Katsuo Sashiko is a type of Enshu (Shizuoka) weaving in which Sashiko is applied to a weave called Katsuo Stripes.
The stripes on the fabric are blurred from dark indigo to light indigo, just as the color of a skipjack's body gradually fades from back to belly, hence the name "katsuo kasuri" (skipjack pattern).
In the Edo period (1603-1868), the pattern was widely used for yukata and other clothing.
This American work shirt is made of a thick fabric with a dobby weave of skipjack stitch. The buttons are nut buttons.