Koi (Cyprinus carpio) are very well know and popular domesticated varieties of the common carp and their average life span is approximately 50 years. However, there are many known to age more than 100 years and this is probably why these fish have gained so much admiration in Japan and the rest of the world.
‘Hanako’ died at the grand old age of 226 on July 7, 1977! Born in 1751, incredibly 25 years before American independence, she weighed 7.5 kg and was 70 cm long. Her age could be reliably documented by analysing the rings on her scales, much in the same way that the age of trees are determined by counting the number of growth rings in the wood. These ‘annual rings’ on a fish’s scale are too small to be seen by the human eye and so must be recorded with the use of a microscope. The process is so labour intensive that the analysis took about two months to get reliable result. Similarly, just like tree rings, the microscopic rings seen on fish scales reflect seasonal growth patterns, so where fish eat more and grow more in summer these rings are wider and winter scale rings are narrower.
‘Hanako’ spent her life in a pond at the base of Mt. Ontakein in Gifu, Japan with 5 other Koi who all lived to be well over 100 years old too. ‘Hanako’s’ last owner, Dr. Komei Koshihara, inherited the carp as it had been handed down through many of the family’s generations. ‘Hanako’s’ final owner claimed that she was very hand-tame and would always come to the pond’s edge to be petted and fed when she called her!
Nobody knows exactly the reasons for her amazing age but perhaps it was helped by the perfect life environment in the Japanese mountains, perhaps the crystal clear, fresh and healthy water in the pond, perhaps the individual genetics or the devoted care and love from the family? All of these could have made the slight difference but the wide range of reported life expectancies for Koi probably has to do with the variation of individual genetics, and in a large part, to differences in water quality and nutrition.