• Scientific name: Xiphophorus pygmaeus
• Synonyms: -
• Common name: Pygmy swordtail
• Group: Livebearers
• Habitat: Central America; Northeastern Mexico
• Size: 4 cm
• Biotope: Inhabits quiet areas of Pánuco River system.
• Social behavior: Peaceful and active schooling fish, that can be combined with other small fish. Males can be violent during the spawning season.
• Diet: Omnivorous; will accept most foods, but they also need some vegetable matter, such as algae.
• Breeding: Easy
• Tank: Minimum 40 litres
• Population: 1 male and 3-4 females for 40 litres
• Decoration: Needs a tank with dense vegetation where the females can find hiding places among the plants. Fine leaved plants like java moss will provide secure hiding places for fry.
• Temperature: 24-28 °C
• pH: 7.2-7.8
• Hardness: 5-18 NK°
• Lifespan: 3-6 years

Description: Xiphophorus pygmaeus is a small slender fish. Its body has three dark vertical lines, one along the lateral line, one along the spine and one from the base of the caudal fin to the anal fin. The fins are mostly translucent. Color of the male’s body is olive-gold, while the female is more browner.

Males have a distinctive gonopodium and the elongated "sword" on the caudal fin. Females have more plumper belly. Pygmy swordtail is a livebearer fish, the fertilisation happens inside the female’s body. The males can be very persistent during the courtship. The pregnat female can recognized by the dark pregnat-spot on her belly, which spot will enlarge with time. The gravid female should be separated as the adult fish will eat the fry. The gestation period of the female is usually 1 month, and after this time the female gives birth to 8-10 fry.