Black Swordtail

Black Swordtails are enchanting freshwater fish that bear a close relationship to the colorful Platies. With their distinguished black coloration and signature "sword" tails, they have secured their place in the hearts of aquarium hobbyists. These sociable fish demand low upkeep, making them an optimal choice for community aquariums.

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Care DIfficulty


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Central America

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5 inches (12 cm)

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5 years

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Table of contents

Origin, Appearance, Size, and Lifespan

The Black Swordtail, scientifically known as Xiphophorus hellerii, is a well-liked freshwater fish primarily originating from Central America, specifically from Honduras to Mexico and Guatemala. They are typically found in fast-flowing rivers and streams in the wild, teeming with vegetation.

In their natural habitats, Black Swordtails are most commonly found in flowing waters with an ample amount of plant life, which serves as both a shelter and a food source. The earth-toned riverbeds contrast with their dark coloration, enhancing their visibility. These social creatures flourish in groups, often seen in considerable numbers.

Their native environment boasts warm, moderately hard, and slightly alkaline water. The temperature usually ranges between 70 to 80 degrees Fahrenheit (21 to 27 degrees Celsius), with a pH level of 7.0 to 8.3, and water hardness between 10 to 15 dGH. To recreate a similar environment in your aquarium, maintain a steady water temperature, utilize a high-quality filtration system, and introduce live plants and rocks.

By closely replicating the Black Swordtail's natural surroundings and assuring the correct water conditions, you'll be providing your fish with the groundwork for a robust and contented life in your aquarium.

Black Swordtails are admired for their distinctive black coloration and signature elongated, sword-like tail, giving them a unique and striking presence in aquariums. Although they are moderately-sized fish, reaching up to 4 to 5 inches (10 to 12 cm) in size, their distinct silhouette and lively behavior make them a prime choice for those wanting an engaging, striking aquatic display. These captivating fish bring delight to observers as they energetically explore the tank, cementing them as a treasured favorite among enthusiasts of all skill levels.

Given proper care, Black Swordtails can have a lifespan of up to five years. As social creatures, they thrive in groups and are best kept in schools of at least five individuals. To boost their well-being and ensure longevity in captivity, it's crucial to provide an aquarium rich in vegetation with plenty of hiding spots, as well as a varied diet comprising of high-quality flakes, pellets, and frozen foods.

Fun Facts

Having familiarized ourselves with the appearance and lifespan of Black Swordtails, let's delve into some intriguing facts about these unique fish that make them a highlight of the aquarium hobby. From their striking tails to their dynamic behavior, Black Swordtails are full of marvels that will certainly charm any aquarist.

  • Adaptable Swimmers: In their natural habitat, Black Swordtails are known for their ability to navigate a variety of water conditions. They can thrive in fast-flowing rivers as well as still ponds and lakes, demonstrating their remarkable adaptability.
  • Color Variety: Although we are focusing on the Black Swordtail, it's interesting to note that this species comes in a variety of other colors too. The array ranges from red, orange, and yellow to even green and multicolored variants, which all share the distinct sword-like tail.
  • Sword-bearing Species: Black Swordtails belong to the Poeciliidae family, which is known for their live-bearing reproduction method. This means, unlike many other fish species, they give birth to live young rather than laying eggs, adding to their unique appeal.
  • Sexual Dimorphism: One of the most intriguing aspects of Black Swordtails is their sexual dimorphism. Only male Black Swordtails possess the signature "sword" tail, while females lack this distinct feature. This makes it fairly easy to differentiate between sexes within this species.
  • Active Swimmers: Black Swordtails are active swimmers and are known for their dynamic behavior. They not only add movement to the tank but also interact with various elements of the aquarium, making them an engaging sight for the observers.

Now that you've learned some interesting facts about Black Swordtails, you'll be better positioned to appreciate their charm and idiosyncrasies in your aquarium. In the following section, we'll offer recommendations on tank setups, ensuring your Black Swordtails have an ideal environment to prosper and exhibit their fascinating characteristics.

Recommended Tank Setups

This guide includes the fundamental components—tank, filter, heater, lighting, substrate, and more—to ensure you can establish a suitable environment for Black Swordtails and other compatible freshwater fish species in your aquarium. From economical to high-end setups, you will have diverse options for customization, aesthetics, and advanced features. Black Swordtails enjoy being in groups, and keeping them with other fish helps maintain their well-being. Black Swordtails are typically priced between $2 and $4 per fish, although prices can fluctuate based on size, quality, and availability.

Budget-friendly setup (around $200):

  • Tank: 20-gallon aquarium with a hood or glass canopy ($40 - $70)
  • Filter: Hang-on-back (HOB) or sponge filter rated for 20 gallons ($20 - $40)
  • Heater: 50-100 watt adjustable aquarium heater ($15 - $30)
  • Lighting: Basic LED aquarium light ($20 - $50)
  • Substrate: Affordable aquarium sand or small gravel ($10 - $20)
  • Decor: A few pieces of driftwood and rocks, along with cost-effective live plants like Java Fern and Anubias ($20 - $40)
  • Fish: Minimum 4, maximum 8 Black Swordtails ($20 - $30)
  • Thermometer: $3 - $10
  • Substrate Vacuum: $10 - $25
  • Fish Net: $2 - $10
  • Algae Scraper or Magnetic Cleaner: $5 - $20
  • Siphon and Bucket: $15 - $30
  • Test Kit: $15 - $50
  • Fish Food: $5 - $20
  • Water Conditioner: $5 - $15

Mid-range setup (around $400 - $650):

  • Tank: 20-30 gallon aquarium with a hood or glass canopy ($60 - $120)
  • Filter: Canister filter or high-quality HOB filter rated for the tank size ($60 - $150)
  • Heater: 100-150 watt adjustable aquarium heater ($25 - $50)
  • Lighting: LED aquarium light with adjustable settings for plant growth and color enhancement ($50 - $150)
  • Substrate: Nutrient-rich aquarium substrate designed for planted tanks ($20 - $40)
  • Decor: A mix of driftwood, rocks, and live plants such as Amazon Swords, Java Fern, Anubias, and Cryptocoryne species ($40 - $80)
  • Fish: Minimum 6, maximum 10 Black Swordtails ($30 - $40)
  • Thermometer: $3 - $10
  • Substrate Vacuum: $10 - $25
  • Fish Net: $2 - $10
  • Algae Scraper or Magnetic Cleaner: $5 - $20
  • Siphon and Bucket: $15 - $30
  • Test Kit: $15 - $50
  • Fish Food: $5 - $20
  • Water Conditioner: $5 - $15

High-end setup (above $800):

  • Tank: 30-40 gallon rimless aquarium with a glass canopy ($120 - $250)
  • Filter: High-quality canister filter rated for the tank size ($100 - $250)
  • Heater: 150-200 watt adjustable aquarium heater with an external temperature controller ($40 - $80)
  • Lighting: Advanced LED lighting system with customizable settings for plant growth, color enhancement, and day/night cycles ($150 - $300)
  • Substrate: Premium aquarium substrate designed for planted tanks, with added root tabs for extra plant nutrition ($30 - $60)
  • Decor: A combination of driftwood, rocks, and live plants to create a natural aquascape, featuring plant species such as Amazon Swords, Java Fern, Anubias, Cryptocoryne species, and carpeting plants like Dwarf Hairgrass or Monte Carlo ($60 - $150)
  • Fish: Minimum 8, maximum 15 Black Swordtails ($40 - $60)
  • Thermometer: $3 - $10
  • Substrate Vacuum: $10 - $25
  • Fish Net: $2 - $10
  • Algae Scraper or Magnetic Cleaner: $5 - $20
  • Siphon and Bucket: $15 - $30
  • Test Kit: $15 - $50
  • Fish Food: $5 - $20
  • Water Conditioner: $5 - $15

Please bear in mind that these figures are merely suggestions, and you should consider other factors such as tank companions and individual fish temperaments when deciding how many Black Swordtails to accommodate in your aquarium. Prices may vary depending on location, brand, and availability.

Set Up Your Tank

Previously, we discussed the best possible aquarium setups for your Black Swordtails and their companions. With those requirements in mind, we will now provide a step-by-step guide to setting up your aquarium. These steps will help you in choosing an appropriate location for your aquarium, cleaning and getting it ready, installing all the essential equipment, and preparing the water through cycling to ensure a safe and healthy environment for your fish. Additionally, we'll also go over the correct procedure to acclimatize your Black Swordtails and their tank mates to their new environment. Following these guidelines will set you on the path to establishing a flourishing aquatic habitat for your fish.

  • Step #1: Identify an ideal location for your aquarium, ensuring it's shielded from direct sunlight, heaters, and cold drafts. Confirm the surface is even and robust enough to handle the weight of a filled tank. If you need a stand for your aquarium, assemble it as per the manufacturer's guidelines and place the empty tank on top.
  • Step #2: Begin by cleaning the aquarium using clean water (do not use soap or detergents) to remove any dust or other particles. Wipe the interior with a clean cloth or paper towel. Rinse your chosen substrate, such as sand or gravel, in a bucket until the water comes out clear. Spread this substrate across the base of the tank, creating a subtle gradient towards the back for a sense of depth.
  • Step #3: Prior to adding water to the aquarium, map out your desired layout including the positioning of equipment like filters and heaters. This will make setting up and maintaining the tank easier in the future. Install the filter and heater as per the manufacturer's guidance. If you opt for a sponge or under-gravel filter, position it below the substrate before you add the water.
  • Step #4: Decorate the aquarium with elements such as driftwood, rocks, and plants to create interesting hiding spots and visually appealing spaces, while ensuring enough open areas for your fish to swim. Be cautious when arranging these elements to avoid damaging or obstructing your equipment. Plants can be fastened to rocks or driftwood to keep them secure.
  • Step #5: Fill the tank with water that's been treated with a water conditioner if your tap water contains chlorine or chloramines. Use a clean plate or plastic bag on the substrate to prevent disruption while pouring water. Fill the tank up to two-thirds of its capacity. Attach your aquarium light to the hood or canopy, following the instructions provided by the manufacturer. Consider using a timer to regulate the light, maintaining a steady day-night cycle, which is crucial for your fish and plants. Plug the heater, filter, and any additional equipment (like air pumps, CO2 systems) into the power supply, and place the thermometer where it can be easily read.
  • Step #6: Continue filling the tank with water, leaving some space between the water surface and the top of the tank for oxygen exchange. Switch on the heater, filter, and any other equipment. Keep an eye on the water temperature and adjust the heater accordingly. Let the tank go through a cycling period of 4-6 weeks to enable the growth of beneficial bacteria and stabilize the water conditions. During this period, you can add a bacterial starter culture to expedite the process. Use a test kit to monitor the levels of ammonia, nitrite, and nitrate in the water.
  • Step #7: After the cycling process, when the water parameters have stabilized, gradually acclimate your Black Swordtails and other fish to the new tank conditions before introducing them. Start by letting the unopened fish bag float in the tank for 15-20 minutes to equalize the temperature. Then, open the bag and introduce a small volume of tank water into it. Continue to add small volumes of tank water every 5-10 minutes over the course of 30-60 minutes, letting the fish slowly get used to the new water chemistry. Using a net, gently move the fish from the bag to the tank, avoiding unnecessary stress and the potential introduction of bag water into the aquarium.
  • Step #8: After all the fish have been introduced, establish a routine feeding schedule, providing suitable quantities of high-quality food specific to your species. Regularly change 20-30% of the water every 1-2 weeks and use a test kit to monitor water parameters, ensuring a healthy environment for your fish. Keep a close watch on your fish for any signs of stress or sickness, especially in the first few weeks post-introduction. Be ready to intervene if necessary, such as modifying water parameters or seeking guidance from a seasoned aquarist.

By adhering to this step-by-step guide and incorporating the additional setup tips, you will be well on your way to creating a thriving aquatic environment where your Black Swordtails and their tank mates can thrive.

Recommended Water Parameters

For Black Swordtails to thrive, certain water conditions in your aquarium must be met. Here's a rundown of what you should aim for:

  • Temperature: A water temperature range of 72°F to 82°F (22°C to 28°C) should be maintained.
  • pH: Black Swordtails prefer neutral to slightly alkaline water, so keep the pH between 7.0 and 8.3.
  • Hardness: Aim for moderate hardness in the water (12-30 dGH).
  • Ammonia, Nitrite, and Nitrate: Ensure both ammonia and nitrite levels are at 0 ppm, while nitrate levels should be kept below 50 ppm.
  • Lighting: Moderate lighting suits Black Swordtails best, though they can adapt to a variety of lighting conditions.
  • Water movement: Black Swordtails are comfortable in moderate water flow, reminiscent of their natural riverine habitat.Regular water testing and necessary changes are crucial to maintain these parameters consistently.

Routine Water Maintenance

For a healthy Black Swordtail tank, regular water changes are paramount. They help get rid of surplus nutrients, waste, and potential toxins. Here's a recommended schedule:

  • Weekly water changes: Substitute 25-30% of the aquarium water every week.
  • Test water parameters: Keep an eye on pH, ammonia, nitrite, nitrate, and hardness regularly.
  • Use a gravel vacuum: Use this tool to clean the substrate during water changes.
  • Dechlorinate the water: Before adding tap water to the aquarium, treat it with a water conditioner.
  • Match temperature and pH: Ensure the new water matches the tank water in temperature and pH.
  • Acclimate the fish: Allow your fish time to adapt to new conditions after water changes.

Alongside these regular water maintenance practices, remember to:

  • Monitor lighting duration: Maintain a consistent 10-12 hour photoperiod to prevent excessive algae growth.
  • Plant maintenance: Trim live plants regularly to keep them healthy and remove any dead or decaying matter to prevent water quality issues.
  • Filter maintenance: Depending on the manufacturer's instructions, clean or replace the filter media every 4-6 weeks.

Diet and Feeding Schedule

Black Swordtails are omnivores, requiring a varied diet. Here are some feeding guidelines:

  • Flakes and pellets: High-quality flake or pellet food formulated for tropical fish should form the basis of their diet.
  • Frozen and live foods: Treat them occasionally with brine shrimp, bloodworms, daphnia, or mosquito larvae.
  • Vegetable matter: Supplement their diet with vegetable matter such as blanched spinach, zucchini, or cucumber.
  • Feeding frequency: Feed small portions two to three times a day, ensuring not to overfeed.

Stress and Diseases

Like all fish, Black Swordtails may exhibit stress due to various factors such as poor water conditions, aggression, or unsuitable tank conditions. Here's how to manage these issues:

  • Watch for stress signs: Monitor your Black Swordtails for signs of stress, such as unusual behavior like hiding, lethargy, color loss, or rapid breathing.
  • Check water quality: Regularly test your aquarium water and perform necessary water changes.
  • Monitor tank mates: Ensure that Black Swordtails are not being bullied or harassed by other fish.
  • Create a suitable habitat: Provide enough hiding spots and a suitably sized tank for your fish.

Black Swordtails are generally robust but can be prone to common fish diseases like:

  • Ich (white spot disease): This common parasitic infection causes white spots on the body and fins, lethargy, and appetite loss. Treat Ich with aquarium salt or anti-parasitic medication.
  • Fin rot: A bacterial disease that leads to frayed or discolored fins and tail. Treat fin rot with a partial water change, aquarium salt, and antibacterial medication.
  • Velvet disease: This parasitic disease causes a yellow or brownish velvet-like coating on the fish's body. Treat with an anti-parasitic medication.
  • Swim bladder disease: This affects a fish's buoyancy. Treat by fasting the fish and offering them blanched peas, and consider using an antibacterial medication if needed.


Breeding Black Swordtails can be an engaging task and is relatively straightforward:

  • Step #1: Set up a separate breeding tank with a temperature around 80°F (27°C), and a pH level of 7.0-8.3. Maintain moderate water hardness and include plants for cover.
  • Step #2: Choose healthy, mature Black Swordtails for breeding. The male's elongated tail, called a gonopodium, distinguishes it from the female.
  • Step #3: Prepare the breeding pair by providing a high-protein diet of live or frozen foods to boost their strength and energy.
  • Step #4: Once mating has occurred, the female can store sperm and produce multiple batches of fry over several months. No specific spawning trigger is required.
  • Step #5: After birth, remove the adult fish to prevent them from eating the fry. Provide the fry with infusoria or liquid fry food initially, gradually introducing crushed flake food as they grow.
  • Step #6: Keep an eye on the development of the fry and separate them by size if necessary to prevent cannibalism.

This step-by-step guide and the additional setup tips should help you in creating a flourishing aquatic environment for your Black Swordtails and their companions.

Recommended Tank Mates

Here are the top 10 recommended tank mates for Black Swordtails:

  1. Platies
  2. Mollies
  3. Guppies
  4. Tetras
  5. Corydoras Catfish
  6. Plecos
  7. Ghost Shrimp
  8. Zebra Snails
  9. Danios
  10. Rainbowfish

Avoid pairing Black Swordtails with aggressive or predatory fish, such as cichlids or larger barbs, as they might cause stress or even harm the Swordtails. Regularly monitor interactions between new fish and existing ones to prevent any aggression or stress towards the Swordtails.


Black Swordtails are a vibrant species of freshwater fish recognized for their unique tail shape and ease of care. These fish require specific water parameters, a balanced diet, and an appropriate environment to flourish in captivity. Given the right conditions, they can live up to five years and add a lively dynamic to any aquarium. When choosing tank mates, it's crucial to select non-aggressive and peaceful species to ensure a tranquil community. Breeding Black Swordtails can be an engaging endeavor for seasoned hobbyists, and success comes with patience and optimal conditions. All in all, Black Swordtails are an exciting and attractive species that can enhance any aquarium with their striking appearance and active behavior.

Frequently Asked Questions

What is the ideal tank size for Black Swordtails?

A 20-gallon tank is the minimum recommended size for Black Swordtails, providing ample space for a small group. Choosing a larger tank can further aid in maintaining stable water conditions and giving your fish sufficient room to swim.

How many Black Swordtails should be kept together?

Black Swordtails, being social fish, thrive in groups of at least 5-6 individuals. Maintaining a larger group promotes their natural behaviors and helps them feel safer and more at ease.

What water parameters do Black Swordtails require?

Black Swordtails thrive in water temperatures between 72°F and 82°F (22°C and 28°C), a pH between 7.0 and 8.3, and moderately hard water with a hardness of 12-30 dGH.

What do Black Swordtails eat?

Black Swordtails are omnivores and require a mixed diet. Feed them high-quality flake or pellet food, supplemented with occasional live or frozen foods such as brine shrimp and bloodworms, and vegetable matter like blanched spinach.

Are Black Swordtails compatible with other fish?

Yes, Black Swordtails are generally peaceful and can coexist with other similarly sized, non-aggressive fish species. Ideal tank mates include platies, mollies, tetras, and small catfish.

How can I differentiate between male and female Black Swordtails?

Males have a long, pointed lower fin (the "sword") and are generally smaller than females. Females lack the sword, have a rounder belly, and are usually larger.

How long do Black Swordtails live?

With proper care and optimal tank conditions, Black Swordtails can live for up to 3 to 5 years.

How do I breed Black Swordtails?

Breeding Black Swordtails is straightforward. They require standard water conditions, and no specific triggers are needed for spawning. Use a separate breeding tank, and provide cover for the fry to hide from adults, as they may eat the young.

Do Black Swordtails require a planted tank?

Although not strictly necessary, a planted tank is beneficial for Black Swordtails. Live plants offer hiding spots, contribute to better water quality, and create a more natural habitat that closely mirrors their wild environment.

Can Black Swordtails change color?

Yes, Black Swordtails can exhibit color changes due to stress, illness, or changes in water conditions. If you notice your Black Swordtails losing their color, it's crucial to check the water parameters and closely monitor their health.