Sweet smelt or freshwater trout. A lithe little fish which feeds on the algae at the bottom of rivers. This means that it will not take bait for the fishermen and so they train cormorants to catch them. The fishermen take them out in the darkness on moonless nights on their long shallow boats and shine lights to attract the fish. The birds' throats are bound so that they do not swallow the fish, which they bring back to the boats where they regurgitate them. This mode of fishing is called "ukai". They are served with a sauce of vinegar and nettles called tadesu. We attended a kaiseki ryori in Kyoto one May, the right season for these fish. One of the courses consisted of ayu. They were lightly fried and served whole, unlike many of the things which appeared in front of us that night which were predominantly raw, including sea cucumber. The late season ayu is known as ochiayu and is considered the best.