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How to Breed Swordtail Fish in Your Own Aquarium

Swordtail fish are one of the most effortless fish to care for in a home aquarium. They have a pleasant demeanor towards other small fish and are vibrant in color as well. It is no wonder why a person would want to breed these fish and here is how to do it!

Quick Answer

Breeding swordtail fish entails putting a male and female (or multiple females) into a separate tank and letting them get to work! Swordtail fish are one of the easiest fish to breed in an aquarium with no extra work involved. They are livebearers, which means no eggs, and are always ready to mate. 

Despite swordtail fish being easy to breed, there are a few things to know prior to beginning the breeding journey. 

How long does it take to breed swordtails?

Swordtails are extremely easy to breed due to the fact that they are always ready to mate, as long as the tank parameters are set correctly and checked on. If the numbers are right, they may begin breeding within a few days of being placed in the tank, or even sooner.  

Below are a few parameters to watch out for to get fry as quickly as possible:

  • Temperature:  Between 65°-82°, but preferably 78°F
  • Water Hardness: 12-30 dGH
  • pH: 7.0-8.4

Since swordtails breed so easily, you should have at least a 20 gallon tank to accommodate the adults and fry. As stated, the females can become pregnant every 28 days and have up to 100 fry per time. 

Red Swordtail Xiphophorus hellerii fish

How many swordtails should be kept together?

Swordtails should be kept in sets of 3-4 females per 1 male. This will help overbreeding on any one female and keep any fights to a minimum. 

With that being said, swordtails generally have a very pleasant demeanor and can be housed with other species of fish as well (even if you are trying to breed). The following are just a few of the cohabitants that can be housed with swordtails:

  1. Platies 
  2. Mollies
  3. Angelfish 
  4. Cory Catfish 
  5. Tetras

The above fish are all around the same size as a swordtail so would cause no imminent danger to them. Swordtails are not aggressors and should not be housed with larger fish, such as cichlids that are very territorial. This match could end up killing the swordtails, especially when breeding. 

How to tell if your swordtails are mating?

Swordtails are a popular aquarium fish, and it’s easy to tell when they’re mating – they’ll side by side, giving each other a clear view of their dorsal (back) fins. In fact, this behavior is so common that it’s often called the “side-by-side mating display.”

This display is a signal to other swordtails that the two fish are ready to mate, and it’s usually accompanied by courtship behavior such as flashing their gills and vibrating their bodies. Another sign is catching your fish nudging the rocks with their tail up.

Two Swordtail fish swimming together in an aquarium

How to tell if a swordtail is pregnant?

Swordtails are tropical fish, and as such, they’re naturally reproductive. That means they’ll become pregnant and give birth to live young pretty much any time of the year. But there are some telltale signs that a swordtail is pregnant, so you can make sure you don’t accidentally raise a bunch of babies without knowing it.

One of the more immediate tell-tale signs that a swordtail in your tank is pregnant is an enlarged belly. The female’s belly will become larger as her pregnancy progresses and end after around 28 days. 

A few other signs that a female could be pregnant is if you notice an increased appetite, being more aggressive towards other fish than usual, or hiding from males in other parts of the tank. 

How long are swordtails pregnant for?

The gestation period for a swordtail is 28 days. As opposed to other species of fish, swordtails are livebearers. This means that rather than laying eggs, they give birth to live fry (baby fish).

Swordtails can also get pregnant again within a few days of just having their fry! This means they can have about 100 fry (some batches are much smaller), 12 times a year. 

This makes it extremely important to have a plan in place on what to do with the fry. Some will sell to pet shops, get a few more aquariums, or give them away.

Do swordtails give birth all at once?

Female swordtails typically give birth to all of their fry at once. As mentioned, they can lay around 100 fry per pregnancy. With this being said, on occasion it may take a bit longer for the female to give birth depending on how many fry she has, and if there are other fish in the tank that could cause distress. 

Will swordtails eat their own fry?

As it turns out, swordtails are among the few fish that are known to eat their young. This behavior is typically used as a form of defense – by eating their young, the swordtails are able to protect them from predators. Backwards thinking, I know, but while these fish are sweet-natured, they are not exactly maternal. 

This behavior is also used as a means of survival. By eating their young, the swordtails are able to gain the nutrients they need to survive and grow. In fact, this practice is so common among swordtails that it has even been studied and documented. 

How do you keep swordtail fry alive? 

Once fry are born, it is recommended to keep them in a separate tank than the adults. This will prevent them from being eaten. You should also have food ready for them as soon as they are born. 

While swordtails can eat the flakes found at your local store, it is recommended that fry eat a more wholesome food such as newly-hatched brine shrimp. The advantage to using baby shrimp is that they can also clean the tank. Feeding shrimp also inhibits their growth a bit faster than flakes would.

Another important aspect of keeping fry alive are the tank conditions. The following number are what is needed in order to ensure proper growth in your new additions:

  • Temperature: 64-83 degrees
  • pH: 7.00-8.3
  • Water Hardness: 12-30 KH

These numbers are the same as adult swordtails, but you will want to keep the tank on the warmer side of the spectrum. In addition, if the tank is even slightly off of these numbers, it can inhibit the growth of the fish. 

Looking for more information on aquarium fish?

In that case, make sure to check out our aquatic fish page. There you’ll find everything you need to know about aquarium fish, shrimp & snails.

How fast do swordtail fry grow?

To reach full size, fry will have to grow for around six months in the proper water conditions in order to grow to their maximum size. The maximum size for a male swordtail is around 2 inches while a female will typically grow to 1.5 inches. 

So how exactly do you tell if you have male or female swordtails? The difference is in the tail! While the males are inherently longer, they will also have an elongated caudal appendage (the sword) beneath their tail. This is absent in females.

How long do swordtails live?

Once your fry are mature, you may be curious as to what the average life expectancy is. The answer is 3-5 years if your tank has the correct water conditions. Keep in mind that if you are keeping your swordtails this long, you will end up with thousands of fry. 

Make sure to rehome any males if you are overcrowded or rehome them! Overcrowding can also cause premature death in fish due to stress.