Black Marble Swordtail - Xiphophorus hellerii

Black Marble Swordtail (Xiphophorus hellerii)

The Black Marble Swordtail, Xiphophorus hellerii, is an attractive selectively bred livebearer recognised by its contrasting black marbled pattern across a lighter body, with mature males developing the characteristic elongated lower tail ray known as the sword. This ornamental strain shares the hardy nature and active swimming behaviour of the classic Green Swordtail, making it a popular choice for spacious freshwater community aquariums. Black Marble Swordtails are active omnivores that appreciate planted areas, open swimming room and moderately hard, alkaline water. Their easy breeding behaviour and striking individual colour variation make them particularly appealing to both beginner and experienced freshwater fishkeepers.

Common Name:
Black Marble Swordtail, Marble Swordtail, Black Marbled Swordtail, Black Marble Green Swordtail.

Scientific Name (Latin):
Xiphophorus hellerii

Maximum Size:
Males can reach approximately 14 cm in total length including the sword, while large females may reach approximately 16 cm.

Water Type:
Freshwater

Origin / Natural Habitat:
The Black Marble Swordtail is a selectively bred aquarium strain of Xiphophorus hellerii and does not occur naturally in this colour form.

Wild Green Swordtails originate from North and Central America, from Veracruz in Mexico southwards to north-western Honduras. They inhabit streams, rivers, warm springs, canals and ponds, often favouring areas containing dense aquatic vegetation.

Water Parameters:
Temperature: 22–28°C
pH Range: 7.0–8.0
Hardness or Salinity: Approximately 9–19°dGH; moderately hard to hard water is preferred.

Temperament:
Generally peaceful and suitable for active freshwater community aquariums. Males can become competitive with one another, particularly when females or limited territories are present.

Maintain either a single male or provide sufficient space and visual barriers when keeping several males. A ratio of approximately one male to two or three females helps reduce persistent courtship pressure on individual females.

Diet:
Omnivorous. In nature, Xiphophorus hellerii consumes plant material, small crustaceans, worms, insects and other available foods.

In the aquarium, offer high-quality tropical flakes or pellets as the staple diet, supplemented with spirulina, algae-based foods and occasional blanched vegetables.

Provide frozen or live foods such as Artemia, daphnia, mosquito larvae and small bloodworms for additional protein and variety. Feed moderate portions once or twice daily.

Minimum Tank Size:
A minimum aquarium volume of approximately 120 litres is recommended for a small group, with a long swimming area, planted sections and sufficient room for males to establish distance from one another.

Larger aquariums are preferable for breeding groups or when maintaining several adult males.

Behaviour & Activity:
An active, confident livebearer that spends most of its time swimming through the middle and upper areas of the aquarium.

Mature males develop the characteristic sword-shaped extension from the lower portion of the tail fin. Females lack the elongated sword and usually develop a deeper, heavier body profile.

Black Marble Swordtails are livebearers. Females give birth to fully formed free-swimming young rather than laying eggs and may produce repeated broods after mating.

Pregnant females become noticeably fuller towards the rear of the abdomen before giving birth. Fry immediately seek dense plants and sheltered areas where they graze on microscopic foods.

Individual Black Marble Swordtails can vary considerably in pattern, with some fish displaying extensive black coverage and others showing lighter marbling or irregular patches.

Aquarium Category:
Community Fish

Black Marble Swordtails are well suited to established freshwater community aquariums containing similarly active and peaceful species.

Suitable companions include mollies, platies, larger peaceful tetras, rainbowfish, danios, barbs, peaceful gouramis and appropriately sized bottom-dwelling catfish.

Special Requirements or Care Notes:
Provide a spacious aquarium containing both open swimming areas and dense planted sections. Hardy plants, floating vegetation and fine-leaved plants provide useful shelter for females and newly born fry.

Maintain moderately hard, mineral-rich water. Swordtails generally perform poorly in consistently soft, acidic conditions and may become more vulnerable to stress and disease.

A secure aquarium cover is recommended because Swordtails are active swimmers and may jump when startled or during courtship.

Avoid keeping excessive numbers of males in limited accommodation. Persistent chasing and displaying can lead to stress, damaged fins and reduced feeding opportunities for subordinate fish.

When breeding, maintain approximately one male for every two or three females to distribute courtship attention. Female Swordtails are capable of storing sperm and may produce several broods after a previous mating.

Adult fish may consume newly born fry. Provide dense moss, floating plants and other fine cover if natural survival is desired, or move fry to a dedicated rearing aquarium.

Feed fry newly hatched Artemia, microworms, powdered fry foods and finely crushed flakes several times daily in small portions.

Swordtails can hybridise with closely related Xiphophorus species, particularly Platies. Keep breeding strains separately if preserving the Black Marble colour line is important.

Good filtration and regular partial water changes are important because Swordtails are active feeders and can create a relatively high biological load when maintained in groups.

Suitable for:
Beginner freshwater fishkeepers

Availability:
Common in trade

All images are a visual representation of the fish you will receive, made to be as accurate as possible. Please note that Mother Nature is a wonderful thing, and variation in patterns and colours will occur — that is part of the unique beauty of these animals.