Xiphophorus hellerii

A Little More Information...

Xiphophorus hellerii, also called Neon Green Swordtail, is a selectively bred form of the popular swordtail Xiphophorus hellerii. It is recognized by the male’s long lower extension of the caudal fin and combines an active swimming style with a striking neon-green coloration. This form is very common in the aquarium trade and is suitable for properly planned community aquariums. Like other livebearers, it produces fully formed fry and can reproduce quickly. Clean, slightly alkaline water, good plant cover, and an open swimming area support its well-being and make its social behavior easy to observe.

General species description

Xiphophorus hellerii is a Central American livebearer and a domestic form of Xiphophorus hellerii. The species is known for its constant activity, midwater and upper-level swimming, and the male’s distinctive caudal sword, which inspired its common name. Neon Green Swordtail is selected for fluorescent green reflections, while its general body shape and behavior remain those of the standard swordtail. It is a very common fish that is hardy when maintenance is consistent, but it benefits from stable, well-oxygenated water. Females are usually deeper-bodied and give birth to live fry after gestation. Keeping several females for each male helps reduce repeated chasing and breeding pressure.

Geographic origin and biotope (reference countries: Mexico, Guatemala, Belize, and Honduras)

The natural range of Xiphophorus hellerii includes Atlantic-slope waterways in Central America, particularly in Mexico, Guatemala, Belize, and Honduras. The Río Nautla in Veracruz is associated with its Mexican range. It inhabits streams, rivers, and connected quiet-water areas, usually in fresh to slightly alkaline water. The biotope includes plant-covered banks, roots, branches, and illuminated areas where the current remains moderate. Water is often shallow along the margins, with stronger circulation toward the channel. In an aquarium, dense planting along the sides and back, combined with an open central area, recreates these general conditions effectively.

Precise location and local name

Within its native range, Xiphophorus hellerii is associated with Atlantic-slope waterways of Mexico, especially in the eastern and southeastern parts of the country, as well as neighboring Central American basins. The most common Spanish vernacular name is pez espada, meaning “swordfish,” while “cola de espada” directly describes the male’s caudal fin. In the aquarium trade, Neon Green Swordtail refers to the selectively bred variety with a bright green coloration. The French term porte-épée is used for the species and its many cultivated forms. Because this strain is produced through selection, its color is not an indicator of natural origin. Different varieties are best kept separately when maintaining a visually consistent strain is important.

Appearance and physical characteristics

Xiphophorus hellerii has an elongated, laterally compressed body with well-developed fins. The Neon Green variety displays a metallic to fluorescent green base color, sometimes enhanced by yellow or blue tones depending on lighting and strain. In adult males, the lower rays of the caudal fin form a long sword; its length and intensity vary among fish. Females lack the sword and are generally more rounded through the abdomen. The male also has a gonopodium, a reproductive organ modified from the anal fin. Size depends on the strain and rearing conditions, but large males may reach about 14 cm including the sword, while females are often heavier-bodied.

General diet

Omnivorous with a strong preference for plant matter, Xiphophorus hellerii readily accepts a varied diet. The staple can consist of quality flakes or micro-pellets, supplemented regularly with vegetable foods containing algae or spirulina. Frozen foods such as brine shrimp, daphnia, or mysis can occasionally be offered for variety. Fry benefit from fine foods given in small portions. A supply of fiber and plant matter helps prevent an overly protein-rich diet, while modest meals reduce waste. Adults are best fed once or twice daily, offering only what they consume quickly. Dietary variety, rather than overfeeding, supports good body condition and stronger coloration.

Essential data

• Native river name: Río Nautla and neighboring Atlantic-slope waterways of Mexico
• Local name used: Pez espada; cola de espada
• Origin of the scientific name: Xiphophorus hellerii was named by Johannes Jacob Heckel
• Full-name etymology: Xiphophorus means “sword-bearer”; hellerii honors Carl Heller
• Common/vernacular names: Swordtail; Neon Green Swordtail; Porte-épée
• Family: Poeciliidae
• Subfamily: Poeciliinae
• Name pronunciation: zik-soff-or-us hell-er-ee-eye
• Discovery: Johann Jakob Heckel, 1848
• Maximum adult size: About 14 cm for a large male including the sword
• Water temperature and pH: 22 to 28 °C; pH 7.0 to 8.3
• Waterway appearance and surrounding vegetation: Clear streams and rivers with moderate flow, planted banks, roots, and branches
• Typical tankmates: Poecilia reticulata, Xiphophorus maculatus, Poecilia sphenops
• Temperament and behavior: Active and generally peaceful, with male chasing and reproductive competition
• Water depth: Shallow marginal zones and quiet areas
• Sexual dimorphism: Male slimmer with gonopodium and caudal sword; female larger and rounder
• Bottom structure and flow: Sand, gravel, plant debris, and roots; slow to moderate flow

In your aquarium

Keeping Xiphophorus hellerii is generally straightforward when it is provided with a sufficiently long, well-filtered, covered aquarium, since this fish is an active swimmer and may jump. Maintain stable, slightly alkaline water, good oxygenation, and regular water changes. Keep several females per male to distribute breeding attention. Plants, roots, and open areas provide both shelter and swimming space. Monitor reproduction, as fry can quickly increase the population. A varied diet, consistent temperature, and peaceful tankmates are the main keys to long-term success.