Swordtail fish – Xiphophorus hellerii

Also known as Xiphophorus hellerii by its scientific name this fish species is spread in Central America from Guatemala to southern Mexico. The Swordtail fish is part of the popular family of Poeciliidae, live bearing fish, family which includes other popular species like guppy, molly and the platy fish.

Their original color is green, also called green swordtail fish, but after repeated selections in captivity more color variations had appeared: red xipho with black tails, red xipho with red eyes, albino xipho, simson xipho, black xipho or the xipho fish with veil like fins.The female can grow up to 12 centimeters in length but the male is usually smaller in size.

Sexual dimorphism is evident; the male will have the anal fin modified into a copulating organ and the caudal fin extended into a sword-shaped fin, therefore the name, “swordtail fish”. An interesting fact about this species is gender reversal, meaning at one point because of external factors like the pH a female can change into a fake male, developing a “sword” and the gonopodium (penis like organ for internal fertilizations), and this phenomenon can be reversible and therefore the fake male can turn back into a female and give birth again fry again.

In nature the Swordtail fish lives in slow moving waters with the water hardness between 10 and 15 dGH. Also, they prefer neutral or slightly alkaline waters within a tank of 80 liters or more, with good filtration and plenty of oxygen and plant life. They are active fish and relatively peaceful, can live in community tanks but usually will eat any young fish smaller then 1 centimeter. The males are somewhat aggressive, especially between themselves with one alpha male which will dominate over the food and females. It will eat both dry and live foods with no specific preferences.

As in most Poeciliidae breeding them is very easy. Just having some adult males and females together in a tanks means you most probably have pregnant females swimming around. You will need to separate the female in a well-filtered tank, 3-4 days before the estimated date of birth. After two or three births the female will average around 100 and 250 young per birth. After giving birth the female will need to be immediately removed from the tank as she will eat her young. Before reproducing such a fish make sure you will have the proper space and tools to raise the young, otherwise there is no point in starting such a venture. If you leave your females in community tanks, most of the times the young will get eaten right away, unless your aquarium is very big, giving the fry a lot of hiding places.