The Swordtail

The Swordtail (Xiphophorus hellerii)

Order Cyprinodontiformes , Family Poecilidae

Common names
Swordtail

Synonyms
Poecilia hellerii, Xiphophorus hellerii hellerii, Xiphophorus helleri, Xiphophorus guentheri, Xiphophorus jalapae, Xiphophorus brevis, Xiphophorus strigatus

Description
Although the swordtails commonly seen in shops are usually Xiphophorus hellerii, there are several other related species which also go under this common name. The reason is plain to see; the males of these species all have a characteristic elongation of the lower part of the tail into a long ‘sword’. The Xiphophorus hellerii, common, swordtails in aquarium shops are the easiest to keep, and the most attractive for most fish keepers. While other species are usually kept by enthusiasts of wild form fishes, the aquarium swordtails have been bred to show a striking range of colours. Red, green, black, yellow and combinations of these colours provide a range of fishes which should suit everyone’s taste.

Behaviour
These are usually placid and peaceful fishes, although sometimes male swordtails can become aggressive to one another. It is best to keep either one male with two or more females, or a large enough group that there is not one individual who is constantly victimised. It is unusual for swordtails to cause trouble for other fishes, and they are good community fishes.

Aquarium requirements
As the swordtail grows larger than its popular relative the platy, they do require a correspondingly bigger aquarium with lots of swimming space. Females can reach up to four and a half inches, although the males are slightly smaller, so if a group are to be kept a large tank is required. Like many livebearers, they prefer hard, alkaline water; indeed have been naturally found in brackish waters. In the wild they are found in fast flowing Central American waters, and enjoy a good current in the aquarium. Although the tank should be well planted, they do need to have a good area of swimming space.

Feeding
These fish are easy to please in the aquarium. Surface feeders, they enjoy flake food, but will appreciate live foods too. They will nibble at algae in the aquarium, but will do best with foods with a high proportion of meat.

Breeding
Swordtails are livebearers, who give birth to up to eighty fry which are born free-swimming. The male can be differentiated from the female by his anal fin, which is modified into a long thin spike, the gonopodium. This specially modified fin is used to insert the sperm into the female. As swordtails will often eat the fry as they are born, lots of plants, especially floating ones, will give the tiny fish a chance to escape their parents depredations. The spawning traps sold in many aquarium shops are far too small for a full-size female swordtail, and cause a high degree of stress. Ideally the female can be moved, while still relatively slim, to a heavily planted spawning aquarium where she can give birth in peace, and be removed as soon as she has finished leaving the fry to grow. To grow them to full size requires a lot of space, so you will probably need to give away some of the fry to allow the others room to grow.

Diseases and disorders
Swordtails are hardy and resilient fish, which are not prone to any particular diseases, although in softer water or bad conditions they can occasionally suffer from white spot or fungus. Either of these is easily treatable with remedies from the aquarium shop, and should serve as a warning sign to increase cleanliness and check water conditions more often.

Notes
The swordtail is a striking fish, which has much to recommend it to beginners and experienced aquarists alike. The range of colours (and the possibility of breeding new strains), its resilience, and the ease with which it can be spawned and reared make it a fish which is guaranteed to be a favourite of many aquarists.

This article has been kindly provided by Kathy Jinkings and cannot be reproduced without her permission.

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