overview
Swordtails are livebearers from the rivers of Veracruz down to northwestern Honduras, and they are larger than most people expect from the same shelf as guppies and platies. FishBase records males to 14 cm including the sword and females to 16 cm.
The sword itself is an extension of the lower lobe of the male's tail, it carries no function in swimming, and it is what a female is choosing on. Everything else about the fish is a robust, active, undemanding community animal.
Temperament
Lively and peaceful with other species, and not always peaceful with each other. FishBase notes that males are aggressive towards one another, so one male in a group of females is the arrangement that stays calm.
They are strong swimmers and use the full length of a tank rather than a corner of it. Females produce 20 to 200 young after a gestation of 24 to 30 days and mature at eight to twelve months, which is slower than a guppy and makes the population easier to keep on top of.
Care and grooming
Worms, crustaceans, insects and plant matter in the wild, so a flake with vegetable content, plus frozen food and blanched greens.
FishBase gives 22 to 28 degrees C, which is 72 to 82 F, pH 7.0 to 8.0 and moderately hard water. They are as tolerant as any tropical fish sold, and the main thing that shortens a swordtail's life is a tank too small for a fish that swims as much as this one does.
Living and exercise
An 80 cm tank, about 30 gallons, which is a step up from what platies and guppies need and is set by the fish's own size and activity.
A lid is worth having. Open water through the middle, planting at the ends, and a group with a single male keeps the tank settled. They mix well with tetras, corydoras and other peaceful community fish of a similar size.
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