Eels have been eaten in Japan since antiquity, and they have always been regarded as a particularly nutritious food. It is recorded that a celebrated thief called Nihonzaemon, who was executed in 1747, was able to see in the dark and that he attributed this to a large consumption of eels. Since they are rich in vitamin A, the claim may have been true.
Most of the eels consumed in Japan are farmed. When farming began, towards the end of the 19th century, the eels were raised in artificial ponds, but now they are kept in indoor tanks under controlled temperature, and are given factory-made compound food.