Why are my Swordtails Dying?

Swordtail fish can live for almost 3-5 years inside an aquarium but they can die beforehand due to the negligence of the owner.

Why are my swordtails dying? If the swordtail is kept deprived of a clean tank and water without a sound filtration system, they will befall ill and die. Plus, if you overfeed them or feed them something poisonous, it might kill your fish.

In this article, we will learn about the potential causes of your dying swordtail. But first, we’ll discuss the symptoms of a sick swordtail fish so that you, the owner, can identify when your buddies feel ill.

Symptoms of a sick swordtail

The behavior of a normal healthy swordtail fish is very typical, it will keep moving around the tank all the time except for when it is sleeping. The variation in their behavior is very noticeable and such a change signifies that there is something wrong with the fish.

Sickness affects their swimming pattern, eating routine and physical appearance. By keeping regular tabs on these activities, you will be able to detect the sick fish. Early detection of unusual behavior and diseases can aid you in saving the fish’s life. Following are some common symptoms of a sick swordtail fish:

  • Red stripes on the body, changed color of fins, torn or jagged fins- all are signs of ammonia poisoning.
  • Rapid loss of scales and curved spines indicate the deteriorating health of swordtails.
  • If the swordtail has stopped eating suddenly, then it might be facing some health issue.
  • The sick swordtail fish’s eye will bulge out in an unusual manner.
  • If you notice the presence of sores or grey patches on the skin, then it could be a parasite attack.
  • The swordtail is sick if it is facing breathing problems or heavy breathing
  • If the swordtail has stopped moving and stuck to one corner of the tank, it shows that it is undergoing much sickness and stress.
  • If the swordtail is scratching its body against the plants or rocks, that is the indication of oodinium disease.

What are the common reasons for swordtail death?

Often, pet swordtails die at home aquariums sooner than expected. Most of the time, these fish die due to their owner’s negligence. So, you have to make sure that you have taken all the precautionary measures for their proper care to ensure a healthy and long life for them.

Following are some common reasons behind the sudden death of swordtails in an aquarium:

  • Stress
  • Toxic water
  • Ammonia poisoning
  • Overfeeding
  • Diseases
  • Killing beneficial bacteria

3 Reasons Why Aquarium Fish Die (Video)


Swordtail fish cannot handle stress for too long or they end up dying. Stress is the most common cause behind the mortality of swordtails. But how can you find out if the fish is stressed? Following are some typical signs which indicate the stress among fish:

  • Glass surfing: If your fish is continuously moving up and down or is turned upside down while swimming, then there is something wrong. The fish is stressed because of poor water quality or maybe the tank is too small for the fish which is affecting the swimming pattern.
  • Hiding: The disturbed swordtail tends to hide inside the plants or moves to the bottom of the aquarium.
  • Weight loss: If your swordtail rejects the food, it is because of stress. The affected fish will lose weight rapidly and die soon.
  • Over-crowding: If the tank space is small and the swordtails cannot move freely inside it, then they could get stressed. Too much fish in a small tank is very harmful to their health. Consider getting an appropriate-sized tank for swordtail to keep them stress-free.

Toxic water

The aquarium water is very sensitive to external factors. Even a little mistake can spread the toxicity. For example, if the tank water comes in contact with perfume, soap, hand lotion or any other chemical material, then the water becomes contaminated. In that case, the fish will get sick if the water is not cycled. You should take care before putting your hand inside the aquarium. Wear gloves or wash your hands with anti-bacterial handwash before adding food to the tank. These small precautions can save your fish from the dangers of toxic water.

Ammonia poisoning

The elimination of waste materials from a fish body (ammonia) takes place inside the tank water. The accumulation of ammonia waste makes the water poisonous which often becomes the cause of your swordtail’s death. You can decrease the level of ammonia by changing the tank water regularly and installing a good filtration system.

Also, check the nitrate and ammonia level of the tank water regularly. The ideal tank temperature for healthy living of swordtails is 72-78 °F, while the pH level must be between 6.8 to 7.8


If the swordtail is overfed by the owner several times in a row, it can disturb its health system. Some beginner aquarists do not know about the right quantity of food for fish so they end up feeding them more than the required amount.

To avoid the overfeeding you should follow the instruction mentioned on the food box and eliminate the excess food when the swordtail is done eating. If you won’t remove the food particles then they would start decaying inside the water and produce harmful toxins.


The swordtail can also die of sickness. The symptoms of various diseases among swordtails are mentioned earlier in this article. If you notice any symptom of sickness, then you should immediately consult an expert to treat them. Keep in mind that previously healthy swordtail fish can fight off the diseases while a stressed swordtail can die of the same disease. So, try to keep the fish stress-free.

It is also suggested to place the sick fish into a separate tank, otherwise, the disease can pass onto other fish that inhabit the same aquarium.

Killing beneficial bacteria

The presence of beneficial bacteria inside the aquarium is essential as they feed on toxins and wastes which make the swordtails sick.

Excess chlorine kills the beneficial bacteria, so it is necessary to add dechlorinator (aquarium salt) during the water change.

How to save the swordtails from dying?

If you don’t want your swordtails to leave you so soon then:

  • Maintain the water quality
  • Install an automatic filtration system
  • Give them an adequate amount of food
  • Do not overcrowd the tank

Related questions

Why did all of my swordtails die after a tank change? Due to a drastic change in water conditions, the fish can become stressed which might kill them. Before placing the fish into a new tank, make sure that the new tank conditions (temperature, pH level, aquarium salt, and filtration) are accurate and ammonia or nitrate level is properly balanced.

How to take care of a pregnant swordtail? A swordtail stays pregnant for almost 28 days, but if the mother is stressed or the water conditions are not adequate, then the gestation period may vary. In order to take proper care of a pregnant fish, you can keep it in a separate tank during the last few days of its pregnancy. Although, beware that If you keep the mother in a separate tank or a breeding trap, it might end up being stressed which might cause abortion or premature birth.


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