Koi mud ponds

The 'mud ponds' of Japan are famous and synonymous with koi breeding. They are used for growing on the young fry and Tategoi. They are hand made and are sited on hillsides that used to be occupied by paddy fields. These days however, there is more money to be made from cultivating Nishikigoi than there is from rice production. Excavators are used to dig out new ponds and the clay is tamped down by machine to make them watertight. The clay is also smoothed off for the benefit of the koi and to make it easier for netting them later in the season. The ponds vary in size from about 60sq metres ( 646sq feet) to vast ones of many hectares. The depth will depend on what they are used for, up to 1m (39 inches) for fry, to over 3m (10ft) for the larger fish. Stocking levels range from 8,000 to 15,000 fry per 100 kilolitres (22,000 gallons) of water. This level of stock is to allow for the four culls that are carried out throught the growing season. Summers in Japan are extremely warm, above 30 degrees C (86 degrees F) and this means that the ponds need heavy aeration. Large compressors are used or paddle type machines that agitate the waters surface. The best aeration possible is achieved as both methods force air - or dissolved oxygen - into the water. The only predator of koi, apart from man, is the heron. This bird is as much a nuisance to breeders in Japan as it is in the rest of the world. From the moment the ponds are stocked they are protected by nylon line and moving scarecrows, to deter the heron.