Swordtail Fish: A Complete Guide For Caring And Breeding

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  • Scientific nameXiphophorus hellerii
  • Family: Poeciliidae
  • Common name: Green Swordtail, Swordtail fish
  • Length: 5.5-6.3 inches (14.0 - 16.0 cm)
  • Activity: all level of the aquarium
  • Care level: very easy
  • Lifespan: 3-5 years
  • Tank size: at least a 30 gallon fish tank
  • Stocking ratio: 1 male x 3 females
  • Temperature: 70 -78 °F (21.1-25.6 °C)
  • Optimal pH: pH 7.0-8.3
  • Water hardness: 10-15 dGH
  • Lighting: Medium
  • Filtration: Medium
  • Aeration: Medium

About Swordtail fish

Male Swordtail. Image from Wikipedia.org.

Came from Central America, Swordtails are also well-known for another aspect among aquarists. They are livebearers and give birth to live fish fry instead of laying eggs. This act of giving birth to live fry is a wonder to watch and amazes both aquarists and the layman observer alike. Besides the beautiful sword-like tails, Swordtail fish are also popular aquarium fish for this reason.

Green Swordtail

The original variety known as the Green swordtail is olive-green on the upper-side of the body with the sides being yellow-green highlighted by dark-brown edges, which under certain light conditions is stunning.

Many other variations are also available:

  • The orange Swordtail is by far the most common domesticated variety.
  • Dark orange varieties are often sold as red Swordtails.
  • The pineapple Swordtail displays several shades of orange moving toward yellow down the body.
  • Black swords are black and may have metallic blue spots.
  • Tuxedo Swordtails
  • Combinations of all these colors have also been produced.

Swordtails are closely related to the southern Platy fish (X. maculatus) and can interbreed with it. Actually, many varieties or the Swordtail are from interbreed with X. maculatus.

Because Swordtail fish are hardy, they become a nuisance species in many of its non-native countries. Their populations have been established in regions of South Africa as well as along the east coast of Australia. It is not known where these feral populations came from, but they are likely to have been a result of aquarium Swordtails being released into the wild after their owners have gotten tired of keeping fish.

Today, Swordtail fish remain as one of the most popular tropical aquarium fish. Numerous inbreeding for color perfection have reduced the vigor of Swordtail fish, but more recently, the wild-type Swordtail has seen a resurgence in aquarium tanks for their ability to survive well in community tanks.

Fish tank setup and stocking

Being strong swimmers, Swordtails need a fairly large aquarium tank relative to their size (5-6 inches long when maturing). On the average, it is recommended that you have approximately 10 gallons of tank capacity for every Swordtail. The ideal aquarium should have plenty of swimming spaces and lots of plants. The tank should acquire a hood to prevent the fish from jumping out and death.

There is no limit on how many Swordtail fish you can keep in the same tank as long as you can afford a large enough tank size to house all your Swordtail fish comfortably. But male Swordtail fish can be territorial and will fight other males in the tank. Therefore you shouldn't keep a tank full of male Swordtail fish, no matter how beautiful they might look.

In fact, you should keep males to female Swordtail fish in a ratio of 1 to 3. Males are known to harass females, so you should have more females than males to keep them from being stressed out. You should set up your aquarium with plants and other covers for females to hide from males and also for males to hide from each other. But be careful not to use too many driftwood in your tank as they can cause your water to turn acidic. Swordtail fish prefer brackish water conditions at between pH 7 to 8.

Best fish foods for Swordtails

A basic question that many aquarists overlook when rearing fish is diet. Do you really know what goes into the fish food you are feeding your swordtail fish?

Like most small tropical freshwater fish, Swordtail fish will take well to a diet solely consisting of tropical flakes or pellets, and unfortunately, that is what most Swordtail fish are fed in homes. Simple logic will suggest to you that a varied diet will do wonders for your Swordtail fish development.

A favorite supplement for Swordtails is bloodworms, they are very rich in protein and contain healthy fatty acids like omega 6. But most importantly, bloodworms can enhance the color of fish with their pigments and are a staple of any tropical fish diet, including Swordtail fish. There is another fish food known as freeze-dried bloodworms which are also commonly used as a form of inexpensive substitute for bloodworms. You can also feed your fish with mosquito larvae. Mosquito larvae have similar qualities to real blood worms but are much less nutritious.

A little vegetarian diet is also a good idea for your Swordtail fish. You can feed it frozen spinach, zucchini or even bananas. Brine shrimp is another good supplement that you should consider adding to the diet of your Swordtail fish.

When choosing fish food for your swordtail fish, you need to consider if they float or sink. And if they sink, how quickly do they sink. Swordtail fish do eat food in any part of the tank but they are mainly mid tank feeders.

Food floating at the top of the tank will rarely be snatched, and similarly, food that sinks too quickly to the tank bottom will remain there for a while. And just because the food stays uneaten, it doesn't mean that your Swordtails is full.

How to properly feed Swordtail fish?

In general, you should feed your Swordtail fish twice a day with small pinches of food that sink slowly. Feeding them in small quantities will allow your fish to eat up all the food in the tank. It also gives you the chance to observe them while they feed. Fish that appear to be lethargic during feeding times maybe suffering from illness and you should check out their condition right away.

Continue to feed your swordtail fish in small pinches until they start to feed slowly like they are interested in the food. Food left in the tank will decay over time and pollute your water. If there is uneaten food in your tank, do remove them with a net to avoid spreading diseases in the tank.

One way to clear up food that is left on the bottom after feeding is to include some bottom feeding fish in your tank. Miniature catfish are perfect for this. They will help to keep the bottom of your tank free of food scraps.

Swordtail fish do not need to eat every day, but there is no reason not to if you are able to do so. While Swordtail fish are able to go without food for one or two days, regular feeding provides for the best health and allows your Swordtail fish to live longer.

How to breed Swordtail fish?

Like most other fish, the Swordtail fish breed only under the right water conditions. No fish will risk wasting precious resources by having young in suboptimal conditions for the fry to survive. Suitable aquarium breeding conditions are when the environment is best suited for your Swordtail fish to live in.

Typically, Swordtail fish survive well in brackish water with pH ranging from 6.8 to 7.8. While the adults can survive in a broad range of pH, fish fry are much more vulnerable and survive in more stringent conditions. That is why Swordtail fish must be provided with the best possible environment before they will start to breed.

Breeding can be encouraged by raising water temperature up by one or two degrees, to between 25 and 27 degree Celsius. Warmer water suggests a more plentiful environment, therefore, making it the right opportunity to breed.

Male (above) and female (below) Swordtails

Male Swordtails are, of course, required to mate with female Swordtails for breeding. Male Swordtails are known to pester females even when they are pregnant, this can cause stress for the pregnant. It is important to set up your aquarium with lots of cover and hiding places using plants. This allows the females to hide away from the males and also provides hiding places for newborn fry when the females give birth.

When a female Swordtail fish becomes pregnant, dark spots will begin to appear around her anus region. These spots are actually the eyes of fish fry showing through her scales. Her belly will start to bloat and eventually when it appears as if her belly will explode; it means she is ready to give birth anytime.


You can either choose to place her in a separate nursing tank for her to give birth, or you can let her give birth in the main tank with other Swordtail fish or even other species of fish around. If you do put her in a nursing tank, make sure that the water in the nursing is well cycled and does not contain high levels of ammonia content. Baby Swordtails are very vulnerable at birth and can quickly die from poor water conditions.

A problem with not placing Swordtail fry into a nursing tank is feeding them. They need to be fed and they will have to contend with other adult fish for any food that you put in the tank. Swordtail fry feed spirulina algae and newly hatched brine shrimps. The spirulina is very nutritious and will make the fry grow quickly while brine shrimp will help the near transparent fish fry gain their colors sooner.

Some owners prefer to let the fish fry try and survive on their own in the larger tank. In a sense, this is a selection process where only the fittest Swordtail fish fry will survive. But of course, you must also provide hiding places in the tank for the fish fry to stand a chance. If not, no fish fry will survive no matter how fit they are.

Common diseases and treatment

Swordtail fish are tolerant towards a wide range of water quality and are usually the last fish to die in a polluted tank. However, Swordtail fish can still fall sick when their immunity is weakened from stress. Stress in Swordtail fish can be caused by poor diet, overcrowding, and also poor water conditions. The best treatment for Swordtail fish diseases is to avoid them altogether by reducing any stress factors in the tank.

Because Swordtail fish rarely fall sick and when they do, it means that conditions are fairly serious and the fish can die quickly from condition if left untreated.

The best time to observe your Swordtail fish is during feeding. Watch out for fish that are lying at the bottom of the tank or hiding during feeding. Fish that are inactive during feeding are likely to be down with bacterial infection. If the Swordtail fish is infected with a parasite, the parasite is very likely to be found on the exterior of the skin. The fish will be irritated by the parasite and you can identify sicking fish rubbing its skin against the tank or decorations in the aquarium.

Here's a list of common bacterial and parasitic infections found in Swordtail fish.

Bacterial fin rot

The fish will have damaged fins that are torn or frayed and may have a white colored lining along its edges. Most people mistake this for injuries caused by bites from other fish, but fin rot can occur with any fights between the fish.

Body fungus

This is commonly known as the mouth fungus since the first sign of the disease is usually cotton like growth around the mouth region. This growth can spread to the outer edges of the fins or body of the infected fish.

Gill and skin flukes

These flukes are worm-like parasites that attack the gills and skin of the infected fish. The fish will have difficulty breathing and can be seen hanging out at the surface of the water.

White spot or ich

The most commonly seen disease infecting swordtail fish after body fungus, Ich appears as tiny white spots on the body of the fish. The infected fish will swim quickly around the tank as if a person has ants crawling on his body. It will also scratch against surfaces inside the aquarium.

These common diseases can be treated by medication available from your local fish store, but you must be able to identify them correctly and early to be able to administer the proper treatment.

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2 thoughts on “Swordtail Fish: A Complete Guide For Caring And Breeding”

  1. I have a Mail and a Female Swordtail in my Community Freshwater Tank. The Male knocked up the Female and she gave Birth without me even knowing about it. One day I happened to look in the Tank and saw a Baby hanging out near the surface by the Filter. So I assume there were more of them but I guess they got eaten by the rest of the Fish. I took the 1 Survivor and placed him in his own 10 Gallon Tank until he was Large enough to go back in to the Big Community Tank and Not be eaten. Sadly now that he is more grown up and his long tail grew out his Dad has been Bullying him. I thought the Parents would be happy to be Reunited with their Son but Mom ignores him and Dad actively seeks him out and Attacks him sometimes. Does Dad Not Realize it’s his Kid ? Or does Dad Not care and just because his Kid is a Male as well he will continue to Bully him ? I don’t know what to do now ? Do I have No choice but to remove one of them to Stop this fighting ? The Son doesn’t seek out his Dad to Fight him. It’s only the Dad who is acting like an Ass. I’m afraid he might end up seriously Hurting his Son. How do I Stop this Bullying Behavior from Dad Swordtail ?

  2. I would put the dad in a breeder box for a few days by himself it works for me, idk if it works for other tho, I had to do the same with two males that were brothers it worked really good for me at least, I hope you find a way.


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