This huge fish, whose name means "beach stroker", first appeared in Shunsen Takehara's 1841 illustrated collection of strange stories, the Tōsanjn Yawa
. It is described therein as follows:
On the open sea of Matsura, in Hizen*, when the north wind blows violently, without fail the fish called isonade appears raging in the ocean. If a boat happens by at this time, this fish uses its tail to drag the people in the boat into the sea, where it devours them. In shape it is a great fish resembling a shark**. On its tail hooks like iron grow backwards. The event of a travelling priest being taken by a crocodile on the seashore of Hotte, in Buzen†,
appears in the Tanchō Banashi, but the thing called a crocodile seems to be this isonade. The thing which appears in the Honzō Ikō as the kyokōgaku (giant-mouthed crocodile) also is said to be this isonade. Therefore, one must take care while voyaging on the sea.1
An account of the isonade was also recorded in a collection of folklore from Mie Prefecture, published in 1960 by the Kokugakuin University Folklore Research Society. Here the isonade is described as a shark with a long tail, which it strikes on the edge of the seashore. When people are found dead on the beach, it is said they were "stroked" by the isonade.2
*Now Saga and Nagasaki Prefectures.
**While this character currently means "sturgeon", its reading is given as "fuka" or "shark".
†Now Fukuoka Prefecture.
1. Takehara, pp. 11, 62, 130.
2. KYDD Summary: Isonade. from "Mie-ken Kumano-shi Arasaka-chiku Hoka." Minzoku Saihō. Kokugakuin University Folklore Research Society, 1960. p. 52.