Kois

Kois are ornamental varieties of the common carp (Cyprinus rubrofuscus) kept in outdoor ponds for decorative purposes. They belong to the family Cyprinidae and were extensively bred in Japan from the 19th century, with breeding programs later spreading worldwide. Kois are selected for color, pattern, and body form rather than meat quality.

Koi come in many varieties distinguished by color patterns and scale types. Classic patterns include Kohaku (white body with red), Taisho Sanke (white with red and black), and Showa Sanshoku (black body with red and white). Other common types include Asagi (blue-gray with red along the dorsal line), Shusui (scaleless, blue-gray with red or white), Utsuri (black with white or colored markings), Bekko (white or yellow with black spots), Kujaku (pearl-like metallic with orange and white), Ogon (solid metallic colors), and Tancho (white with a single red spot on the head). Doitsu forms are scaleless. Color genetics are polygenic and breeding continues to expand varieties.

Keeping kois requires a large, well-filtered pond with reliable aeration. They prefer stable temperatures, typically 15–29°C (60–85°F), and a pH near neutral to slightly alkaline. Provide shaded areas and cover sharp objects. A mature pond with adequate filtration can support several koi; feeding consists of high-quality pellet foods supplemented with vegetables. Avoid overfeeding to protect water quality.

Reproduction occurs in spring as water warms; females lay thousands of eggs that cling to submerged surfaces. Lifespan commonly ranges from 25 to 35 years, with longer lifespans possible in favorable conditions. Disease risks include koi herpesvirus (KHV), ich, parasites, and bacterial infections; good water quality, quarantine of new fish, and routine health monitoring are important.

Culturally, koi symbolize perseverance, strength, and luck in Japan and many garden traditions, where koi ponds are central features of landscape design.