Xiphophorus hellerii

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Xiphophorus hellerii, also called Brick Swordtail, is a popular livebearer recognized by the sword-shaped extension that lengthens the male’s caudal fin. Native to Atlantic Central America, it inhabits warm, fresh waters that are generally well oxygenated. Its hardiness, constant activity, and easy breeding make it a common choice for beginning aquarists. Despite this reputation, it requires a spacious aquarium, stable water, and a good female-to-male ratio because males may repeatedly pursue females. The Brick variety displays an especially attractive reddish-orange coloration. With suitable tankmates and regular maintenance, it remains a lively and rewarding community fish.

General species description

Xiphophorus hellerii is a livebearing fish from the Poeciliidae family, related to platies and guppies. It is valued for its slender shape, active nature, and strong adaptability. The Brick Swordtail is a selectively bred form with a mainly red or orange-brick coloration; it is not a separate species. In aquariums, the species is best kept in groups with more females than males to reduce persistent courtship. A balanced group may produce fry regularly because fertilization is internal and females give birth to fully formed young. This is a **very common** aquarium fish. It suits community aquariums with peaceful species of similar size, while aggressive or fin-nipping tankmates should be avoided.

Geographic origin and biotope

Xiphophorus hellerii is native to the Atlantic drainage of Mexico, Guatemala, Belize, and Honduras. It occurs in rivers, streams, canals, and slower areas connected to lowland or foothill waterways. The water is generally soft to moderately hard, neutral to alkaline, and well oxygenated, with a relatively stable tropical temperature. Its habitat includes sunny sections, slow margins, and shelter formed by roots, branches, and aquatic plants. Streamside vegetation provides shade and supports small food organisms. In an aquarium, effective filtration, moderate current, and open swimming space reproduce its needs better than an overly crowded layout. Its presence in several drainage systems and introduction to other regions also explain its broad current distribution.

Specific locality and local name

In its natural range, Xiphophorus hellerii is associated with several coastal drainage systems along the Atlantic side of Mesoamerica, especially eastern and southeastern Mexico, as well as Guatemala, Belize, and Honduras. Populations may differ somewhat between drainages, particularly in coloration and fin shape. In Spanish, it is commonly called pez espada or pez cola de espada, names referring to the elongated caudal fin of the male. The English name Brick Swordtail describes the brick-red coloration of this commercial variety. In the aquarium trade, “swordtail” is also widely used. Captive-bred forms should not be treated as representing one precise locality because commercial selection has mixed different lineages.

Appearance and physical characteristics

Xiphophorus hellerii has an elongated, laterally compressed body covered with small scales. The Brick form is distinguished by a reddish-orange to brick-red coloration, sometimes lighter on the belly and deeper on the fins. The adult male has a lower extension of the caudal fin forming the characteristic sword; females lack this extension and usually have a fuller abdomen. The male’s anal fin is modified into a gonopodium used for internal fertilization. Size depends on lineage, diet, and rearing conditions, but females are often larger and heavier-bodied. Juveniles may be difficult to sex until the gonopodium and sword become clearly developed.

General diet

Xiphophorus hellerii is omnivorous, with an important plant component in its natural diet. It grazes algae and biofilm from surfaces while also eating small invertebrates, larvae, and other particles found among vegetation. In an aquarium, a quality flake or pellet food can be supplemented with vegetable-rich foods such as spirulina, along with small frozen or live foods. Variety supports coloration, growth, and reproduction. Small portions once or twice a day are preferable, and uneaten food should not be allowed to decay. Fry benefit from very fine foods, such as powdered fry food or newly hatched brine shrimp. Regular access to **fiber and plant matter** helps support healthy digestion.

Essential data

• Name of the original river: Coastal Atlantic river systems within the native range.
• Local name used: Pez espada; pez cola de espada.
• Origin of the scientific name: A name built from Greek roots and a person’s name.
• Etymology of the full name: Xiphophorus means “sword bearer”; hellerii honors Carl Heller.
• Common/vernacular names: Swordtail, Brick Swordtail, porte-épée.
• Family: Poeciliidae.
• Subfamily: Poeciliinae.
• Name pronunciation: zik-foh-for-us hel-ler-ee-eye
• Discovery: Carl Heller, 1848.
• Maximum adult size: About 14 cm for males including the sword; females may reach about 16 cm.
• Water temperature and pH: 22 to 28 °C; pH 7.0 to 8.3.
• Stream appearance and surrounding vegetation: Tropical waterways, quiet margins, dense vegetation, roots, and shaded areas.
• Typical tankmates: Poecilia reticulata, Xiphophorus maculatus, Corydoras paleatus.
• Temperament and behavior: Active and generally peaceful; males pursue females and may compete with one another.
• Water depth: Shallow to moderately deep areas, especially near the margins.
• Sexual dimorphism: Males are smaller and have a gonopodium and sword; females are larger, lack the sword, and have a rounder abdomen.
• Bottom structure and flow: Sandy, gravelly, or muddy substrate; slow to moderate flow with quieter areas.

In your aquarium

For successful care of Xiphophorus hellerii, choose a long aquarium of at least 100 litres for a small group, with open swimming space and plants for shelter. Keep the water clean, stable, and sufficiently mineralized, avoiding sudden changes in temperature or pH. A ratio of about one male to two or three females helps reduce stress caused by courtship. Feed a varied diet and expect fry if males and females are kept together. Filtration should provide steady circulation without turning the aquarium into a torrent. With these conditions, this **very hardy and colorful fish** remains an excellent community choice.