The Swordtail (Xiphophorous hellerii)

Xiphophorus hellerii (Xipho Cola d’Espasa/Swordtail). Bernat Arlandis, shot on May 23, 2013, CC BY-SA 2.0, via Flickr.

The Swordtail is one of the best-suited fishes for beginners. However, they are interesting enough to be relevant to the more experienced hobbyists as well. It is also perfect for community aquariums and all this is despite its stunning looks and ability to breed very easily.

Swordtails (Xiphophorous hellerii) are native to the brackish waters of South and Central America and were discovered in the mid 19th century. They have an elongated body with the males possessing an extension to the lower part of their tail fins which looks like a sword and hence the name. In the wild, they have an olive-green coloration with a red and yellow stripe running horizontally along the middle of their body. However, the Swordtails available in the aquarium trade are more intensely colored.

They are livebearers and that combined with their hardy nature made them one of the first fishes to be introduced in the hobby while also making them a great option for research purposes.


Male Marigold Swordtail. Eric Savage, shot on November 15, 2012, CC BY-SA 2.0, via Flickr.

There is quite a lot of variance when it comes to the coloration of Swordtails available in the hobby. Usually, they sport bright reds, yellows, and blacks bodies with different stripes and patterns on the more fancy varieties. While the “sword” on the tail fin is their most recognizable characteristic, some varieties do have long and flashy fins.

Some of the special color variants of this fish include Marigold Wag, Red Wag, Hi Fin Lyretail, Neon, Pineapple, and Painted. One thing worth remembering is that the fancier the variety, the more vulnerable they will be to diseases and other health problems as they are a product of generations of selective breeding and thus will require a higher level of care.

They are moderately-sized fish with the females tending to be larger than the males as they can reach a maximum size of a little over 6 inches or 15 centimeters while the males tend to stay south of 5.5 inches or 14 centimeters.

Tank Setup And Water conditions

Given their maximum size, they do need a slightly larger tank. They should be kept in a group of one male and three to four females and for such a group, the minimum recommended tank size is 30 gallons. If you plan to keep more fish then you will have to go for a larger tank. A larger tank also bodes well with its active nature. These fishes are also excellent jumpers. So make sure that the tank has a good lid.

As for the actual tank setup and décor, they do not really care about it all that much and it all depends on your creativity. The same applies to the substrate. Just make sure to leave plenty of open spaces especially towards the top.

Even though their natural habitat is among brackish waters, years of captive-breeding and their adaptability makes them perfectly suited to life in a freshwater tank. However, it can also be kept in a brackish tank as well. The important thing is to avoid any sudden changes.

The same applies to temperature and pH. They can tolerate a wide temperature range between 65°F and 85°F or 18°C and 30°C. They prefer alkaline water with a pH between 7.0 and 8.5 and hard water with a hardness of 12-30 dGH. They can also withstand minor fluctuations within these ranges but avoid anything too sudden or drastic.

The water needs to be properly filtered and aerated. Using a high-quality filter that provides enough surface agitation is highly advisable. Similarly, installing a decent heater is also a good idea to keep the temperature stable.


Their lifespan varies from three to five years but this can be considerably shorter depending on the specific variety as the fancy variants tend to live for around a year or two at most. The best bet to keeping them alive for a long time is by providing them with good food, maintaining stable water conditions, and being diligent with the maintenance.

Swordtails will readily accept all sorts of fish food. They can sustain themselves equally well on commercial fish food in the form of pellets or flakes just as they would with live, frozen, or dried food. A mixture of both is the ideal way to go.


Swordtail fry at 1 day old. Ltshears, CC BY 3.0, via Wikimedia Commons.

The Swordtail is one of the easiest fishes to breed. In fact, you do not really need to do anything special to get them to breed. They will do that all on their own without any special intervention as long as there are about four females for every male. They are livebearers which means that they give birth directly to their young. However, if you want most of the fry to survive then separate them from the adults as soon as they are born. Providing plenty of hiding spots can also work but to a lesser degree.

One thing to keep in mind is that if no new Swordtails are introduced, each subsequent generation will turn out to be weaker due to inbreeding. To avoid this introduce new Swordtails every now and then while swapping out the older fish.

It is also worth mentioning at this point that they can sometimes breed far too easily and far too often and this can lead to a population explosion. Be ready for that when getting these fish.


A swordtail and Molly in an aquarium.
Swordtail and Molly. Kai Schreiber, CC BY-SA 2.0, via Flickr.

Swordtails are generally docile fish. However, the males can become territorial and show signs of aggression especially if there are no hiding spots and there aren’t enough females. Providing hiding spots and keeping the 4:1 ratio will help avoid any aggression for a sustained period. If you have a smaller tank then keep only a single male.

They can be kept as a part of a community aquarium as well. However, the caveats are similar. The tank needs to be large enough to give each fish plenty of space and there should be multiple hiding spots. In addition to this, the tankmates need to be similarly docile. Swordtails will occasionally pester smaller fish but as long as those fishes are in a group of their own, it won’t be much of an issue.

Great tankmates for the Swordtail include

  • Platies
  • Mollies
  • Coolie Loach
  • Corydoras Catfish
  • Angelfish
  • Tetras as long as they are in a group


Despite how easy it is to keep the Swordtail and how readily available they are, there is something about these fishes that make them special to aquariums hobbyists with varying degrees of experience. Beginners will absolutely love them due to their hassle-free nature. They are also more forgiving of beginner mistakes than most fish out there.

However, their looks and interesting habits make them a great option for the more experienced hobbyist as well who is looking to expand his or her repertoire with something that is much less demanding but can still lend itself to create a stunning aquascape thanks to their brilliant coloration.

 The ease with which they breed can either be a pro or a con depending on your personal taste but there is no denying the fact that these fish act as great learning tools.

At the end of the day, there are a few fishes that were instrumental in the establishment of the aquarium hobby itself and the Swordtail is one of them and for that reason alone, every hobbyist should keep them at least once.

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