What to Know About Swordtails

Medically Reviewed by Vanesa Farmer, DVM on January 09, 2023
5 min read

The swordtail is a beginner-friendly tropical fish species. This hardy fish comes in various vibrant colors and can be kept in a freshwater tank as small as 10 gallons. These traits make swordtails popular pets for many hobbyists and fish breeders. If you’re considering getting a swordtail, there are a few care requirements to keep in mind. Here’s everything you need to know about swordtail characteristics, diet, breeding, and more. 

The swordtail (Xiphophorus hellerii) is a live-bearing freshwater fish. Its name comes from the male’s long, straight lower tail lobe, which resembles a pointed sword. The female has a rounded tail fin. 

This fish has a triangular head and conical upper and lower jaws. The male has a somewhat elongated body, while the female typically has a plumper abdomen. The male has a large, sail-like dorsal fin that it raises to intimidate potential competitors during courtship rituals. 

The common green swordtail has a brown or red midlateral stripe that extends from the head to the tail. Some fish have two reddish stripes above and below the midlateral band. 

The swordtail is known for its adaptability and resilience. It has a tenacious temperament and can hold its own when kept in community tanks with larger fish species. Male swordtails may become aggressive toward each other. Experts recommend keeping a ratio of three females to one male to help keep the peace. 

The average swordtail fish lifespan is 3 to 5 years.

Ornamental fish breeders have developed over 50 unique strains of swordtail that come in a rainbow of colors and patterns. Some varieties also have caudal and dorsal fin modifications. Here are a few varieties that you may find at your local pet store or available through an ornamental fish distributor:  

  • Black lyretail
  • Calico lyretail 
  • Green wagtail
  • Golden comet
  • Golden hi-fin
  • Marble
  • Lemon
  • Neon wagtail
  • Pineapple hi-fin 
  • Red velvet 
  • Tuxedo lyretail 

The red varieties are especially popular with aquarium hobbyists because of their striking color.

Hybrid swordtails can make beautiful and unique pets, but they may also be more prone to health problems due to hybrid incompatibilities. One recent study discovered that male highland-sheepshead swordtail hybrids are more likely to develop malignant melanoma on their tails. This melanoma damages the tail fin and decreases survival in the wild.

The swordtail fish originates in tropical freshwater ecosystems in Central America. The species’ natural range stretches from Veracruz, Mexico, to Northwestern Honduras. Wild swordtails live in swift-running rivers and streams with plentiful vegetation. They also inhabit ditches, ponds, and warm springs. 

This adaptable and hardy species has been introduced to nonnative habitats in at least 31 countries, including:   

  • Australia 
  • Austria
  • China
  • Hong Kong 
  • Indonesia
  • Madagascar
  • New Zealand 
  • U.S.

The species was likely introduced to these environments by pet owners who released their pets into the wild. Swordtails may also escape from fish farms. These fish can harm native fauna when they enter new ecosystems. For example, swordtails that invaded a thermal spring in Wyoming may have caused the decline of the Utah sucker (Catostomus ardens). Similarly, investigators identified swordtails as a possible cause of shrinking populations of native damselflies in Oahu, Hawaii. 

Aquarium owners can avoid contributing to the spread of invasive species by not releasing swordtails and other nonnative fish into natural waterways.

The swordtail is a medium-sized fish. The female is slightly larger and can measure up to 16 centimeters (6.3 inches) in length. Even though the male has a much longer tail, it only grows up to 14 centimeters (5.5 inches) long. 

The female swordtail’s size impacts the number of fry she produces. Larger females tend to give birth to more fry, though other factors — like ammonia and the frequency of feeding — can also affect fertility. Females ranging in size from 6.35 centimeters to 7.62 centimeters (2.5 inches to 3.0 inches) produce the most fry.

The swordtail tends to be a resilient fish, but it still needs species-appropriate care to survive. The minimum swordtail fish tank size is 10 gallons. Use a heater to maintain a warm water temperature between 64°F to 82°F (17°C and 27°C). The water should have a pH range of 7 to 8 and a dGH range of 12 to 30.

You can keep the swordtail in a community tank with other tropical fish. Popular tank mates for the swordtail include angelfish, mollies, and peaceful Corydoras. Avoid housing the swordtail with bigger fish that could eat it.

The swordtail is an omnivorous fish. In the wild, typical swordtail fish food includes crustaceans, insects, plants, and worms.

Pet swordtails can eat fish flakes and freeze-dried or live foods. Many breeders feed their swordtails a commercially formulated trout diet with color enhancers or pigments to brighten the fish’s color.

It’s relatively easy for pet owners to breed swordtail fish at home. Both genders reach sexual maturity around 10 to 12 weeks and can interbreed with other species in the poeciliid family. 

The species is live-bearing, so the female fertilizes and incubates eggs internally. She can store viable sperm in the oviducts and use it to fertilize five to nine consecutive broods. The gestation period can vary depending on temperature and may last anywhere from 26 to 63 days. After this period, the female gives birth to live young. 

The optimal tank temperature for breeding swordtails is between 22°C and 26°C (74°F to 78°F). The fish will stop producing fry if the temperature drops below 15°C (59°F). 

You should provide floating plants for the fry to hide. Adult swordtails will eat their young, so place them in a separate tank to keep the fry safe.

The swordtail’s ability to survive various conditions and temperatures makes it an excellent pet for beginning fish owners. Many people enjoy purchasing ornamental swordtails with unique colors and fin variations. And because this species is so easy to breed, you can even try to produce your own hybrid or ornamental swordtails. If you’re looking for an attractive and resilient pet, the swordtail can make a wonderful addition to your aquarium.