Berlin Swordtail

The Berlin Swordtail is a selective breeding form obtained by crossing the Black-tailed Platy and the Green Swordtail. The fish has an elongated, laterally compressed body and the species-specific 'sword' — an elongated lower ray of the caudal fin in males. The main body coloration is a rich red-orange, and the fins often have a dark or black hue. Adult specimens reach 14–16 cm in length, with females typically being larger than males and lacking the sword-like appendage.

This selective breeding form is not found in the wild. The original species, Xiphophorus hellerii, inhabits freshwater bodies of Central America, including rivers and streams in Mexico, Guatemala, and Honduras. In their natural environment, these fish prefer areas with dense vegetation, calm or moderate currents, and a rocky-sandy bottom.

These are active and peaceful fish, suitable for a community tank. Males may exhibit intraspecific aggression and territoriality, so it is recommended to keep a group with a predominance of females, for example, a ratio of 1 male to 3 females. They are compatible with similarly sized peaceful species such as tetras, corydoras, and other livebearers, but cohabitation with slow-moving fish with long, flowing fins is not recommended.

Provided with a suitable environment, this fish does not require excessive attention. Optimal conditions for its keeping are achieved in a spacious aquarium, where warm and clean water of medium to high hardness is maintained. Swordtails also thrive in brackish water. For decor, shelters are desirable, such as dense plant thickets, which will allow less dominant individuals to hide. The territorial behavior of the dominant male often manifests as chasing weaker conspecifics. Towards other species, the fish are peaceful; they can be successfully kept with many non-aggressive species of comparable size. The diet includes dry foods such as flakes and granules, which can be alternated daily. Frozen or live foods, such as brine shrimp, bloodworms, or daphnia, will be an excellent supplement.

An omnivorous species. In the aquarium, they accept high-quality dry foods in the form of flakes or granules. The diet should be supplemented with live or frozen foods such as Artemia, Daphnia, bloodworms, or cyclops. To maintain vibrant coloration and health, it is recommended to include vegetable additives in their diet, such as spirulina or blanched vegetables.

Breeding these fish presents no difficulties. If the keeping conditions are favorable, mature male and female will regularly produce offspring. However, it should be noted that Berlin Swordtails readily crossbreed with both closely related species and other varieties. Therefore, to preserve the purity of the strain, it is crucial to avoid cohabiting them with other swordtails and platies.

With proper keeping conditions, quality filtration, and regular water changes, they possess a strong immune system. Common problems are often associated with improper feeding or poor water quality, which can lead to infections or swim bladder disorders. Prevention includes quarantining new individuals and maintaining stable environmental parameters.

When purchasing, choose active fish with clean fins, without visible damage, spots, or film on their scales. It is important to observe their behavior in the store: healthy individuals should show interest in food and swim actively. Avoid buying fish that appear emaciated, stay at the surface, or show signs of apathy.