Swordtail fish are among the most popular and widely kept freshwater aquarium fish. Known for their vibrant colors and active nature, these fish generally exhibit a peaceful demeanor, making them suitable for community tanks. However, individual temperaments can vary. While some swordtails may be timid and shy, others—particularly males—can display aggressive behavior, especially towards one another.
It’s important to consider the social dynamics when housing swordtail fish. Males may establish hierarchies and may become territorial, particularly if space is limited. For a harmonious aquarium, providing plenty of hiding spots and ensuring a balanced male-to-female ratio can help mitigate aggression.
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Habitat in the wild
The swordtail is a popular freshwater fish belonging to the family Poeciliidae, known as the livebearer family. Its scientific name is Xiphophorus hellerii, derived from the Greek words “xiphos,” meaning “sword,” and “phoros,” meaning “to carry.” The species name “Helleri” honors Karl Bartholomäus Heller, a German naturalist who first collected the fish in Mexican lakes and introduced it to Europe. In 1848, the fish was formally described by Dr. Johan Hekel, a laboratory assistant at the Imperial Natural History Museum in Vienna.
Native to Central America, particularly Mexico, swordtails are commonly found in aquariums worldwide due to their vibrant colors and active nature. They inhabit various freshwater environments, primarily along the Atlantic coast of Mexico, Guatemala, and Honduras. Swordtails thrive in both swift mountain rivers and calmer lower river reaches, as well as in lakes, bogs, and lagoons. They prefer shallow, densely planted areas where they feed on a diverse diet of insects, algae, and detritus. These habitats are characterized by warm water temperatures and abundant vegetation, which provide both food and shelter.
Description
Size
Swordtail fish can reach a significant size, with males typically growing to about 4 inches (11 cm) in length. Females are generally larger, reaching around 6.3 inches (16 cm) excluding the tail. However, the size of swordtails can be smaller in aquarium settings, largely depending on the tank conditions and overall care provided. Factors such as a nutritious diet, optimal water parameters, and sufficient space can significantly contribute to the healthy growth of your swordtail fish. Ensuring they have plenty of room to swim and hide is crucial for their well-being.
Lifespan
In captivity, the average lifespan of swordtail fish is typically around 2 to 3 years. However, with proper care, a healthy environment, and good husbandry practices, swordtails can potentially live longer. Some well-cared-for individuals have been known to live up to 5 years or even slightly longer. Regular water changes, appropriate feeding, and maintaining stable water conditions can help maximize their lifespan.
Body
The body of the swordtail is elongated and flattened from the sides. A distinctive feature of this fish is its unusual tail shape, which resembles a sword and is the source of its name. The extension of the lower caudal fin is more pronounced in males and plays a vital role in visual displays and mating behaviors. Females typically have a more rounded and less elaborate fin. The tail can either be rounded with one ray or may feature several rays, contributing to the variety of appearances among different individuals.
Coloring
When it comes to coloring, swordtails boast a wide array of patterns, making it difficult to pinpoint just one. The most common coloration is red with a black tail, but there are numerous hybrids and variations that display a range of colors and patterns. This diversity is a result of selective breeding and natural genetic variation, which allows aquarists to choose from a multitude of stunning appearances for their tanks.
| Characteristic | Description |
|---|---|
| Scientific Name | Xiphophorus hellerii |
| Family | Poeciliidae (Livebearer family) |
| Origin | Central America, primarily Mexico and northern Central America |
| Habitat | Freshwater streams, rivers, ponds, and ditches with vegetation |
| Size | Adult males: 2.5 – 4 inches (6 – 10 cm), Adult females: 3 – 5 inches (7 – 12 cm) |
| Lifespan | Average 2 – 3 years in captivity, longer with proper care |
| Body Shape | Streamlined, slightly elongated body with distinct dorsal and anal fins |
| Fin Features | Males have an elongated lower caudal fin (“sword”), females have a more rounded fin |
| Colors | Various colors and patterns, including red, orange, black, and combinations |
| Behavior | Active and social fish, compatible with many community fish |
| Water Temperature | 70 – 82°F (21 – 28°C) |
| Water pH | 7.0 – 8.5 (slightly alkaline to neutral) |
| Water Hardness | Slightly hard to moderately hard water |
| Diet | Omnivorous, eats algae, plants, insects, and small crustaceans |
| Reproduction | Livebearers: Females give birth to live fry, store sperm for multiple batches |
| Tank Requirements | Well-planted aquarium, hiding spots, gentle water flow |
| Compatibility | Generally peaceful, compatible with other peaceful community fish |
| Sexing | Males have the distinctive “sword,” females have a rounded anal fin |
| Special Considerations | Provide both plant-based and protein-rich foods, monitor water quality closely |
Difficulties in keeping
Swordtail fish are among the most popular choices for beginner aquarists. Their hardy nature and manageable size make them an excellent option for those new to the hobby. They are relatively easy to care for and can adapt to a range of water conditions, which adds to their appeal.
Keeping in the tank
Tank Size
The recommended tank size for swordtail fish varies based on several factors, including the number of fish you plan to keep, the presence of other tank mates, and the available space in your home. Swordtails are active swimmers and thrive in larger tanks that provide ample room for movement. Here are some guidelines to consider:
Minimum Tank Size: For a small group of swordtails, consisting of one male and two to three females, a tank with a capacity of around 20 to 30 gallons (75 to 113 liters) is generally considered the minimum. This size allows for adequate swimming space and provides the females with areas to retreat if the male becomes overly aggressive. Keeping one male with multiple females helps reduce stress on the females, as a single male paired with one female can lead to constant harassment, potentially causing stress and even death.
Larger Groups: If you plan to keep more swordtails, consider increasing the tank size accordingly. A larger group may require a tank in the range of 40 to 55 gallons (150 to 208 liters) or more to accommodate their active nature.
Males and Territories: Male swordtails can be territorial and may exhibit aggressive behavior towards other males. To alleviate aggression, provide hiding spots and break up the line of sight in the tank. Avoid overcrowding with males, as a dominant male will chase other males, leading to fights, injuries, and stress.
Providing more space than the minimum requirement contributes to the health and well-being of your swordtails and the overall stability of the aquarium. Consider the number of fish, their behaviors, and compatibility with other species when determining the appropriate tank size.
Water Parameters
Swordtail fish are generally adaptable and not overly demanding when it comes to water parameters. However, sudden fluctuations in water quality can cause stress and health issues. Regular monitoring and maintenance are essential for their well-being. Here are the recommended water parameters for swordtails:
Temperature: Swordtails thrive in water temperatures ranging from 70 to 82°F (21 to 28°C). Keeping the water within this range is crucial for their health and stress prevention.
pH Level: They prefer slightly alkaline to neutral conditions, with a recommended pH range of 7.0 to 8.5. Maintaining stable pH levels is important, so avoid rapid fluctuations.
Water Hardness: Swordtails tolerate various water hardness levels but do best in slightly hard to moderately hard water, ideally around 8 to 20 dGH.
Ammonia, Nitrite, and Nitrate: Ammonia and nitrite levels should be maintained at zero, as they are toxic to fish. Monitor nitrate levels, keeping them below 40 ppm to avoid negative health impacts.
Water Quality: Regular water changes are vital for maintaining good water quality. Aim for partial changes of about 20% to 30% of the tank volume every 1-2 weeks to remove waste and replenish essential minerals.
Filtration and Aeration: Efficient filtration and gentle water movement are essential for maintaining water quality. Choose an appropriate filter for your tank size and consider adding an air stone or bubbler for better aeration.
Chlorine and Chloramine: Tap water often contains chlorine or chloramine, which can harm fish. Always treat tap water with a water conditioner to neutralize these chemicals before adding it to the aquarium.
Tank Decor
When setting up the tank, keep in mind that swordtails are not only agile swimmers but also capable jumpers. Ensure the tank is covered to prevent accidental escapes, which could lead to injuries or fatalities.
You can choose decorations based on your preferences, but ensure that the tank is thickly planted. Dense vegetation provides hiding spots for females to evade aggressive males and offers a safe haven for fry, helping them avoid predation. The presence of plants enhances the overall aesthetics of the aquarium while creating a more comfortable environment for your swordtails.
Swordtails benefit from having plenty of hiding spots and plants in the tank. Live plants provide shelter, improve water quality, and create a more natural environment. When determining the tank size, consider the space occupied by plants and decorations.
Tank mates
The swordtail fish is considered to be a peaceful one, but my experience shows that it’s not always true. They have very strong intrageneric aggression. Besides, old males may attack other fishes in a tank, but this depends on a specific temper.
Some fishes live peacefully and some of them become bully, start haunting young males and other fishes. Small tanks without plants encourage aggressive behavior of the fish. What you definitely shouldn’t do, is to keep two or more swordtail males in one tank. This guarantees fights in the tank.
Though they will not kill each other, but constant stress leads to death of the weakest male. There are two ways how you can settle the issue: keep one male and 3-4 males in a tank or lots of males in a spacious tank with females.
This way there is no obvious leader between the swordtail fish and aggression in spread uniformly (not just one and the same fish suffers). As a rule, they tend to be neutral to their tank mates.
So, the best tank mate is fish of the same size, but not a predator one.
This can be:
- Harlequin Rasboras (Trigonostigma heteromorpha)
- Neon Tetras (Paracheirodon innesi)
- Ember Tetras (Hyphessobrycon amandae)
- Glowlight Tetras (Hemigrammus erythrozonus)
- Black Neon Tetras (Hyphessobrycon herbertaxelrodi)
- Cardinal Tetras (Paracheirodon axelrodi)
- Rummy Nose Tetras (Hemigrammus rhodostomus)
- Dwarf Gouramis (Trichogaster lalius or Trichogaster chuna)
- Sparkling Gouramis (Trichopsis pumila)
- Celestial Pearl Danios (Danio margaritatus)
- White Cloud Mountain Minnows (Tanichthys albonubes)
- Dwarf Rasboras (Boraras spp.)
- Endler’s Livebearers (Poecilia wingei)
- Guppies (Poecilia reticulata)
- Platies (Xiphophorus spp.)
- Corydoras Catfish (Corydoras spp. – pygmy cory, panda cory, adolfoi catfish)
- Otocinclus Catfish (Otocinclus spp.)
- Bristlenose Plecos (Ancistrus spp.)
Diet
Swordtails are omnivorous fish, thriving on a diverse diet that includes both plant and animal-based foods. A well-balanced diet is essential for their health and vitality. In the wild, their diet primarily consists of thin algae and other fouling, so replicating this diversity in captivity is crucial.
High-Quality Flake or Pellet Food
A reliable staple for swordtails is high-quality flake or pellet food designed for tropical fish. Look for options rich in essential nutrients, including proteins, vitamins, and minerals. This will form the foundation of their diet, ensuring they receive the necessary nutrients for growth and overall health.
Live Foods
Swordtails particularly enjoy live foods, which closely mimic their natural diet. Offering live foods such as brine shrimp, daphnia, and bloodworms can be a delightful treat. These foods are especially beneficial for breeding pairs and developing fry, providing essential protein that supports healthy growth.
Frozen Foods
Frozen foods are a convenient and nutritious alternative. You can find frozen brine shrimp, daphnia, and other small aquatic organisms in pet stores. Be sure to thaw and rinse frozen foods before feeding to ensure they are safe and palatable for your fish.
Vegetables and Algae-Based Foods
While swordtails are not strictly herbivorous, incorporating some plant matter into their diet is beneficial. Offer blanched vegetables such as spinach, zucchini, and lettuce as occasional treats. Additionally, algae-based foods, available in wafer or pellet form, can provide a source of natural fiber. Since maintaining significant amounts of algae in a tank is impractical, consider purchasing flakes with vegetable supplements to form a basic component of their diet.
Specially Formulated Diets
Some commercial foods are specifically formulated for livebearers like swordtails, containing a mix of plant and animal-based ingredients tailored to their nutritional needs. These diets can be a great addition to their feeding regimen.
Feeding Frequency and Portion Control
Feed your swordtails small amounts multiple times a day rather than one large feeding. This approach mimics their natural feeding behavior and helps prevent overfeeding, which can lead to water quality issues.
Variety
Providing a varied diet helps prevent nutritional deficiencies and encourages natural foraging behaviors. Rotate between dry, frozen, live, and vegetable-based foods to keep your swordtails engaged and healthy.
Gender differences: male vs female
It is extremely easy to see between swordtail fish male and female. Male and female swordtail fish (Xiphophorus hellerii) have distinct differences in their appearance and behavior. Here are some key characteristics that differentiate male and female swordtails:
Male Swordtail:
- Sword Tail: The most prominent feature of male swordtails is their elongated lower caudal fin, often referred to as the “sword.” Only male has a sword on its tail. This fin extends beyond the rest of the tail and gives the fish its name.
- Size: Males are generally smaller than females, with an average length of about 2.5 to 4 inches (6 to 10 cm).
- Coloration: Male swordtails tend to have more vibrant and colorful patterns compared to females. They often display a combination of colors, including red, orange, black, and sometimes blue or green.
- Gonopodium: ust like all live-bearing fish the anal fin of the male has been modified into a tube (gonopodium) and the female has a wide anal fin. This specialized fin is used for mating and differs in shape from the female’s anal fin.
- Behavior: Male swordtails are known to exhibit more territorial and aggressive behaviors, particularly towards other males and sometimes towards females. They may chase other fish, especially if they feel threatened or during mating displays.
Female Swordtail:
- Anal Fin: The anal fin of females is rounded and lacks the modified structure found in males. It does not serve a reproductive function like the gonopodium.
- Size: Females are generally larger than males, with an average length of about 3 to 5 inches (7 to 12 cm).
- Coloration: Female swordtails usually have more subdued and less vibrant colors compared to males. Their coloration might include shades of gray, silver, or pale yellow.
- Pregnancy: Female swordtails are livebearers, which means they give birth to live fry. When pregnant, they may develop a gravid spot near their anal fin, which is a dark area that indicates the presence of developing fry.
- Behavior: Female swordtails are generally less aggressive than males and tend to be more social with other fish in the tank. They may seek hiding spots when pursued by aggressive males.
When keeping swordtails in a community tank, it’s recommended to have more females than males to reduce aggression and stress on the females. Providing plenty of hiding spots and plants can also help alleviate aggression. Observing the differences between male and female swordtails will not only help you identify their sex but also give you insights into their behaviors and interactions within the aquarium.
Breeding
Is a live-bearing fish, that is its juveniles appear not as eggs, but as a completely formed small fish. The swordtail fish male fertilizes eggs inside the females body and she carries them till she is ready to spawn. Usually this period lasts for 28-30 days.
It is very easy to get juveniles, just like from other live-bearing fish (guppy, molly). The female fish can even spawn without the male, because she stores male milt inside her and can fertilize the eggs herself. Therefore, if the female fish spawned and there is no male fish in a tank, this is the case.
Swordtail becomes reproductive at the age of 5-6 month. For breeding (and also for the fish to feel comfortable) it’s recommend to keep the fish in ratio – 1 male for 3 females.
The easiest way to stimulate breeding is to raise the temperature of tank water. Ammonia and nitrates level should be as low as possible and pH 6.8-7.8. When the female becomes fatter watch the dark spot near her anal fin.
As the spot gets darker and the fish becomes significantly fat, the spawning will happen very soon. This dark spot is actually juveniles eyes which are seen through her body. The female spawns from 15 to 100 and more juveniles at a time. Spawning usually occurs in the morning.
It seems to me, that the most important rule you should follow when breeding swordtail – its taking care of its juveniles. Unfortunately, parents eat their own offspring. Taking into account that juveniles are quite large and brightly colored – it looks like extermination.
In the wild swordtail fish never sees its offspring, since the juveniles go with the water flow right after they are born. In the tank parents take them for food. To save the offspring the tank should be thickly planted. Plants are put on the tank bottom, in the water and they should be especially thick on the water surface.
This way you provide the juveniles with shelter from aggressive parents and most of juveniles survive.
Also to safe the offspring you may use a special depositing hopper – the swordtail female stays in it and the juveniles fall into a spawning tank after they are born. This way you prevent any contact between the offspring and its parents.
The third option to keep the juveniles safe is to remove their parents from the tank right after spawning. This is an easy way, but it in this case aquarist should be attentive and timely.
Juveniles are large, active and hungry. You can feed them with egg yolk, food for juveniles and brine shrimp nauplii. It’s desirable to add spirulina or flakes with vegetable supplements. Provided with spirulina+live food diet the juveniles will grow fast and have bright coloring.