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Top: Male Black Swordtail facing right. Bottom: Female Black Swordtail facing left.
A male Black Swordtail facing right. He has a kink in his tail.
Two female Black Swordtails. The one on top is facing right, while the one on the bottom is facing right.

Black Swordtail

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Tank Level:


Minimum Tank Size:

20 Gallons




7.0 - 8.4

General water hardness:

12 - 30 dH


68 F to 80 F (20 C to 26 C)


Peaceful Community/Semi-Aggressive Community

The Swordtail (Xiphophorous hellerii) is a species of freshwater live-bearing fish, popular for the male’s long sword-like tail. These fish come in many different colour mutations, and with a variety of fin mutations. "Black Swordtails" have dark black bodies with shimmery blue-green scales. Listing is for mixed-sex swordtails that are fully grown.

From nose-to-tail, males generally reach 5 inches long, while females can grow up to 6 inches in length. These fish prefer water temperatures from the mid-60’s through the low-80’s, and do best in water that is very hard and slightly alkaline.

Because these fish can get quite large, it is recommended to keep a single swordtail in no less than 15 gallons of water. For every additional swordtail, add 5 gallons. Males can be aggressive towards one another, so it is recommended to only keep one male per every 15 gallons of water. Because these fish are livebearers, they should be kept in a female-to-male ratio of 3:1 (three females per every one male). Swordtails will live for 5 years on average.

While these fish are not particularly aggressive, they will lash out if space is not sufficient. Males can be aggressive towards one another if the tank is not large enough. In a big enough tank, swordtails are very docile and can be kept with almost any other peaceful community fish species.