Do Swordtails Need a Heater?

Swordtails need a heater in their aquarium because they require temperatures between 72 and 82 degrees to grow and thrive in their environment. While they can potentially survive without one, it’s highly recommended to add a heater in a swordtail fish aquarium.

Swordtails, which are often mistaken for guppies or platies, are freshwater tropical fish native to South American rivers. They’re used to warm temperatures and are extremely cold-sensitive, so they require temperatures similar to their native environment to survive.

In this article, we’ll take a deep dive into the reasons why swordtails need a heater installed in their aquarium. Be sure to stick around because we’ll also go over the best aquarium heater for swordtails.

Do Swordtails Need a Heater?

Swordtails are tropical fish, and they need warm water for their survival. That’s why unless you live in a tropical region, swordtails need a heater in their aquarium to keep the water at an ideal temperature for them to live in.

Adding a heater to a swordtail aquarium can improve the fish’s health, growth rate, and reproductivity. It can also reduce the likelihood of diseases.

This isn’t to say that swordtails can’t survive without a heater, but they’ll only survive, not thrive. Swordtails need warm temperatures to stay healthy and flourishing. Low temperatures, however, can make them uncomfortable and ill.

One thing to keep in mind is that the room temperature where your aquarium is affects the heater. So, if you’re not using a heater that automatically adjusts water temperature, you’ll need to regularly check the heater’s temperature.

Red Swordtail on Black Gravel with Rock Female

Ideal Temperature for Swordtails

Swordtails prefer temperatures ranging from 72 to 82 degrees Fahrenheit. They can withstand higher temperatures, but it isn’t the best situation for them.

Swordtails can also survive in temperatures ranging from 65 to 72 degrees Fahrenheit. However, anything lower than 65 degrees Fahrenheit is potentially life-threatening.

If the aquarium temperature drops below 65 degrees Fahrenheit, swordtails may become inactive and their health may suffer. They might even lose their colors.

Can Swordtails Survive Without a Heater in an Aquarium?

Swordtails can probably live without a heater, but it can make an aquarium much more habitable for the fish and allow them to thrive.

Without the heater, the aquarium is prone to constant temperature fluctuations or low temperatures, which can have harmful consequences to a swordtail’s health.

Poor Physical Health

If temperatures drop in the aquarium, swordtails become more susceptible to contracting diseases and parasites, such as fin rot, ich, and cottonmouth. Constant cold temperatures eventually weaken the fish’s immune system.

What’s more, swordtails can experience itchiness due to parasites or disease infections. This condition can irritate them and put them under severe stress, weakening their immune system even more.

If a swordtail becomes ill frequently and isn’t properly treated, the situation may become life-threatening.


Swordtails have difficulty adapting to new environments, so they can immediately sense any sudden changes in temperatures.

When the temperatures in an aquarium constantly fluctuate between slightly warm and cold, swordtails can become extremely anxious and uneasy.

As a result, the fish may experience considerable stress, which is detrimental to their physical and mental health.

In addition, if a swordtail is stressed, it may lose its appetite, become more aggressive, and even bully other fish in the aquarium.

Growth Challenges

Maintaining warm temperatures in a swordtail aquarium is imperative to the fish’s growth and development.

Swordtails kept in cold waters are often frail, sick, and stressed. Due to the poor physical and mental health, the fish’s ability to properly grow is hampered.

Similarly, a sudden drop in temperatures can stunt the fish’s sword-like extension.

Reproduction Issues

Low temperatures tend to make swordtails inactive and stressed, so they’re less likely to breed if the aquarium is cold.

Even if the fish breeds, the swordtail fry are unlikely to survive in temperatures lower than 75 degrees Fahrenheit.

How Many Heaters Should a Swordtail Aquarium Have?

Ideally, a swordtail aquarium should have at least two heaters to prevent temperature fluctuations. In fact, any tropical fish aquarium should have a minimum of two heaters.

The reason tropical fish like swordtails need multiple heaters is that maintaining stable and proper warm temperatures is critical to their survival.

When your aquarium has more than one heater, it prevents any temperature fluctuations in case one breaks down.

In addition, if the aquarium is kept in a cold room, a single heater may be insufficient to raise and maintain the required temperature. A second heater, however, will help increase the aquarium’s temperature to the desired level of warmth.

As a general rule, you should have a primary heater set to the required temperature and a secondary heater set a degree or two lower.

Best Aquarium Heater for Swordtails

The best aquarium heaters for swordtail aquariums are submersible heaters. Just as the name suggests, these heaters are fully submerged in the water. They have a low voltage thermostat that allows them to automatically maintain the aquarium temperature.

Most submersible heaters should be installed beneath the filter output to heat the water as it enters the aquarium. As a result, they maintain a constant flow of heated water circulating throughout the aquarium.

Another advantage of submersible heaters is that they take up little space, leaving you with plenty of room for other decorations.

Remember to turn off the heater if you:

  • Intend to change the water
  • Move the aquarium or heater

Submersible heaters must remain submerged, so removing them from the water while they’re turned on risks damaging the heating element.

In Conclusion

Swordtails, like any other living organism, thrive when they’re placed in favorable living conditions. Because they’re tropical fish, they require warm water temperatures. They don’t do well in temperatures that are below 65 degrees Fahrenheit.

In addition, sudden temperature drops or constant temperature fluctuations can weaken swordtails’ immune systems, making them susceptible to infections, diseases, and parasites.

That’s why placing a heater or two in the aquarium can be an excellent preventative measure to keep your swordtails alive and healthy.

Aside from that, swordtails are lovely small fish that are easy to care for and can coexist with most other fish species with similar characteristics. You’ll love having swordtails in your aquarium!