The original Swordtail is green, but the most common culture form found is red. The swordtail is closely related to the platy and if they are kept in the same aquarium, they can cross breed very easily. In fact, most of the types that can be bought commercially are different cross breeds, but usually stabilized through many years of selective breeding to provide a particular type. It has helped to provide the many different cultural forms, such as the red swordtail, but also means that it is difficult to find a clean fish. Even if you find a green swordtail, there is no guarantee that it is "clean".
Looks
The males are easy to recognize, since they, in addition to the gonopodium, also has an extension of the lowest finrays in their tailfin. The extension looks a bit like a sword, which also explains the popular name, swordtail. The females are a little bigger than the males and could be mistaken for a very large platy. Apart from the males' sword and the size, it is only the body height that reveals if is a swordtail, since the swordtail is lower and the platy higher. It can be difficult to tell a low platy apart from a high swordtail.
Breeding
The swordtail female can get very big litters and even if you make no effort to save them, there are almost always some who survive. If you want to save more kids though, use a small dense aquarium of 16 to 54 liters, so the female will not get stressed. I do not recommend using a hang-on box for the female to give birth in as I think they are too small for the swordtail. The female give birth with a 4-6 week interval, so you can easyli get more fry than you have room for, especially if you have limited space for the purpose.
Status
I got mine in the start of January 2005, but very soon I remembered why I many years ago had abandoned my Swordtails - the males fight a lot and even the females are also quick to beat up on the weaker individuals. Therefore I rather quick decided to bye some indianer platies in stead and at the time I sold the Swordtails. Before I sold them, they got 2 batches of fry, which I decided to let grow out in my tanks. My experience was that it takes quite some time before the fry reaches a good size for sales, but it could also have been affected by the fact that I didn't have a large enough tank for them to grow in.
