How to Identify Swordtail

To identify Swordtail (Xiphophorus hellerii), look at these key features.

Physical Characteristics

Body shape

elongated

Coloration

Wild-type Swordtails are typically olive-green to brownish-yellow, with a prominent reddish-orange stripe running laterally along the body, often bordered by a darker line. The 'sword' of the male is usually yellow, orange, or red, often edged in black. Through selective breeding, numerous color morphs exist in the aquarium trade, including red, black, albino, pineapple, and various patterned varieties.

Scale type

cycloid

Mouth position

superior

Distinctive features

Males possess a distinctive, elongated lower caudal fin ray resembling a 'sword'., Sexual dimorphism: males are smaller with a sword and gonopodium; females are larger and lack the sword., Lateral stripe often present.

Dorsal fin

Single dorsal fin, typically with 10-14 rays.

Tail fin

Caudal fin is rounded in females. In males, the lower rays are greatly extended to form the 'sword'.

Pectoral fin

Paired pectoral fins, typically clear or slightly colored.

Distinctive fins

Anal fin of males is modified into a gonopodium for internal fertilization. Pelvic fins are small and paired.

Identification Tips

1. 1

   Male 'Sword'

   The most definitive feature for males is the elongated, sword-like extension of the lower caudal fin. This is absent in females.

2. 2

   Body Shape and Size

   Males typically reach 8-10 cm (3-4 inches) excluding the sword, while females can grow larger, up to 12-14 cm (5-5.5 inches). The body is elongated and somewhat compressed laterally.

3. 3

   Gonopodium

   Males possess a modified, rod-like anal fin (gonopodium) used for internal fertilization, which is distinct from the fan-shaped anal fin of females.

4. 4

   Coloration

   While wild types are greenish with a lateral stripe, aquarium strains exhibit a wide array of colors. The presence of the sword and body shape are more reliable identifiers than color alone.

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