Shad is a very bony fish, which is why you need to use the honegiri bone-cutting technique on it before you fry the fish. You can also use this technique on any bony fish, such as pickerel or pike. You will need a very sharp knife and some practice to get this right. Just take your time at first.
Get your cooking oil up to 360-370 degrees. While the oil is heating, cut the shad fillets into serving pieces and salt lightly. Mix all the dry ingredients for the tempura batter. Turn your oven to the "warm" setting, and place a cookie sheet inside. Place a wire rack on top of the cookie sheet.
When the oil it hot, mix the egg yolk and the sparkling water into the dry tempura batter ingredients and stir only until just combined; it's OK to have a few lumps. Dip some of the shad into the batter, making sure the batter gets into the slits you cut into the fish using the honegiri technique. Fry the fish until golden brown, about 3-4 minutes. Make sure the fish does not stick to the bottom of the pot, and use a chopstick to dislodge any pieces that do stick.
When each batch is done, transfer it to the wire rack in the oven. When all the fish is done, serve at once with ponzu sauce, soy sauce or any other dipping sauce.