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The Swordtail – Xiphophorus


Red Swordtail

The Swordtail is probably one of the most elegant of livebearers.

The Swordtail is a peaceful, elegant and, as a mature adult, large fish amongst livebearers and the elegant tail of the male fish sets it apart from the crowd.

Origins of the Swordtail

The Swordtail is native to Mexico and to northern Central America. At the time of writing it is considered to be an endangered species south of Mexico.

There are around 28 species of the Swordtail and the species can tolerate, to a certain extent, brackish water but not to the extent that a Guppy or Molly is capable.

Some of the species are hybrids, due to cross-breeding with Platys, a significantly smaller livebearer without the distinctive sword on the lower part of the male caudal fin.

Characteristics of the Swordtail

An adult female Swordtail will grow to over six inches in length. The Swordtail is an ideal aquarium fish, as it is a very peaceful fish both as a single species and with other species.

You will see from the location of its mouth that it is a top-feeder.

As is common amongst livebearers, the male fish has the adapted anal fin (the gonopodium) for mating with the female whilst (again, typical amongst livebearers) the female has a significantly larger body.

The male Swordtail sports the long, elegant sword on the lower section of the caudal fin which, in an ideal specimen, is outlined in black, starting from just behind the gonopodium and is almost equal in length to the length of the body of the fish.

Due to hybridization, many fishes purporting to by Swordtails are likely to be a mix of Swordtail and Platy though this may not become apparent in younger fishes, as the caudal fin develops as the fish grows. The hybrid males generally have far shorter “swords” than the purebred Swordtail and it seems far easier to purchase a hybrid than a purebred Swordtail.

The male Swordtail can grow to around 5.5″ whilst the female Swordtail can grow to more than 6″. The adult Swordtail in the wild enjoys faster-flowing water though younger Swordtails prefer less vigorous waters. Due to the size of the adult Swordtail a tank of at least 36″ in length is recommended.

Feeding the Swordtail

Being omnivorous, the Swordtail will accept flaked food, daphnia, bloodworm, tubifex worms as well as brine shrimp and, as always, it is better to provide sufficient food for your fishes to consume in two to three minutes once per day.

Swordtails will browse off your plants therefore if this browsing becomes detrimental to your plants then you may wish to feed them twice daily. Some aquarists feed their Swordtails three times daily.

The Swordtail – Video

Breeding the Swordtail

A typical brood of Swordtail can number up to around 100 and of these, around 70% are likely to be female. This is quite typical amongst livebearers and is also an indication that for each male Swordtail you should have at least two female Swordtails, preferably three, possibly four in my experience.

As with all livebearers, the male Swordtail is ever-eager to mate so having two or three females for each male gives the female some respite from the constant attentions of the male.

By choice, the female Swordtail tends to choose to mate with larger male Swordtails but, unlike Mollies, for example, the female may make her selection based upon colouring, markings, may select a longer or shorter “sword” or some other preference but, as is the way with livebearers, the male Swordtail is ever-eager to mate and will dispense with the mating ritual if his advances are unwelcome and simply launch a surreptitious mating if he can catch the female unawares.

The female is also able to store the sperm packages from males for several months so, in the absence of males, the female can use that stored sperm to fertilize batches of eggs. The female can also simultaneously bear the young of different males (polyandry).

The breeding cycle is around 40 to 50 days so you can anticipate the addition of 100 fry around eight times per year.

The Swordtail and Platy will interbreed so if you wish to ensure that you maintain your Swordtails in the pure form them it is advised that the two species are not kept in the same tank.

Male Swordtails, whilst in breeding mode, can become aggressive particularly towards their intended mate.

Interaction with other species

In the wild, Swordtails are not shoaling fishes but are generally good community fishes in the aquarium.

Larger or aggressive fishes (such as some Cichlids) have been known to target Swordtails (particularly male Swordtails). Two such culprits cited are the Convict Cichlid and the Jack Dempsey Cichlid.

As stated in the section on breeding, Swordtails will interbreed with Platys so it is advised that if you have a pure strain of Swordtail then don’t include Platys of either sex in the same aquarium.

Susceptibilities of the species

The Swordtail, like most livebearers, is a hardy species so is likely not to be susceptible to disease or to predation (excepting from certain Cichlids).

As with all fishes, always keep a close eye out for White Spot (“Ich” or “Ick”) and, in Swordtails there can be a susceptibility to Cottonmouth.

Varieties of Swordtail

The Swordtail found in the wild is the Green Swordtail.

Green Swordtail
Green Swordtail

The Montezuma Swordtail is reputed to have the longest “sword” amongst male Swordtails and note its fan-like dorsal fin.

Montezuma Swordtail
Montezuma Swordtail

Other Swordtails include:

  • Chiapas Swordtail
  • Sheepshead Swordtail
  • Yellow Swordtail
  • Delicate Swordtail
  • Highland Swordtail
  • Mountain Swordtail
  • Southern Mountain Swordtail
  • Panuco Swordtail

Mike Wheeler

I started keeping freshwater tropical fish in 1972 and it has been something of a passion ever since. In this website, my aim is to build up an everyman's guide to help the everyday aquarist get the best from this inspiring and entertaining hobby.

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