Kawakawa (Euthynnus affinis) スマ
Kawakawa have many names Wavyback Tuna, Mackerel Tuna, or Little Tuna are some of them. I call them Kawakawa which is the Hawaiian name. I would catch them while sailing occasionally in Hawaii. For tuna they are very small. This school went by me at the edge of the reef. Amami
More pictures of the same school of Kawakawa. Amami