Product Details

Black Marble Swordtail – Xiphophorus hellerii

The Black Marble Swordtail is a striking freshwater livebearer with bold black marbling, active swimming behaviour and the classic extended “sword” tail seen in mature males. This selectively bred form of Xiphophorus hellerii is a hardy and colourful choice for larger community aquariums, especially where the water is naturally alkaline and mineral-rich. It is peaceful to moderately lively, easy to feed and well suited to planted aquariums with open swimming space.

Key Identification:

Common Name: Black Marble Swordtail
Other Names: Marble Swordtail, Black Marbled Swordtail, Marbled Swordtail, Swordtail
Scientific Name: Xiphophorus hellerii
Strain / Form: Black Marble colour strain
Fish Type: Livebearer
Water Type: Freshwater

Natural Range & Habitat:

Xiphophorus hellerii is native to parts of Central America, where wild swordtails occur in freshwater streams, rivers, ditches and vegetated waterways. They are usually found in areas with plant growth, open swimming space and steady water movement.

The Black Marble Swordtail is a captive-bred aquarium strain rather than a wild colour form. In the aquarium, it does best in a planted setup with open swimming areas, gentle to moderate flow and cover from live plants, floating plants or décor.

Appearance & Adult Size:

Black Marble Swordtails show a variable marbled pattern of black, dark grey, pale, silver, orange, red or mixed tones depending on the strain and individual fish. Males develop the characteristic lower tail extension known as the sword, while females are usually larger-bodied and lack the sword.

Adults usually reach around 10–12 cm, with males appearing longer when the sword is included. Females can become noticeably fuller-bodied, especially when mature or carrying fry.

Aquarium Suitability:

This is a good choice for larger community aquariums with peaceful to moderately active fish. Swordtails are hardy, adaptable and usually confident once settled, but they are active swimmers and need more space than smaller livebearers such as guppies or Endler’s.

They are best kept in stable, well-filtered aquariums with hard, alkaline water. They are not ideal for very soft acidic aquariums, nano tanks or slow-moving setups with delicate timid fish.

Recommended Aquarium Size:

A practical minimum is 100 litres for a small group, with larger aquariums preferred for mixed communities or groups containing multiple males.

Keep in groups, ideally with either a male-only group or a ratio of one male to two or more females to reduce persistent male attention. If males are mixed, provide enough space and visual breaks to reduce chasing.

Water Conditions:

Temperature: 22–26°C
pH: 7.0–8.2
Hardness: Moderately hard to hard water preferred
Additional Notes: Stable mineral-rich water is important for long-term health. Avoid very soft acidic conditions, sudden temperature swings and poor water quality. Regular water changes and good filtration are recommended, as swordtails are active fish with a healthy appetite.

Temperament & Tank Mates:

Aquarium Category: Community Fish

Black Marble Swordtails are generally peaceful but lively. Males may chase females or display towards rival males, especially in smaller aquariums or groups with too few females.

Suitable tank mates include platies, mollies, guppies, rainbowfish, peaceful barbs, larger rasboras, danios, corydoras, bristlenose plecos and other hardy community fish that enjoy similar water conditions. Avoid very timid nano fish, long-finned slow swimmers, fin-nipping species, aggressive cichlids and soft-water specialists that prefer acidic conditions.

Feeding:

Black Marble Swordtails are omnivorous and easy to feed. Offer quality tropical flakes, small pellets and livebearer foods as the staple diet.

Supplement with spirulina flakes, algae-based foods, daphnia, brineshrimp, bloodworm, mosquito larvae and blanched vegetables such as courgette or spinach. A varied diet with some vegetable matter helps maintain condition, colour and digestion.

Behaviour in the Aquarium:

This is an active mid-to-upper level swimmer that spends much of the day exploring open areas, browsing plants and feeding eagerly. Males may display their swordtail and colours while interacting with females or other males.

Swordtails are livebearers, meaning females give birth to free-swimming fry rather than laying eggs. In planted aquariums, some fry may survive among dense plants, moss or floating cover, although adults and tank mates may eat young fry.

Care Notes:

Provide a secure lid, as swordtails are strong swimmers and may jump when startled. Maintain stable, clean, mineral-rich water and avoid overcrowding.

If breeding is not desired, consider keeping a male-only group or separating sexes. Females can store sperm and may continue producing fry after being separated from males. Different swordtail and platy strains can hybridise, so keep strains separate if maintaining a specific line or colour form is important.

Recommended For:

Beginner to intermediate freshwater aquarists

Availability:

Common / Captive-bred aquarium strain

Image Disclaimer:

All images are a visual representation of the fish you will receive, made to be as accurate as possible. Natural variation in size, black marbling, body colour, sword length, fin shape, sex and markings can occur between individual fish.