Koi carp

Ornamental pond fish originating from Japan. They can live for decades, reach considerable sizes and develop extraordinary colours.

Detailed explanation

Koi carp (Cyprinus carpio koi) are the ornamental form of the common carp, selected in Japan for centuries for their colours and patterns. There are dozens of classified varieties (Kohaku, Sanke, Showa, Asagi, Shusui, Ogon, Bekko) and each variety has its own judging criteria in competitions.

A quality koi can cost thousands of euros. Japanese competition koi reach prices of tens of thousands of euros. Israeli and Asian (non-Japanese) koi are cheaper and suitable for most hobbyists.

The koi pond should be at least 120 cm deep (150 is better) with a minimum volume of 5000 litres for a small group. Koi grow according to the space available but in a pond that is too small they develop health problems.

Filtration is critical. Koi produce a huge bioload. The filter must process the entire pond volume at least once every 1-2 hours. Multi-chamber filters with generous volumes of biological material are the standard. Drum systems (drum filters) automate mechanical cleaning.

Koi diet varies with the seasons. In summer (above 18°C) they feed with high protein content feed (30-40%) to promote growth. In spring and autumn (10-18°C) we switch to easily digestible feed (wheat). Under 10°C koi go into semi-hibernation and do not eat.

The quality of the water must be monitored regularly: ammonia, nitrites, nitrates, pH, KH. Koi tolerate a wide pH range (6.5-8.5) but do not tolerate ammonia spikes.

The most feared parasite is the KHV virus (Koi Herpes Virus). Highly contagious and often lethal. Quarantine of new arrivals for at least 4-6 weeks is essential.

Koi can live 25-35 years. The longest documented one exceeded 200 years (according to Japanese tradition, not scientifically verified).

Reference values by aquarium type

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