Wild Swordtails are found from southern Mexicoand down to Guatemalain Central America. They belong to the family Poeciliidae of the order Cyprinodontiformes, and they are closely related to ‘platy’ fish (X. maculatus), with whom they can interbreed. The name Swordtail is derived from the body of the male Swordtail. The bottom ray of his caudal fin is extended, and points out from the body like a sword. The female Swordtail has a fanned anal fin instead. She can also be distinguished from the male by her more rounded body shape.
Today aquarists can choose between red, black, green, albino and even neon coloured Swordtails, since Swordtails have been extensively bred in captivity. There are also many different Swordtail types, such as the Red Simpson, the Spotted Swordtail, the Gold tux Swordtail and the fanciful Lyretail.
IN THE AQUARIUM
You can keep one Swordtail in a 35 litre aquarium – at a pinch. However, the Swordtail is a very active swimmer and will do best in a larger aquarium. Keep in mind that for breeding purposes, the mating ratio should always be 1 male to 2-3 females; if you have only 1 female to 1 male, the male may chase her to death.
Swordtails are quite tolerant when it comes to water temperatures, and can live in temperatures from 18 to 27 degrees C. In the wild, the Swordtail lives in brackish waters. You can emulate this by adding marine salt to your aquarium. Naturally, the tank mates should then also be species content to live in brackish water. Keep the pH in the 6.8-7.8 range.
While considered community fish, Swordtails, especially the males can be aggressive, and they will often harass other fish, especially if they are kept in a cramped aquarium. You should thus carefully consider how to stock a swordfish aquarium. Also make sure your tank has a lid or a good hood, as sword tails are really good jumpers.
Swordtails are omnivores and will eat most foods offered with a leaning towards high quality vegetable matter such as Spirulina in their diet to thrive.
The Swordtail fish is a livebearer, so unlike many other fish species a female Swordtail will give birth to fry instead of depositing eggs. The male Swordtail fertilizes the eggs inside the female, and the eggs develop into fry inside her body. The gestation period is 28 days.
Just like with many other Livebearers, it is easy to get Swordtails into spawning condition. It is even possible for a female Swordtail reproduce in an aquarium without any male Swordtail present, since she can store enough sperm inside her body to fertilize six future batches. If your newly acquired female Swordtail unexpectedly gives birth without a partner, you will know that she has been kept with male Swordtails earlier and has saved sperm since then.
A common way of making the Swordtails breed in aquariums is to turn the water temperature up and keep it between 25 and 27 degrees C. The levels of soluble waste should be as low as possible, and you should also monitor the pH and make sure it stays in the ideal 6.8-7.8 range.
When the female develops a dark gravid spot , watch out for dark spots around her anus. When she looks as if her belly will explode any minute, you will know that she will soon give birth. These dark spots that you see around her anal region are actually the dark eyes of the fry showing through her scales. You can let her give birth in your large aquarium, but it is unlikely that fry will survive, because other fish will want to consume them. If you desire a high survival rate, you need to set up a special fry aquarium. Regardless of what you choose, the breeding aquarium should always be decorated with bushy plants, since Swordtails prefer to give birth in places where there are lots of hiding places for the fry. It is common for female Swordtails to give birth sitting at the bottom of the aquarium.
The fry will happily eat liquid fry food, newly hatched brine shrimp or flake food crushed into a fine powder. Their diet should also ideally include Spirulina algae. The combination of Spirulina and Brine shrimp is known to make the fry grow very rapidly, and this diet will usually make them show their true colours.