Swordtail fish – is a bit quarrelsome fish

Swordtail (Xiphophorus hellerii) is one of the most famous and spread tank fishes. In general this fish is quite peaceful and it can inhabit in a common tank.

Though each Swordtail fish may have its own temper, which can be both timid and shy or aggressive and blusterous. This is especially true for males. They can be aggressive towards each other.

Habitat in the wild

Xiphophorus species inhabit in water basins of Central America. Mainly within areas adjacent to Atlantic coast – Mexico, Guatemala, Honduras. The fish is encountered both in mountain rivers with strong flow and in their lower reaches as well as in lakes, bogs and lagoons.

Swordtail fish prefers shallow, thickly planted areas, where they feed on various insects, algae and detritus.

Swordtail (Xiphophorus helleri) is from Poeciliidae family. Xiphophorus helleri is translated from Greek like «xiphos» – a sword, «phoros» – to carry. Prefix «Helleri» was added to the fish name by the name of German natural philosopher (Karl Bartholomä us Heller), who was the first to catch the fish in Mexican lakes and successfully brought it to Europe.

In 1848 the fish was first described by doctor Johan Hekel, a laboratory assistant at museum of natural history under Imperial Natural History Museum in Vienna.


Swordtail size may be quite large. Males may grow to be about 4 inches (11 cm) long. Females are about 5 inches long (12 cm) excluding the tail length.

However, the fish is smaller in tanks, which highly depends on tank conditions. Swordtail fish lifespan is about 3-5 years.

The fish body is elongated and flatted from sides. The feature of the fish is its unusual tail in a shape of sword, which actually gave the name to it.

The tail may be either rounded with one ray or it may have several rays.

As for the fish coloring, it difficult to select just one pattern, though red with black tail seems to be the most spread one. It’s quite a complicated task to describe all the species, since there is a large variety of its hybrids (koi swordtail, pineapple swordtail, neon swordtail).

Difficulties in keeping

This is one of the most popular fish for beginners. It’s not demanding, not very large, easy to breed.

As for demerits you may find – some males are bully, especially towards each other.

Keeping in the tank

Scientific NameXiphophorus hellerii
Common NameSwordtail fish
Tank size10 gallons and more
TemperamentAggressive to males
Temperature72°F- 78°F (22 to 26 °С)
Sizeabout 4 inches large (11 cm)

Swordtail fish care isn’t very difficult. Many beginners keep Swordtail in small tanks. However, this isn’t right. In fact, Swordtail is quite a large fish.

Therefore, I’d recommend a tank capacity starting from 10 US gallons (40 L) for Swordtail keeping. The larger, the better.

Remember, that for breeding you’ll need one male fish and 2-3 females. If there is just one male and a female, he’ll be haunting her all the time and she’ll be stressed, which may cause the fish death.

Try not to put several males into one tank, since they have strongly pronounced hierarchy. The male fish in charge will always be chasing other males and it is followed by fights, injuries, stress.

Swordtail fish is rather not demanding, if it comes to tank water temperature, the fish can live both at 65°F (18°С) and at 82°F (28°С). Perfect water temperature is in the range of 73°F – 79°F (23-25°С).

Such parameters as water hardness and рН aren’t very important for the fish, but it feels better in water with medium hardness and рН 6.8-7.8.

You can install water filter if you like, but water renew is a must – about 20% every week.

Keep in mind, that swordtail fish not only swims fast, it also jumps well. Therefore, at tank with the fish must be covered, otherwise you may find dead fish on the floor near the tank.

You can choose tank decorations at your discretion. The only thing is, that it should be thickly planted.

For the female fish it is easier to hide in plants from aggressive males and if she spawns the juveniles will not be eaten right away.


The fish is considered to be a peaceful one, but my experience shows that it’s not always true. They have very strong intrageneric aggression. Besides, old males may attack other fishes in a tank, but this depends on a specific fish temper.

Some fishes live peacefully and some of them become bully, start haunting young males and other fishes. Small tanks without plants encourage aggressive behavior of the fish.

What you definitely shouldn’t do, is to keep two or more males in one tank. This guarantees fights in the tank.

Though they will not kill each other, but constant stress leads to death of the weakest male fish. There are two ways how you can settle the issue: keep one male and 3-4 males in a tank or lots of males in a spacious tank with females.

This way there is no obvious leader between the fish and aggression in spread uniformly (not just one and the same fish suffers). As a rule, they tend to be neutral to their tank mates.

So, the best swordtail fish tank mate is fish of the same size, but not a predator one. This can be angelfish, kribensis, kuhli loach, emperor tetra.


You can feed it with artificial, live or frozen food. Like all other fishes swordtail fish diet should be diversified. It is especially important to provide it with vegetable food. The thing is, that in the wild major part of the fish diet consists of thin algae and other fouling.

To have such amount of algae in a tank is impossible, but you always can buy fish food flakes with vegetable supplements. You can make these flakes a basic component of the fish diet and add live food as a supplement.

If you (just like me) regularly feed your fish with artificial food, then the links will be very helpful for you – Hikari Fancy Guppy, API Fish Food Pellets, Fluval Bug Bites. I know what it’s like when you pet fish die because of low quality food or get ill due to infection ingress into the tank with live food. I myself give some of this food to my pets and as for the rest I’ve heard and read lots of good reviews. Yet, all of the food is of high quality and it is the best one for this fish kind as well as it keeps the tank water clean.


It is extremely easy to see between swordtail fish male and female. Only male fish has a sword on its tail. This is a long outgrowth due to which the fish got its name.

Just like all live-bearing fish the anal fin of the male fish has been modified into a tube (gonopodium) and the female fish has a wide anal fin.

Quite often it happens, that swordtail fish female suddenly has an outgrowth and becomes a male fish!

At that it behaves like a male fish, haunts other females, but it is sterile. What causes such phenomena is still unclear.


Swordtail fish is a live-bearing fish, that is its juveniles appear not as eggs, but as a completely formed small fish. The male fish fertilizes eggs inside the females body and she carries them till she is ready to spawn. Usually this period lasts for 28-30 days.

It is very easy to get swordtail fish juveniles, just like from other live-bearing fish (guppy, molly fish). The female fish can even spawn without the male, because she stores male milt inside her and can fertilize the eggs herself. Therefore, if the female fish spawned and there is no male fish in a tank, this is the case.

Swordtail fish becomes reproductive at the age of 5-6 month. For breeding (and also for the fish to feel comfortable) it’s recommend to keep the fish in ratio – 1 male for 3 females.

The easiest way to stimulate swordtail fish breeding is to raise the temperature of tank water. Ammonia and nitrates level should be as low as possible and рН 6.8-7.8. When the female fish becomes fatter watch the dark spot near her anal fin.

As the spot gets darker and the fish becomes significantly fat, the spawning will happen very soon. This dark spot is actually juveniles eyes which are seen through her body.

The female fish spawns from 15 to 100 and more juveniles at a time. Spawning usually occurs in the morning.

It seems to me, that the most important rule you should follow when breeding swordtail fish – its taking care of its juveniles. Unfortunately, parents eat their own offspring. Taking into account that swordtail fish juveniles are quite large and brightly colored – it looks like extermination.

In the wild swordtail fish never sees its offspring, since the juveniles go with the water flow right after they are born. In the tank parents take them for food.

To save the offspring the tank should be thickly planted. Plants are put on the tank bottom, in the water and they should be especially thick on the water surface.

This way you provide the juveniles with shelter from aggressive parents and most of juveniles survive.

Also to safe the offspring you may use a special depositing hopper – the female fish stays in it and the juveniles fall into a spawning tank after they are born. This way you prevent any contact between the offspring and its parents.

The third option to keep the juveniles safe is to remove their parents from the tank right after spawning. This is an easy way, but it in this case aquarist should be attentive and timely.

Swordtail fish juveniles are large, active and hungry. You can feed them with egg yolk, food for juveniles and brine shrimp nauplii. It’s desirable to add spirulina or flakes with vegetable supplements.

Provided with spirulina+live food diet the juveniles will grow fast and have bright coloring.

Last update on 2019-10-13 at 22:21 / Affiliate links / Images from Amazon Product Advertising API