The Swordtail Xiphophorus hellerii is extremely popular. It is one of the prettiest aquariam fish and very hardy. In the wild, it has an olive green body with red and yellow along the sides and sometimes colorful speckles on its fins. With this coloration, it is most commonly called the Green Swordtail or the Red Swordtail. However, in captivity, it has been bred into the fabulous colors that make it so highly prized today.
The Green Swordtail is similar in shape to both the Platy fish and the Guppy. It has a bulkier body than either of those two, though, and also has a "sword" extending from the bottom of the male's tail fin. It is often thought to be named for the "sword" shaped extension of its tail fin, but the Swordtail was actually named for the sword-like appearance of the male's anal fin. This specialized anal fin develops as the male fish matures. The middle rays of the anal fin are modified into a narrow copulatory organ called a gonopodium.
Indeed, the beautiful male's "sword" tail is one of the most striking physical characteristics possible in any aquarium fish. Even though this dramatic tail fin has no apparent purpose, it accounts for anywhere from 1/4 to 1/3 of the total length of the fish! The wild species have an even more majestic tail, with swords up to 6 inches (15 cm) in length. The sword is shorter in tank-bred specimens but complemented by the wonderful colors that are now available.
What's in the name?
"bearing a sword"
Like the Platy fish, Swordtails have been interbred to produce all kinds of interesting colors and different types of finnage. Some of the more common varieties of the Swordtail are Red, Red Wag, Red Tux, Painted, Neon Green, Marigold (and wag), Pineapple, Black, Red Twin bar, Sunset, and Gold Tuxedo.
Some other types of Swordtail fish that are occasionally available are the Montezuma Swordtail (Spotted Swordtail) Xiphophorus montezumae, Delicate Swordtail Xiphophorus cortezi, and Mountain Swordtail Xiphophorus nezahualcoyotl. A couple of dwarf species, the Pygmy Swordtail Xiphophorus pygmaeus and Panuco Swordtail Xiphophorus nigrensis, are sometimes available. These dwarves are similar to the others but smaller and not quite as hardy.
Swordtail fish are not only pretty but easy to breed and fast-growing. They are quite hardy and thus make wonderful fish for the beginner. They are generally peaceful, lively fish that swim in loosely grouped schools and thrive in a community. They do best in a well-planted tank with lots of room to swim around. Provide floating plants to protect the young as the parents often eat their fry. Like all livebearers, they do like a bit of salt, though it is not necessary.
The Green Swordtail Xiphophorus hellerii was described by Heckel in 1848. They are found in North and Central America, where they range from the Atlantic slopes of southern Mexico (Rio Nantla, Veracruz) to northwestern Honduras. They have been introduced to, and become established in, a number of countries in southern Africa and along the eastern coast of Australia.
Wild strains exist in many color variations of the Green Swordtail X. hellerii. These fish are not endangered nor are they listed on the IUCN Red list of Threatened Species. Other common names this species is known by are Swordtail and Red Swordtail.
There are a variety of other Swordtails species that are occasionally available. These include the Montezuma Swordtail (Spotted Swordtail) Xiphophorus montezumae, Delicate Swordtail Xiphophorus cortezi, and Mountain Swordtail Xiphophorus nezahualcoyotl. A couple of dwarf species, the Pygmy Swordtail Xiphophorus pygmaeus and Panuco Swordtail Xiphophorus nigrensis, are sometimes available.
The Spotted Swordtail Xiphophorus montezumae was introduced into the aquarium hobby as early as 1864, while the popular Green Swordtail was first introduced in 1909. The Green Swordtail X. hellerii is the most available. The other species, though similar, are not always as large and are often more delicate.
The Green Swordtail are found in all types of waters, and prefer heavily-vegetated areas. They are mostly found in rivers and streams, but are also found in warm springs, canals, and ponds. Though not a schooling fish, they enjoy the company of other swordtails and will often shoal. They feed on plant matter, worms, crustaceans, and insects.
Scientific Name: Xiphophorous hellerii
Social Grouping: Groups - Enjoys being with other Swordtails even though it is not a schooling fish.
IUCN Red List: NE - Not Evaluated or not listed
The Green Swordtail is moderate in size with a sturdy, elongated body. Females are larger, reaching up to 6.3 inches (16 cm) in length while the males are somewhat smaller at 5.5 inches (14 cm). Along with Mollies, Guppies, and Platy fish, the Swordtail is a member of the Poeciliidae family of Live-bearing Toothcarps, which are distinguished by having teeth in both their upper and lower jaws.
Swordtail males are smaller and slimmer than females and have a "sword" on the caudal fin (tail fin). As the male fish matures, the middle rays of its anal fin modify into a narrow copulatory organ called a gonopodium.
The wild Swordtail has an olive green body with red, yellow, or brownish stripes along the lateral line of the sides. They can also have speckles on the dorsal fin and sometimes on the caudal fin. The "sword" on the caudal fin is yellow with a lower black edge. In nature, mutations occur frequently, so wild strains also have many color variations.
Selectively bred variations of the Green Swordtail come in many colors and mixtures of colors. These variations include colors such as red, green, black and albino, though red is the most well known.
Green Swordtail - green body with a red, lateral zig zag pattern.
Green Wagtail Swordtail - Green Swordtail crossed with a Wagtail Platy.
Green Tuxedo Wagtail Swordtail - Green Swordtail crossed with a Tuxedo Wagtail Platy.
Red Swordtail - red ground cover overlaid with a dark red; a cross between the Green Swordtail and the Red Platy. Other red varieties are the Bloodred Swordtail, Brickred Swordtail, and Velvet Red Swordtail.
Red Wagtail Swordtail - Green Swordtail crossed with a Red Wagtail Platy.
Red Tuxedo Wagtail Swordtail - Green Swordtail crossed with a Red Tuxedo Wagtail Platy.
Variegated Swordtail - a mixture of colors with no set pattern.
Hybrid Swordtail - the same fish as the Salt-and-Pepper Platy. If they retain the "sword," they are called a Hybrid Swordtail rather than Salt-and-Pepper Platy. No two fish are alike but all contain bits of black, red, yellow, and green blotches.
Black Nubian Swordtail
Pineapple Swordtail (female)
The average lifespan of Swordtail fish is between 3-5 years, though they can live longer with optimal care.
Size of fish - inches: 6.3 inches (16.00 cm) - Females can get up to 6.3 inches (16 cm) in length while the males are somewhat smaller at 5.5 inches (14 cm).
Lifespan: 5 years - On average, these fish will live about 3-5 years, but if well cared for, they can live even longer.
Fish Keeping Difficulty
The Swordtail fish is hardy and generally peaceful, making it suitable for community tanks. It is easy to care for and to breed, making it a great choice for the beginning aquarist. Make sure you select only healthy fish and provide a good tank and varied diet to offset any potential problems.
A male can demonstrate territorial aggression towards other males, however, and sometimes toward other fish, especially older males. It is best to keep only one male or to have several to divert their aggression. Also, the Swordtail is an accomplished jumper, so be sure to provide a secure cover for the aquarium.
Aquarium Hardiness: Very Hardy
Aquarist Experience Level: Beginner
Foods and Feeding
Since they are omnivorous, the Swordtail fish will generally eat all kinds of fresh, frozen, and flake foods. In the wild their diet consists of worms, crustaceans, insects, and some plant matter. In the aquarium, they will gladly eat most commercially-prepared fish foods as well as supplementary live and vegetable-based food. Feed brine shrimp (either live or frozen), tubifex,, or blood worms as a treat. This fish is not a picky eater but should be fed a varied diet several times daily in small amounts.
Diet Type: Omnivore - This fish is an omnivore; however, it appreciates a high vegetable component in its diet. Supplementing processed foods with blanched lettuce is an excellent way to facilitate this need.
Flake Food: Yes
Tablet / Pellet: Yes
Live foods (fishes, shrimps, worms): Some of Diet
Vegetable Food: Some of Diet
Meaty Food: Some of Diet
Feeding Frequency: Several feedings per day - Feed small amounts several times a day--what the fish can consume in about 3 minutes each time.
The Swordtail fish does not require special aquarium care and is not too demanding about tank conditions. Still, the tank should have regular water changes of 25% every 2-4 weeks. The tank may need more or less frequent water changes depending how many fish there are and the condition of the water.
As with most of this family, it is also advisable to add 1-1.25 teaspoons of aquarium salt per gallon. Be sure to only replace water with salted water during water changes. Water that evaporates will leave salts behind, so there is no need to add more salt if you are topping off evaporated water.
Water Changes: Monthly - Do water changes of 25% every 2-4 weeks, or more often with heavily-stocked tanks.
The Swordtail fish are moderately-sized, active fish that need plenty of room for swimming. A 15 gallon tank could house a single individual with some tankmates, but this fish will be much happier in at least a 20 gallon tank with a few of its own kind for company. Generally, it is best to keep a single male with a small harem of females unless the tank is large enough to house a more evenly mixed group. Be sure the tank is covered as they are accomplished jumpers.
Most any type of gravel works fine for a substrate, but these fish will appreciate an aquarium that is well-planted. They are tolerant of water conditions, but good filtration is very helpful in maintaining stable water. Filtration systems remove much of the detritus, excess foods, and waste. This, in turn, helps to keep the tank clean and maintains the general health of the fish.
Minimum Tank Size: 20 gal (76 L) - Fifteen gallons could house a single individual, but a small group needs at least a 20 gallon tank.
Suitable for Nano Tank: Yes
Substrate Type: Any
Lighting Needs: Moderate - normal lighting
Temperature: 64.0 to 82.0° F (17.8 to 27.8° C)
Range ph: 7.0-8.3
Hardness Range: 12 - 30 dGH
Brackish: No - This is not a brackish water fish, but it does appreciate a little salt in the water of about 1-1.25 teaspoon per gallon of water.
Water Movement: Moderate
Water Region: Middle - These fish will swim in all areas of the aquarium, but mostly in the middle.
Swordtail fish are generally peaceful, lively fish that swim in loosely-grouped schools. They are generally considered a good community fish though sometimes they will eat their own, and other fishes', fry. Males get aggressive with each other, so a ratio of one male to several females works best. Aside from that, individual fish vary from being peaceful, harmonious tankmates to being bullies. Older males especially can tend toward aggressiveness with each other and other species.
This fish combines well with most other good natured fish of similar size. However, the Swordtail's extensive fins can be too tempting for fin nippers to resist, so it is best to avoid combining them. Fishes such as Mollies, Platy fish, Angelfish, armored catfish (Corydoras) and plecostomus, and larger Characins such as the Black Skirt, Red Serpae, and Silver Tip make good tankmates.
Temperament: Peaceful - This is generally a peaceful community fish, but males can sometimes get aggressive, especially older males.
Same species - conspecifics: Yes - Males can get aggressive with each other, so it's best to keep one with a few females, or keep several males to divert aggression. They will chase and eat their fry.
Peaceful fish (): Safe - Because of the Swordtail's long fins, mixing it with fin nippers should be avoided.
Semi-Aggressive (): Threat
Aggressive (): Threat
Large Semi-Aggressive (): Threat
Large Aggressive, Predatory (): Threat
Slow Swimmers & Eaters (): Safe
Shrimps, Crabs, Snails: Safe - not aggressive
Sex: Sexual differences
Only the male has the "sword" extension on the bottom of the tail fin. The male is also slimmer and has a "sword" shaped anal fin called a gonopodium. The female has a fan shaped anal fin, is rounder of body, and will have a spawning patch at breeding time.
There is an occasional tendency for a female Swordtail to change sex and develop a "sword" on her tail, especially when old or affected by parasites. She may even attempt courtship with another female, though the majority of the time they are infertile.
Breeding / Reproduction
This live-bearing fish breeds readily in the home aquarium without special attention if well fed and cared for. In fact, they can quickly overpopulate an aquarium. To breed Swordtails, little more is required than to introduce both sexes into the aquarium. Although they generally attain sexual maturity at about 8 to 12 months, they have been known to start breeding as young as 3 months of age.
On occasion, with certain environmental conditions, a female of this species has a tendency to undergo sex reversal. She may develop a "sword" on her tail and may attempt to spawn with another female, though most of the time this female will be infertile.
To selectively breed Swordtails, provide a breeding tank that is 10 to 20 gallons in size with gentle filtration. You will notice a female is pregnant when she develops a gravid spot, a dark mark on her abdomen. The gestation period is about 24 to 30 days.
Monitor the fish closely when she is close to giving live birth. Swordtails will chase their fry and may eat them if given a chance. The young will be consumed unless they are removed, isolated with a breeding trap, or simply given enough hiding spaces, such as densely rooted or floating plants. The female Swordtail can have between 20 and 200 fry, but they commonly have about 80. For more information, see the guide for breeding Livebearing Fish: Breeding Freshwater Fish - Livebearers.
Ease of Breeding: Easy
Swordtails are relatively hardy and do not have any particularly strong weaknesses for certain diseases. Still, they are subject to the same diseases as other tropical fish. One of the most common freshwater fish ailments is Ich. The best way to proactively prevent disease is to give them the proper environment and a well balanced diet. The more closely their aquarium resembles their natural habitat, the less stress the fish will have, making them healthier and happier. A stressed fish is more likely to acquire disease.
Anything you add to your tank can introduce disease. Not only other fish but plants, substrate, and decorations can harbor bacteria. Take great care and make sure to properly clean or quarantine anything that you add to an established tank so as not to upset the balance. For information about fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.
The Swordtail fish is among the most commonly available and is usually modest in price.
Samantha - 2016-05-02 Hello. I just started my first aquarium about a week ago. I'm sad to say that I was not educated properly before I added fish to my tank as I only thought you had to get the temperature right for them. Well all of the fish I added to my tank died in less than a day, so I started doing research online. I waited several days before I added new fish. I brought home a test kit to be sure that it would be safe for new fish to live in. So I added 2 male red swordtails. One looks totally fine but he sits at the bottom of the tank a lot and I haven't yet seen him eat. The other one moves more, but he appears to have the clamped fin? But last night after I turned the light off to the aquarium, his fin flared out more. Today, neither of them ate any of the food I put in for them this morning and aren't moving around much. Someone please help! I really hope they're not sick and we're gonna lose more fish!
Nordic - 2016-05-17 Hey add 1g aquarium salt to every 10L of water to your tank. Fishes my be suffering from initial bad parameters. The salt will help them feel better.
wyatt Shaw - 2014-12-28 i have two tuxedo platies and two ornage platies and a red swordtail i just got them yesterday and i am new to this aquarium thing but i was really wanting to get an eel i have excelllent hiding spots in the 50 gallon tank including a brick and some rocks stacked to create a tight hole but i am worried about the eel eating the other fish what should i do and what type of eel should i get if i do get an eel????
Clarice Brough - 2014-12-29 Sounds like a great tank! You could add one of the Spiny Eels, like the Zig Zag Eel, that don't get too big. They stay close to the bottom, feed on small foods like worms and brine shrimp... and mostly ignore their tankmates.
amalsyikin - 2014-11-22 I've just realized that my swordtail was having the babies when she's dead. I took her body out from the tank and saw her babies were still inside the womb(didn't noticed alive or not). I buried them at my backyard :(.. My question : 1) what may caused the dead? The mother is stressed because of giving birth? Or else? 2) should i took out the babies out of the womb? thank you (who replied me the answers :) )
arriyah - 2014-11-22 you should have took the babies out of the womb