Why is my Swordtail Fish Hiding?

Swordtail fish are an amazing addition to any tank; colorful, easy to breed and relatively peaceful. But sometimes, these fish can exhibit unusual behavior that’s difficult to understand, most commonly, hiding in the tank.

So, what causes swordtails to hide? Swordtails will hide when there is an issue in the water, when they are ill, during breeding or because they are genuinely scared.

Why Fish Hide and What To Do About It (Video)

So, how do you track down the main cause of your swordtail fish going into hiding? We will look into each of these interruptions in detail to figure out exactly what is causing your swordtails to show this type of conduct.

Water quality

Perhaps the first things you should look into immediately after this kind of behavior is the water quality. Swordtails usually require water of around 7-8 pH and a temperature of around 72°F- 78°F in order to survive comfortably. Alteration in these conditions could stress out the fish and could make them want to go into hiding.

More importantly, if the water quality of your tank differs from that of the pet store’s tank, this could cause the fish to stress out as well due to the sudden change in their atmosphere. A simple way to avoid these problems is to maintain the water quality along with regular filtration so the water doesn’t cause the fish to get confused and as a result, hide.


If water quality is not the issue for the fish, the second most important thing you should look into is whether your swordtail fish are sick or not. Tropical fish like swordtails can suffer from a number of diseases and illnesses, and some require a watchful eye in order to spot it out. Something you should always look for in your fish’s behavior apart from the hiding, is whether the fish is showing any white spot on its body or mouth. Other signs like improper breathing or bruises on the swordtail’s body can indicate some persisting health issue.

Most of these symptoms indicate a serious disease and the fish should get treatment soon so it can recover quickly. If by now you are sure that your fish is sick, make sure to add some bath salts to the water or any anti-bacterial medication (prescribed by an expert) to treat the illness.

If, however, you notice that the swordtail fish is looking too sick, is displaying very unusual behavior and shows no signs of recovery, your best bet is to shift that sick swordtail to another tank to die. This is due to two reasons:

  • A sick fish will contaminate the tank water and may pass on the disease to its other tank mates and cause the illness to spread throughout.
  • In case the fish dies within the tank, the same contamination will occur and it will require water change in order to clear the water.


If you still find none of the above causing the swordtails to hide, then your fish might simply be pregnant. This can quite easily be spotted as the swordtail fish’s belly will be clearly swollen and it will have a gravid spot which is a pretty straightforward sign of pregnancy. In this case, the hiding behavior is normal and you shouldn’t be too worried. Near the time of birth, the female swordtail fish will act territorial, and as a result, hide in the plants or any other decorations to protect its fry.

Once the swordtail gives birth, it should return back to its normal behavior. In order to protect its fry, make sure you transfer them to another tank or use breeding traps to contain the adult swordtails as they are prone to eating their own babies (fry).

Fear of other fish

If your swordtail fish are free from all of the above, then your fish might be scared or just simply be shy. Usually, swordtails are counted among the larger live-bearers and are not intimidated by other fish easily.

However, if you do have other larger fish or more male swordtails, they might be scared of the others or may be scared of the aggressive behavior of the other males. This will cause them to hide out of fear.

Some friendly tank mates for swordtail fish are mollies, platy fish, angelfish and guppy for beginners. These are fish with peaceful temperaments and will very rarely fight with each other.

External factors

The swordtails might also be afraid if their tank is inside a busy room with flashy lights or predators like cats. This could cause them to stress out and hide as well. Remove any disturbing factors near the tank to avoid the swordtails from getting scared.

Perfect tank conditions for swordtails

Water, obviously, is the most important factor that determines your swordtail fish’s health. With water being such a crucial factor in determining your fish’s survival, it must be matched exactly to their requirement to ensure their well-being. So, what are the perfect water specifications for swordtails?

Swordtails and other live-bearing fish like the Platy prefer a water pH of around 7-8, which is slightly alkaline. Swordtails are relatively large fish so you should confirm that the tank size you’re keeping for them is of a water capacity of 10 gallons or more for 2-3 swordtails.

The ideal water temperature for swordtails ranges anywhere from 72°F- 78°F (22 to 26 °С). All of this along with a filtration system and a weekly water change of 25% will ensure that you have healthy swordtail fish.

As for the tank decorations, keep some dense plants at the bottom to allow the juveniles to stay safe from predatory adults.

How compatible are swordtails with others?

Swordtails are a rather calm and peaceful fish and will not display aggressive behavior. They can quite easily live with other live-bearing fish like guppy and platy, too. But if you do plan to buy any swordtails, make sure you buy one male for at least 3 females.

Usually, when you keep more than one male swordtail, this will cause them to show aggression towards each other. They may fight and injure each other and sometimes, the stress will cause the weaker male to die. Also, the fish might overbreed as one female can produce anywhere from 15 to 100 fry and quite easily cause space to run out.

One thing you must avoid when keeping swordtails is to ensure that there are no predatory fish or fish larger than the swordtail itself. These fish would not make for some good tankmates for swordtails. More so, adult swordtails will feed on the baby fry as they have no maternal instincts. The decorations in your tank along with plants provide shelter to the fish’s newborns.

Related Questions

How big can swordtail get? It’s quite common for swordtail fish to grow up to 15cm or more. Females are only a margin smaller than their male counterparts.

Do swordtail eat their juveniles? The male fish will quite often eat the juveniles. If you have plants or other decoration, the juveniles will hide within them. You should still transfer them to another tank to keep them safe.

How often do Swordtail fish reproduce? Swordtail females will give birth every 4-6 weeks to anywhere from 15-100 juveniles at a time. They are livebearers, means they will give birth to swimming juveniles rather than giving eggs.


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