Swordtail Fish Care Guide: Lifespan, Feeding, Algae Eating, Size..


Swordtail (Xiphophorus helleri) is a species of the viviparous toothcarps. They are very lively and floating joyful fish. Swordtails are very closely related to the popular guppies, Mollys and platys. With platys, swordtails can even produce fertile offspring. The swordtail is a beautiful and adaptable fish that is perfect for medium-sized community aquariums. In this guide, you will learn everything about keepingfeeding, the right aquarium and breeding of swordtails.

Interesting facts about the swordtail

Profile: swordtail

Knowledge Surname:Xiphophorus helleri
Family:viviparous toothcarps
Origin:Central America
Size:10 centimeters
Life expectancy:5 years
Temperature:22 – 28 ° C,
PH value:6.5 – 8.5
Total hardness:10 – 30 ° dGH
Tank size:from 100 cm, 160 liters


Due to the large distribution area, the variability is relatively high. Some wild forms reach a length of 12 cm (males, without sword) to 14 cm (females), others only 9 or 11 cm. The sword can be up to 2/3 of the body length.


The natural forms’ colour is greenish with a metallic sheen and a clear vertical stripe from the eye to the top of the black-rimmed sword. Special wild forms can also be yellowish or bluish. The first cultivated form – after crossing the wild form of platy and swordtail – was red. In the meantime, there are offspring in many colours, from albino to gold, pineapple, neon and many others.


Originally swordtail fishes only occur from Mexico (south of Xalapa) to northwestern Honduras in waters that flow to the Atlantic. However, due to the release of aquarium fish, swordtails can now be found on all continents. However, in Europe, they only occur in warm waters (Hungary, Margaret Island in Budapest, around Heviz).

Gender differences

Like all males of the viviparous toothcarps, the male swordtail also has an anal fin, the gonopodium, transformed into a mating organ. The sword-shaped extension of the caudal fin is more striking. There are, however, two types of males: One in which the sword develops early and remains smaller (early males), and another in which the fish look like females for a long time, but become larger and get a long sword (late males). Real females have a small, dark spot in the anus area (pregnancy spot) and are noticeably fuller.


Unlike most other fish, swordtail fishes do not spawn. They give birth to fully viable young fish, which is why successful reproduction is possible even for inexperienced aquarists. When mating, the male inserts his gonopodium into the female’s genital opening and fertilizes it. After a gestation period of 28-42 days, the female gives birth to between 20 and 150 live young. The female can become pregnant again immediately after birth. In theory, a female could give birth to up to 150 animals every 30 days.

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The young fish have a rather poor chance of survival in community tanks. In order to increase the success rate of the breeding, the young fish should be kept in a separate breeding tank. Artemia and small crumbled dry food are suitable as food for young fish.

Life expectancy

swordtail fishes have a life expectancy of up to a maximum of five years. But three to four years are still quite normal.

Interesting facts about posture – swordtail fish


swordtail fishes are typical omnivores that can even be kept with a pure dry food diet. But they also like to take frozen and live food, which should be served once a week.


Group size

Swordtail males can be extremely aggressive towards one another. Two or three males can fight one another so hard that only one male remains. If the aquarium is sufficiently large (from 300 L), five or more males of the same size can be kept so that the aggressions are evenly distributed. The females should always be somewhat in the majority because the males’ courtship can be very violent.

Aquarium size

Due to the achievable maximum length and the very impetuous and expansive courtship behaviour, the aquarium should have an edge length of at least 100 cm (from 160 L). There a male can be kept together with several females.

Tank Condition – swordtail fish

In nature, many bodies of water have only a few plants. Nevertheless, they should not be missing in the aquarium as they also contribute to water maintenance. Some denser plant populations also allow the females to retreat a little if they are too pressured, and young animals to find protection from their parents who are following them.

Swordtail Tank mates

Swordtails are good for socialization. Male swordtail fishes are aggressive and intrusive toward other species. If the ratio between male and female swordtails is right (approx. 1: 3), the males are usually not interested in other species and leave them alone. Other species of viviparous toothcarps such as guppies or Mollys are ideal. Socialization with platys is not recommended, as swordtails and platys can produce less beautiful swords than genuine swordtail fishes.

Possible ways of socialization

Water values

swordtail fishes are quite robust in terms of water values. In terms of temperature, acidity (pH value) and total hardness, the swordtail has a large tolerance range, which is why it is well suited for beginners and forgives one or the other inattentiveness.

  • Water temperature: 22 – 28 ° C
  • pH value:  6.5 – 8.5
  • Total hardness:  10 – 30 °

Development of sexual characteristics

A peculiarity of the swordtail is that they are visually born as females. As a small fry, they all look the same. It is not until puberty that it becomes clear whether they develop into fertile females or whether their sexual characteristics develop as males. However, they do not become sexually mature late males until they have lived together with sexually mature females for some time. When it comes to mating and the young are born, the parents are happy to eat them up again. If you want to enjoy your offspring in the long term, you should therefore place them in a special rearing tank.

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Swordtail breeding and breeding

How do you know that swordtails are pregnant?

In pregnant swordtails, the belly is thick. The belly will slowly become thicker within 1 to 2 weeks. Otherwise, there are other causes, e.g. B. a full stomach. In the rear area, the abdomen usually becomes a little darker. The darkening of green Xiphophorus can be seen particularly well.

How long swordtails are pregnant

The gestation period depends on water temperature and food. At a temperature of around 28 ° C and good live food, the gestation period is a little shorter.

If the gestation spot is very dark, the birth is imminent. The gestation spot is small in front of the female’s anal fin.

(Xiphophorus helleri

Raising young fish

Special measures for breeding and rearing are not required. However, the parents eat their own young. Hiding places for the young are provided by floating plants such as pond liver moss (Riccia),  hornwort and Naja.

These plants do not take away as much light as, e.g. B. Shell flowers. In an aquarium set up in this way, some robust offspring will always come through. Even so, depending on the population, 20 young animals can survive. After about four weeks, the young move around the whole aquarium.

The temperature should be 22 – 24 ° C. Rearing is possible in the community tank if the inmates are not chasing too hard.

If a particularly large number of offspring is desired, it is advisable to move the young as soon as possible after birth in a spawning box or a separate rearing tank. Spawning boxes are too small for the dams. The stress this creates can result in the mother having undeveloped or dead cubs.

The young are also quickly eaten by the mother if the box does not have a partition.

For the first two weeks, the young can be fed with finely ground flake food and freshly hatched  Artemia nauplii. Food in tablet form, which slowly dissolves, can also be placed near the young animal hiding places.

In addition, plant-based food can be fed, e.g. B. canned carrots, cucumber, lettuce or simply vegetable, green flake food. Green algae in the aquarium are also eaten. If there is sludge, the young will find diatoms there as food. It is fed so much in the morning, at noon and in the evening that all of the food is eaten every 2 to 3 minutes.

After two weeks, the cubs eat frozen food like red mosquito larvae.

It should be fed often, and the water changed accordingly, as with all other juvenile fish.

When the young get colour, they can be released from the spawning box or breeding tank. They are then around 3 to 4 weeks old, around 1.5 cm long and slightly thicker. As a rule, they are then no longer eaten by adult swordtails.

Normal swordtails mate with swordtails that have other fin shapes. In the case of Lyratail swordtails, this is even necessary to have offspring. Lyretail males have an extremely elongated gonopodium, which usually makes mating impossible.

Sufficient space to feel good

When it comes to aquarium setup and feed choices, swordtails are not particularly demanding. Above all, you need one thing: lots of space! The hard-working swimmers are anything but frugal and defend their territory vigorously. The males, in particular, are sometimes aggressive towards conspecifics or relatives such as the platy. A prerequisite for the socialization of several schools with one another or with cichlids is, therefore, a sufficiently large tank that can be divided into several areas. To prevent the sporty fish from jumping out of the aquarium, it should also be secured with a washer.

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Can swordtails change their gender?

Most reports of sex changes in swordtails are likely based on inaccurate observations in premature males.

However, there is a study from 1926 in which 2 cases of sex reassignment in sword-bearers are described:

Biol Bull 51:

98-111, August 1926, Marine Biological Laboratory Complete Sex-Reversal in the Viviparous Teleost Xiphophorus Helleri

JM Essenberg

Anatomy Laboratory, School of Medicine, University of Oklahoma

  • Two cases of complete sex change from female to male in adult swordtails are described.
  • Both animals had normal pups prior to sex reassignment.
  • Both animals fertilized virgin females who then had normal young.
  • After the conversion, the two animals could not be distinguished from normal males; only the body shapes were female.

A gender reassignment report was sent by email from RS: He originally bought a male and two female swordtails.

The females have since spawned several times.

After about 3/4 year there are now three large males and many small swordtails in the aquarium.

So two of the original females have transformed into males.

 Hardened spawning in swordtail fishes

In females that are kept without males, spawn hardening can occur. Therefore, a male should always be kept.

In all viviparous fish species, the young develop in the egg in the womb, just as in all other fish. Up to birth, all processes proceed like with other fish. Only at birth do the young hatch from the egg and leave the womb at the same time.

Only for Mexican highland pennies, e.g. B. the knight’s carp and the banded carp, the young leave the eggshell in the womb. They are then real fish and are nourished on nutrient cords, so-called trophotaenia.

How old do swordtail fishes get?

Swordtails live to be around three years old. The animals in the trade are around 6 to 12 months old. A swordtail that was bought in an aquarium store and swam in its own tank for two years is very old.