An unagi saki (鰻裂き) is the Japanese eel knife: unagi is freshwater eel and saki means to split, and opening eels for grilling is its one job. It is a single-bevel blade, ground on one side, with a straight edge and a straight spine. Each region has its own shape; the Tokyo form, the Edo saki, ends in an angled front that rises from the edge to a sharp point on the spine line. Typical lengths run from 180mm to 210mm.
The eel is pinned to the board through the head, then the point goes in and the blade runs the length of the fish, opening it flat along the backbone ready for kabayaki. Kanto (Tokyo) cooks open the eel along the back and Kansai cooks along the belly. Compared with a deba, it is lighter and narrower, made for this one long, controlled cut rather than for heads and bones.
