Can Swordtail Fish Change Gender?

swordtail fish

Swordtail fish is one of the most beautiful fish you can choose to put in your aquarium. They make have a characteristic long tail spike which gives it the name swordtail. The sword in the fish is just for decoration, it doesn’t have any function whatsoever.

There different colours, shapes, and sizes of Swordtail fish are a result of decades of selective breedings. They come in a variety of colors like red, neon, marigold, black, and pineapple. The most popular colours are red, orange, and green. Irrespective of the colour or size, their sword is the same. It always has a black band along the edge.

The male is territorial and can be aggressive towards other males especially when there is a presence of a female specie. In every group of swordtail, there is always one dominant male.

There has been a lot of rumours online and among some hobbyist that female swordtail fish can change their gender. 

Can Swordtail Fish Change Gender?

The fact that the female swordfish can change her gender is just a rumour because it is not true. The reason why most people believe this rumour is because when there is a presence of a dominant male in a group of other male swordtail fish, the other fish will hold back with their development.

This is was gives them the appearance of a female. They stay that way for as long as the male dominant is alive. When he dies, a sub-dominant male matures quickly and this is what gives a lot of people the impression that the swordfish tail changes its gender.

All swordfish are either born male or female and they stay that way up until they die. None of the genders can change to the other.

How Does The Swordtail Fish Breed?

Your swordtails are livebearers. This simply means they give birth to live fish, and their babies swim freely and are independent of their parents right after birth. They are unlike the egg-laying fish who scatters their eggs for the male to fertilize them in water. 

Most live-bearers take 28-30 days to breed and it’s no different for the swordtail specie. The male swordtail I sent his Milt into the female swordtail and fertilizes her eggs. She holds these eggs in her body until they are fully developed then she gives birth to them.

How Many Male Swordtail Fish Can You Have In One Group?

Yes and no depending on how developed the male is. With the male swordtail fish being a territory, they can defend all the females and males in their territory. This makes them aggressive. To tone down the level of aggression between them, it is advisable to keep one male in a group of 4-5 female Swordtails.

If you are getting young swordtails, you can grow them to a point where you can sex them. Select a male who has started developing his sword and group him with 4-5 females. He will protect them and there will be less aggression because he is the only male in the group.

The remaining fish can be moved to another aquarium. You can keep them for breeding, and in no time they will grow into a larger family of Swordtails community.

Can You Have Only Males In A Group?

Knowing the fact that the male Swordtail can be aggressive, you might be wondering if there is a possibility of having just a male Swordtail in your aquarium if you don’t want them to breed. Most time the male becomes aggressive in the presence of a female.

If you are having just males and no single female, they are most likely going to coexist in harmony for a group of not more than 6-10. The larger the number the more chance of them being aggressive toward one another. To keep that low, you should have just a few numbers for a peaceful coexistence depending on the aggression level and personality of the fish. Each fish has a different personality and level of aggression. 

You can also have multiple males and females with a low level of aggression but you have to provide a larger aquarium that is heavily planted. Adding lots of decorations will also provide a hiding place for them. The females have to outnumber the male, having 2&3 females per male in a 50-gallon aquarium.

How Can You Sex Swordtail?

When sexing Swordtail, you look out for the dominant male. Finding it is easy because you will see a sword at the tail fin just as the name implies. The less-dominant male’s anal fin is pointed while that of the female is triangular in shape.

When the male matures and becomes dominant, the anal fin becomes long having a sword. This is known as a gonopodium. The male uses it to transfer Milt into the female for breeding. 

Difference Between Male And Female Swordtail Fish

If you don’t want your fish to breed, you should separate them because some of them can start reproducing as early as when they are 12 weeks old. To separate them, you have to know the difference between males and females. You can differentiate a male from a female by looking out for the following features.

  • The male Swordtail has a tall fin extension, this feature is unique to only them. The females have a round tail fin.
  • The females have a round and Fuller body and they become 1½ inch longer when they mature.

If you want to keep the male and female together for breeding, the number of females should be more than the male. You can keep 2-3 females per male fish because the male is always chasing the females for mating. Having more males than females will make the males more aggressive and in turn stress the females.


The female swordtail fish cannot change its gender, unlike what a lot of people believe to be true. As a result of the male swordtail being a territory, a single male dominates a group thereby making other males delay their development.

This makes a lot of people see them as females. When the dominant male dies or is moved from the group, a sub-dominant male develops his male characteristics and this gives people the impression that the female swordtail fish changed its gender to a male. All swordtails are born either male or female and they remain that way without changing gender because none of them can do so.

When next you notice the sword developing, this is just showing that that is the dominant male in the group who is protecting the females.

Written by Justin Michaels

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