Kohaku Swordtail

The Kohaku Swordtail is an artificially bred selective form that does not occur in nature. The fish has an elongated, laterally compressed body, characteristic of the species Xiphophorus hellerii. Its coloration resembles Japanese koi carp: red or orange spots are located on a white background, most often on the head and caudal region. Sexual dimorphism is clearly expressed: males are slimmer and have a characteristic “sword” — elongated lower rays of the caudal fin — as well as a gonopodium. Females are larger, more massive, and do not have elongated fins.

In nature, the species inhabits bodies of water in Central America, including Mexico and Guatemala, populating both fast-flowing mountain rivers and stagnant waters of lakes, ponds, and swamps. The Kohaku variety is a result of selective breeding and is not found in natural conditions. In an aquarium, the fish adapt to a wide range of water parameters, provided the environment is stable and there is good aeration.

This is an active and peaceful fish, suitable for community tanks with similarly sized tankmates. Within the species, males may show territoriality and rivalry, so it is recommended to keep them in groups to disperse the attention of the dominant individual. The fish often occupy the middle and upper layers of the water. It is important to cover the aquarium, as swordtails are capable of jumping out of the water.

For long-term and successful keeping, as well as breeding, the Kohaku Swordtail will require a spacious aquarium of 100–150 liters or more. This volume will be sufficient for keeping about a dozen individuals, provided regular care and stable operation of all equipment, especially the filtration system. The aquarium decor can be anything, determined by the aquarist's preferences or the requirements of other inhabitants. Kohaku Swordtails prefer water with medium hardness and neutral pH values, while also being able to adapt to brackish water. These fish tolerate significant temperature fluctuations well and can feel comfortable in unheated aquariums if they are located in living quarters. As for feeding, Kohaku Swordtails are completely undemanding. Their daily diet can consist of common dry foods, such as flakes or granules. Live or frozen foods, such as Artemia, bloodworms, Daphnia, and other invertebrates, will be an excellent addition. The Kohaku Swordtail is an active and mobile fish that will swim throughout the entire aquarium space. Intraspecific conflicts are not observed. Males compete for the attention of females, but this rivalry is primarily demonstrative and rarely escalates into real skirmishes. These fish are compatible with many peaceful freshwater species of comparable size. It is advisable to avoid cohabiting different varieties of Swordtails and Platies to prevent the appearance of hybrid offspring. Crossbreeding is also possible with closely related Mollies.

Swordtails are omnivorous and undemanding in their diet. In the aquarium, they readily accept high-quality dry foods in the form of flakes or granules. To maintain vibrant coloration and health, it is recommended to supplement their diet with live or frozen foods, such as Artemia, bloodworms, or Daphnia, as well as plant-based additives like spirulina or blanched vegetables.

The species is live-bearing: fertilization is internal, and the female carries the fry for 4–6 weeks. Sexually mature males have a gonopodium. For breeding, it is recommended to move a pregnant female to a separate aquarium with dense vegetation, as parents may eat their offspring. One female can produce from 20 to 100 or more fry, which are immediately ready to feed independently.

With clean water, regular water changes, and a balanced diet, the fish have strong immunity. Common problems include infections caused by protozoa or bacteria, often arising from stress or unsatisfactory water quality. Prevention involves quarantining new individuals and maintaining stable environmental parameters.

When purchasing, choose active fish with clean scales, without visible fin damage, ulcers, or white film. Healthy swordtails show curiosity and are constantly in motion. Avoid individuals that stay near the surface, appear emaciated, or have unnaturally clamped fins, as these are signs of hidden diseases or stress.