Swordtails – Detailed Guide: Care, Diet, and Breeding

Swordtail (Xiphophorus hellerii) – Detailed Guide Care, Diet, and Breeding

Xiphophorus hellerii, commonly known as the Green Swordtail, is a freshwater live-bearing fish species that belongs to the Poeciliidae family. This particular type of fish has been a staple in the aquarium hobby for a long time and is highly praised by enthusiasts.

Swordtails are a popular choice for beginner aquarists due to their ease of care since these fish are very adaptable, demanding, and omnivores. Lots of food, lots of plants, and a moderate water flow will make these fish breed like crazy.

This comprehensive care guide offers essential information on the Swordtails, covering everything from breeding to maintaining their health and well-being in a home tank.

Quick Notes about Swordtail 

Name Swordtail
Other Names Green Swordtail
Scientific Name Xiphophorus hellerii
Water type Freshwater
Tank size (minimum) 15 gallons (~60 liters)
Keeping Easy
Breeding Easy
Size 4 – 5 inches (10 – 12 cm)
Optimal Temperature 71 – 78°F (22 – 26°С)
Optimal PH 7.0 – 8.0 
Optimal GH 5 – 20 
Dwellers Top-Middle
Nitrate Less than 60
Diet Omnivore
Temperament Peaceful
Life span up to 5 years
Color Form Wild color: olive-green or light brown
Ornamental variations: red, orange, black, gold,
spotted, neon, albino, silver, blue, etc

Etymology of Xiphophorus Hellerii

Xiphophorus hellerii is named in reference to the elongated shape of the male’s tail fin.

The name Xiphophorus is derived from the Greek words ‘Xiphos” meaning ‘Sword’ and ‘Pherein’ meaning ‘to bear’.

The species name, Hellerii, is a tribute to Arnold Edward Ortmann (1858–1909), a German-American zoologist and ichthyologist who was known as Alfred Heller in the United States.

Distribution of Swordtail 

Despite being considered native to areas of Belize, Guatemala, Honduras, and Mexico, this fish species is currently found in more than 35 countries in the World.

For example, the species was introduced and has become established in southern Florida, California, the Lake Mead area of Arizona and Nevada, Hawaii, Canada, Puerto Rico, Africa, Sri Lanka, Australia, Guam, Fiji, Czech Republic, Hungary, Germany, Italy, United Kingdom, Poland, Israel, Hong Kong, Egypt, Syria, Jordan, and even Iran.

Note: This is partly due to aquarium enthusiasts releasing the fish into local water bodies. Although because of its popular ornamental status, Swordtails are not considered as a “pest” species, this species is still listed on invasive species databases.

It is important to remember that any alien species can alter ecosystems, causing the loss of native species, and having major economic consequences.

Natural Habitat of Swordtail 

Xiphophorus hellerii is a versatile species that can thrive in a wide range of habitats, from fast-flowing streams and rivers that are abundant in vegetation to slow springs and their outflows.

They can also be found in weedy canals, ponds, and other aquatic environments such as rocky arroyos, ditches, and open lagoons with diverse substrates.

Despite varying water conditions, these fish can adapt to clear, murky, or muddy water, and even survive in heavily polluted areas.

This flexibility in habitat selection allows Swordtails to successfully colonize diverse aquatic environments.

Although this species is most abundant in freshwater, it is occasionally reported also in brackish water (up to 15 ppt.). Although such salinity is out of the species habitat preference, Swordtails can still tolerate it for some time.

Description of Swordtail 

Swordtail (Xiphophorus hellerii) – Detailed Guide Care, Diet, and Breeding - profileXiphophorus hellerii is a medium-sized, colorful, and active fish. Adult males are typically smaller than females, growing up to 3 – 3.5 inches (8 – 9 cm) in length, while females are usually about 4 – 5 inches (10 – 12 cm) in length.

Distinguishing characteristics of the Swordtails:

  • The body of Xiphophorus hellerii is elongated and laterally compressed, with a slightly curved back.
  • This species has a small, upturned mouth with small teeth that are used for grasping and shredding food.
  • The body shape of the species is similar to that of other livebearing fish, with a prominent anal fin, dorsal fin, and caudal fin.
  • The base color of Xiphophorus hellerii is typically olive-green or light brown.
  • Both males and females have a distinctive dusky, brownish, or redmid-lateral stripe that runs horizontally along the body, starting from the base of the tail and extending to the head. In some Swordtail varieties, 2 additional reddish stripes may be present above the mid-lateral line and one beneath.
    Note: It is believed that this lateral line is a sensory organ used to detect movement and vibrations in the water.
  • Males also have a very long straight caudal appendage that can sometimes grow almost as long as their bodies. The lower rays of the caudal fin are elongated into a conspicuous, usually pigmented, like a “sword.” 

Swordtail varieties (color and fins):

Over the course of many years, Swordtails have undergone selective breeding to produce various colors (red, orange, black, gold, spotted, neon, albino, silver, blue, etc.) and fin (hifin, sailfin, lyretail, etc.) variations for decorative purposes.

Ornamental distributors currently offer more than 50 different strains of Swordtails, with new ones being added regularly. Therefore, it will be absolutely pointless trying to name all of them here.

Interesting fact: Most of the existing Swordtail varieties available today were mainly produced through the hybridization of the Swordtail and Platy fish.

Lifespan of Swordtail 

At present, there are no exact data on how long Xiphophorus hellerii can live in the wild.

It is presumed that wild specimens have a lifespan of about 2 – 3 years. However, in captivity, with proper care and a suitable environment, they can live up to 5 years or slightly more.

It is important to note that the lifespan of Swordtails can vary depending on factors such as predation, genetics, water quality, diet, and overall care. With optimal conditions and proper care, Swordtails can live a long and healthy life.

Typical Behavior of Swordtail 

Sociality:

Swordtail (Xiphophorus hellerii) – Detailed Guide Care, Diet, and Breeding - profile 2
photo credit to Valentin Hintikka

Swordtails are considered to be social fish that can be kept in community tanks with other peaceful fish species. It is a good idea to keep them in groups of at least 3-4 individuals. Ideally, you need to have 3-4 females per 1 male.  

Being in a group allows them to engage in natural behaviors, which will reduce stress and improve their overall well-being.

Temper:

Their temper is generally peaceful, but Swordtail fish may also have the habit of biting the fins of other fish regardless of their size.

Male swordtails can be somewhat aggressive towards each other, especially if they are kept with females and in small groups. Males establish dominance hierarchies and compete for access to females.

In a contest that usually lasts more than an hour, the winners and losers can be identified by their behavioral and physical traits.

  • The loser is typically marked by darker coloration, optional vertical stripes, folded fins, a head-down position, and is being situated on the edge of the tank.
  • The winner typically exhibits spread fins, no darkening or vertical stripes, and moves actively around the tank.

It is generally recommended to keep only one male swordtail with several females or to keep a group of males with plenty of space and hiding places to reduce aggression.

Interesting fact: Restricted food early in life has long-turn consequences. Such males often become subordinate to size-matched opponents. Basically, early developmental trajectories can shape the physiology and behavior of the adults.

Activity:

Swordtails are active swimmers. Therefore, it is not advisable to keep them with fish that are too calm or small, as they can be intimidated by the sudden moves of these fish.

Placement in Tank:

Swordtails tend to occupy the upper and middle sections of the tank, with occasional visits to the bottom. However, they don’t particularly favor the bottom area.

Features:

  • Social: Yes
  • Activity: Moderate
  • Placement: Top and middle dwellers
  • Peaceful: Yes
  • Nippers: Yes
  • Jumpers: Yes

Feeding Swordtail 

Xiphophorus hellerii is a diurnal omnivore. Studies of the stomach contents of the swordtails indicated that both terrestrial and aquatic insects are eaten along with phytoplankton and some macroalgae.

Nonetheless, a significant difference is also observed between the diet of juveniles and adults (i.e. juveniles consumed greater quantities of aquatic invertebrates, zooplankton, phytoplankton, etc. whereas adults consume more vegetable components).

In the aquarium, the Swordtails can be fed with a wide variety of meals such as:

Experiments were performed to investigate the influence of different levels of Spirulina (0, 1, 3, 5, and 8%) on feed consumption, growth, fertility, and coloration. Results showed that growth rate, mean body length, and weight increased as levels of Spirulina increased.  Fish fed 8% Spirulina performed better than those fed lower levels.

Spirulina contains 60-70% protein by weight, is the richest source of vitamins B12 and beta carotene, and is loaded with essential fatty acids and minerals. Essential amino acids (62%) such as isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophane, and valine are present in Spirulina.

Other experiments showed that low protein diets (20% and 30%) produced the lowest specific growth rate values, compared to 40 % and 60 % dietary treatments. At the same time, there was no significant difference between 40% and 60% treatments.

How to Improve Coloration of Swordtails? 

Carotenoids are natural lipid-soluble pigments that are primarily synthesized in plants, including phytoplankton and algae, and contribute to the wide range of colors found in nature.

These pigments typically manifest as various shades of yellow, orange, and red. Unlike plants and algae, fish cannot produce carotenoids on their own and must acquire them from their diet.

Therefore, it is recommended that feeds containing color enhancers or pigments such as astaxanthin should be fed to bring out the full color of the Swordtails, such as (links to amazon):

How Often to Feed Swordtail?

Adult Swordtails should be fed twice per day

Fry should be fed 3 times per day. They eat a lot and grow really fast.

How Much to Feed Swordtail?

Stick to the so-called “five-minute rule”. This technique means that fish should consume all the food within 3-5 minutes.

Features:

  • Diet Type: Omnivore
  • Food Preference: Meat
  • Feeding Frequency: Daily

Are Swordtails Plants Safe?

Yes, these fish are completely plant safe. They will not eat any healthy plants in the tank. This specie does not eat living plant material.

Keeping and Caring for Swordtails 

Swordtails can tolerate a wide range of temperatures, salinity, hardness, and dissolved oxygen, in the water.

Although they are pretty hardy and can withstand varied ranges of water parameters, we still need to address their core needs!

Important: Make sure that you cycle your tank before bringing these fish home. Once the tank is cycled you need to check the quality of the water using a test kit.

Tank size:

Swordtails should not be kept in small tanks due to their size. The minimum tank size for this species is 15 gallons (60 liters) for 1 male and 3 – 4 females.

Important: As Swordtails are very jumpy, to prevent it from happening, there are a few things you can do:

  • get a lid for the tank,
  • lower the water level,
  • keep floating plants,
  • do not stress your fish.

Related article:

Water parameters:

Temperature: Swordtails are able to withstand temperatures that vary greatly. According to the study, the lethal minimum temperatures ranged from 41 – 52°F (5.5 – 11.3°C). 

Important: It does not mean that the temperature in your tank can fluctuate that much in short periods of time! The range of their tolerance is strongly influenced by acclimation temperature.
In other words, fish that are acclimated at lower temperatures can extend their lower temperature tolerance further compared to fish acclimated to higher temperatures.

In the aquarium, they will thrive in warm temperature conditions of 71 – 78°F (22 – 26°С).

Interesting fact: Temperature also affects the body shape of Swordtails during their early development. For example, under high temperatures, Xiphophorus hellerii has a deeper head and body shape. Lower temperatures lead to a pointy head, longer tail, and a dorsal position of the pectoral fin forming a fusiform body shape.

pH: Swordtails generally prefer slightly alkaline conditions. The ideal pH range should be between 7.0 – 8.0.

Hardness: These fish can live in any water but they will appreciate optimal GH between 5 – 20.

Water Flow:

It is not a requirement. Although Swordtails prefer moderate water flow, they will be absolutely fine everywhere.

Lighting:

No special requirements. 

Swordtails have a distinct diurnal activity pattern, which is synchronized with the light/dark and feeding cycles.

Lighting should be adapted to the needs of plants in the tank.

Related article:

Substrate:

No special requirements.

Although you can choose any substrate for the tank, it is better to have a dark color so that the fish look more contrasting against its background.

Plants and Decorations:

The natural habitat of Swordtails is abundant in vegetation. Plants provide good hiding spots for them. It makes them happy and playful.

This should be replicated in their tank.

You can use floating plantsfake plantsdriftwoodleaves, and small rocks to provide additional hiding spots for them.

Water Changes:

You will have to change 20-25 % of their water every week. However, you may need to remove a different percentage of water depending on your filter and other tank factors.

Keep in mind that any water that you add to the tank should also be at least dechlorinated.

Note: Dechlorinators can be purchased at any pet store, (Seachem Prime – link to check the price on Amazon), to make sure the water is safe for your fish.

Salt:

While some hobbyists recommend using 1-1.5 teaspoons of aquarium salt per gallon (4.5 liters) (for its disease-preventing benefits, etc.), it is important to note that it is not a mandatory practice.

Nonetheless, if you do choose to use salt, make sure to only replace water with salted water during water changes. This is because when water evaporates, it leaves salts behind, so adding more salt to top off evaporated water is unnecessary.

Swordtail – Male and Female Differences

Swordtail (Xiphophorus hellerii) – Detailed Guide Care, Diet, and Breeding - sexing
photo credit to Zaraza

Xiphophorus hellerii is sexually dimorphic. Adult males and females are very easily identified.

  • Size. Females are larger than males.
  • Belly. Females have rounded bellies, compared to slim males.
  • Gonopodium. Males possess a modified anal fin called a gonopodium, which is used during the mating process for sperm transfer to females which has internal fertilization and sperm storage. 

Breeding Swordtails

Breeding these fish is very easy. Thus it can be a rewarding experience even for beginner hobbyists. Swordtails are a livebearing species, meaning that the females give birth to fully-formed, swimming fry instead of laying eggs.

Livebearers will reproduce as long as adequate feeds are available and appropriate temperatures are maintained.

Here is the full process.

Maturity:

Xiphophorus hellerii attains sexual maturity at 1 – 1.2 inches (2.5 – 3 cm), when they are about 10-12 weeks of age.

“Early” and “Late” Males

Swordtails can have so-called “early” and “late” males. There has been a long-standing debate among enthusiasts, with some claiming that late males are infertile while others attribute this to unfavorable conditions such as high or low temperature, acidity, etc.

However, science and practice indicate that early swordtail males carry a larger number of male genes. Therefore, if we use early males for breeding, the offspring will have more males, while if we use late males for breeding, the offspring will have more females.

Female to Male Changes

Another interesting feature of swordtails is that some adult females, including those that have given birth multiple times, can transform into males – their fin becomes similar to that of males.

This usually happens due to sudden fluctuations in water parameters, which can cause hormonal imbalances. However, some hobbyists believe that this occurs when there are not enough males in the aquarium.

Unfortunately, such individuals cannot fertilize or carry fry.

Mating:

Once they reach sexual maturity, Swordtails do not form monogamous mating pairs and instead exhibit complete polygamy.

Even more, male Swordtails will court and mate with females of their own species, as well as with females of other poeciliid species, resulting in hybridization.

Experiments showed female preference for large males with a longer conspicuous “sword” ornament.

Male to Female Ratio: A good rule of thumb is to keep a male to female ratio of 1:4 in your breeding tank. This will ensure that there are enough females to keep the males from overzealously pursuing a single female and that there will be enough diversity in the gene pool of the fry.

Fertilization:

Females undergo internal fertilization, which means that the male deposits sperm inside the female’s body to fertilize the eggs.

After fertilization, some of the male’s sperm may remain in the folds of their oviducts for fertilizing mature eggs when needed. It allows females to reproduce again without a male’s involvement.

According to the study, from a single mating event, a female can give birth up to 9 consecutive broods, as viable sperm for fertilization can be provided for up to 2 years!

Brooding (Gestation):

In Swordtails, embryonic development may vary from 26 to 63 days, depending on the temperature. At 76 – 78°F (24 – 26°C) the gestation period usually ranges from 26 to 30 days.

The number of fry also correlates with the temperature. Experiments showed that the number of fry per spawn tends to increase by 3 with every one-degree rise in water temperature, on average. For example:

  • The highest average number of fry can be found in water with a temperature of 84°F (29°C).
  • Below temperatures of 59°F (15°C), fry production is reported to cease,
  • When temperatures drop below 64°F (18°C) or rise above 86°F (30°C), production significantly slows down.

Under optimal conditions, all adult females will have eggs in different embryonic development.

Fecundity

These fish are prolific breeders. The fecundity of Xiphophorus hellerii has been reported to be as high as 242 fry per female.

Aquarists noticed that young females usually have a low number of fry (20-50) compared with experienced females (100 – 150). On the other hand, the fry of mature females are significantly smaller.

Fry:

Ensuring the survival of the fry is perhaps the most important part to follow when breeding Swordtails.

As soon as you notice that the female is about to start giving birth, it’s better to put her in a special hatchery box for breeding. The fry that hatch fall down and slip through a gap in the bottom of the hatchery box.

Unfortunately, parents often consume their own fry, since the fry are relatively large and have bright colors, this can lead to a substantial loss.

Note: Keep in mind that in the wild, Swordtails rarely see their fry since the fry are immediately carried away by the current.

Therefore, once the fry are born, they should be separated from the mother (and other fish) to avoid predation.

A separate fry tank with a sponge filter and gentle water flow is recommended. The fry should be fed a high-quality diet (such as artemia, cyclops, chopped blackworms, etc.) 3 times a day and the water should be changed frequently.

The fry grow rapidly, and by the age of 2nd months, the anal fin of the males begins to change, while by the 3rd month, their “sword” starts to grow.

Swordtails and Suitable Tankmates

When it comes to suitable tankmates, Swordtails can coexist with a variety of other peaceful fish species that share similar water parameter requirements.

Nonetheless, keep in mind that Swordtails can become nippy, especially if kept with fish with long fins (such as Betta)

  • Fish

If you still decide to keep this species in community tankssome good options include: Southern platyfish, NeonsEndlersPygmy CoryDanio RerioGuppy, Harlequin Rasboras, Dwarf Chain loaches, Ghost Glass Catfish, Mollies, etc.)

  • Dwarf shrimp

It is not recommended to keep Swordtails with dwarf shrimp. Swordtails are significantly larger and may see dwarf shrimp as prey and try to eat them.

Shrimplets and molting shrimp will be easy snacks for them.

Nonetheless, if you are not convinced and still decide to keep Swordtails and dwarf shrimp together, it will be crucial to provide plenty of hiding places and cover for the shrimp. Dense plantings, driftwood, and caves can give your shrimp at least some chance of survival.

It is always best to be on the side of caution when it comes to mixing fish and invertebrates.

  • Freshwater snails

Yes, Swordtails can generally be kept with snails without issue.

In fact, freshwater snails can make good tankmates for Swordtails, as they help keep the tank clean by consuming uneaten food and algae.

Avoid:

  • Large and/or aggressive, and/or boisterous fishes.
  • Keep them away from all types of crayfish and most types of freshwater crabs. 

Related article:

Problems Associated With Swordtails

Even though Swordtails are generally known for their resilience, they are still susceptible to diseases resulting from infections caused by Protozoa (Trichodina), Monogenea (Dactylogyrus and Gyrodactylidae), and Fungi (Saprolegnia).

To prevent such illnesses, it’s recommended to keep new fish in a separate container for 10 – 14 days before introducing them to the main tank.

In order to avoid fungal infections, it’s important to maintain a clean environment for the fish and avoid the buildup of waste and uneaten food. When feeding live food, it’s best to purchase it from specialized stores and rinse it with running water before feeding it to your pets.

The symptoms of illnesses in live-bearing fish can vary, but typically include:

  • lethargy,
  • loss of appetite,
  • floating to the top,
  • sinking to the bottom,
  • damage to fins (they may split or stick together).

If your Swordtails exhibit any of these signs, it is best to isolate it in a separate container to prevent the spread of the disease to other fish in the aquarium.

A formalin bath at a concentration of 250 ppm for 1 h/day for five consecutive days is recommended to treat the fish.

In Conclusion

Swordtails are a great choice for beginner aquarists due to their ease of care, adaptability, and forgiving nature.

While they are not very demanding, it is important to keep in mind that they still have their own preferences when it comes to their environment. By taking these preferences into consideration and providing proper care, Swordtails can thrive and add beauty to your tank.

Related article:

References:

  1. Maddern, M. G., H. S. Gill, and D. L. Morgan. “Biology and invasive potential of the introduced swordtail Xiphophorus hellerii Heckel (Poeciliidae) in Western Australia.” Aquatic Conservation: Marine and Freshwater Ecosystems 21, no. 3 (2011): 282-291.
  2. Rosenthal, Gil G., and Christopher S. Evans. “Female preference for swords in Xiphophorus helleri reflects a bias for large apparent size.” Proceedings of the National Academy of Sciences95, no. 8 (1998): 4431-4436.
  3. Basolo, Alexandra L. “Female preference for male sword length in the green swordtail, Xiphophorus helleri (Pisces: Poeciliidae).” Animal Behaviour40, no. 2 (1990): 332-338.
  4. Tamaru, Clyde S., Brian Cole, Rich Bailey, Christopher Brown, and Harry Ako. A manual for commercial production of the swordtail, Xiphophorus helleri. Center for Tropical and Subtropical Aquaculture, 2001.
  5. James, Raja, Kunchitham Sampath, Ramasamy Thangarathinam, and Iyyadurai Vasudevan. “Effect of dietary Spirulina level on growth, fertility, coloration and leucocyte count in red swordtail, Xiphophorus helleri.” Israeli Journal of Aquaculture-Bamidgeh58 (2006).
  6. Chong, Alexander SC, Saraitul Dahlianis Ishak, Zulfaizuddin Osman, and Roshada Hashim. “Effect of dietary protein level on the reproductive performance of female swordtails Xiphophorus helleri (Poeciliidae).” Aquaculture234, no. 1-4 (2004): 381-392.
  7. Benson, Kari E., and Alexandra L. Basolo. “Male–male competition and the sword in male swordtails, Xiphophorus helleri.” Animal Behaviour71, no. 1 (2006): 129-134.
  8. Rashidian, Ghasem, Simona Rainis, Marko D. Prokić, and Caterina Faggio. “Effects of different levels of carotenoids and light sources on swordtail fish (Xiphophorus helleri) growth, survival rate and reproductive parameters.” Natural Product Research35, no. 21 (2021): 3675-3686.
  9. Tuckett, Quenton M., Jared L. Ritch, Katelyn M. Lawson, Larry L. Lawson, and Jeffrey E. Hill. “Variation in cold tolerance in escaped and farmed non-native green swordtails (Xiphophorus hellerii) revealed by laboratory trials and field introductions.” Biological invasions18 (2016): 45-56.
  10. Royle, Nick J., Jan Lindström, and Neil B. Metcalfe. “A poor start in life negatively affects dominance status in adulthood independent of body size in green swordtails Xiphophorus helleri.” Proceedings of the Royal Society B: Biological Sciences272, no. 1575 (2005): 1917-1922.
  11. Beaugrand, Jacques P., and René Zayan. “An experimental model of aggressive dominance in Xiphophorus Helleri (pisces, poeciliidae).” Behavioural Processes10, no. 1-2 (1985): 1-52.
  12. KALLMAN, KLAUS & Walter, Ronald & MORIZOT, DONALD & KAZIANIS, STEVEN. (2009). Two New Species of Xiphophorus (Poeciliidae) from the Isthmus of Tehuantepec, Oaxaca, Mexico, with a Discussion of the Distribution of theX. clemenciae Clade. American Museum Novitates. 3441. 1-34. 10.1206/0003-0082(2004)441<0001:TNSOXP>2.0.CO;2.
  13. First confirmed record of an established population of green swordtail (Xiphophorus helleriiHeckel, 1848) in Europe Pencho Pandakov, Zhivko Barzov, Radoslav Moldovanski and Helena Huđek Manag. Aquat. Ecosyst., 422 (2021) 31.
  14. H. Hieronimus, Guppies, Mollies, and Platies, Complete Pet Owners Manual Series, Barron’s, 2009

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