Tosakin

The Tosakin is a rare selective breed of goldfish with a short, egg-shaped body and a pointed head. Its main feature is a unique, undivided caudal fin that, when viewed from above, forms a wide fan curling forward at the edges. The fins are well-developed, and a dorsal fin is present. Coloration varies from red and orange to white, calico, and black. Adult specimens reach 15–20 cm in length.

This species is an artificially bred selective form and does not occur in the wild. The breed was created in Japan in the 19th century (Kochi Prefecture). Due to the specific structure of their body and fins, these fish are not adapted to survival in natural bodies of water.

A peaceful, slow-moving, and social fish. Due to the specific structure of their tail, Tosakins swim clumsily and slowly, making them less competitive for food compared to more active species. Species-only tanks or cohabitation only with other slow-moving goldfish breeds are recommended. These fish are prone to stress and require a calm environment.

They require a spacious aquarium with a large surface area, preferably shallow. The absence of current is important, as these fish are weak swimmers. Effective filtration is necessary to maintain high water quality, as the species is sensitive to pollution. Regular water changes are recommended. The substrate should be smooth, without sharp edges, to avoid damaging fins and eyes.

An omnivorous species. Their diet should include high-quality dry foods in the form of pellets or flakes, supplemented with vegetable components (spinach, zucchini) and frozen foods (brine shrimp, daphnia, bloodworms). Moderation in feeding is important, as these fish are prone to overeating and digestive problems.

Breeding is considered difficult and is best suited for experienced aquarists. Spawning can be in pairs or groups. To stimulate spawning, increased temperature and imitation of seasonal changes are used. Fry require careful selection (culling) to fix breed characteristics, especially tail shape. At an early age, juveniles are often kept in special containers for proper fin development.

They are most susceptible to swim bladder diseases, which is often associated with their body shape and selective breeding. Fin damage, fungal infections, and parasitic diseases can also occur with poor water quality. They are sensitive to stress and sudden changes in environmental parameters, requiring stable keeping conditions.

When purchasing, choose active, outwardly healthy specimens without signs of fin damage, ulcers, or unnatural film on the body. It is important to assess the symmetry of the tail, as this is a key breed characteristic. It is recommended to purchase fish from specialized breeders, as high-quality specimens are extremely rare in general retail.