Preheat oven to 375°F. and generously brush 2 large baking sheets with some oil.
With a mandoline or other hand-held slicer cut 1 potato crosswise into 1/8-inch-thick slices. Immediately arrange slices in one layer on 1 baking sheet and brush tops with some oil.
Sprinkle slices with salt to taste.
Bake slices in middle of oven until golden, 10 to 15 minutes, and with a metal spatula immediately transfer to a rack to cool completely. Make more chips with remaining potato. Potato chips may be made 3 days ahead and kept in an airtight container at room temperature.Top each potato chip with 1/4 teaspoon sour cream and a small piece of mackerel.
