Obviously this works with any fish that's good fried, which is most of them. Avoid oily fish like mackerel or bluefish or herring, and I really don't this this is an ideal recipe for salmon or trout. But other than that, go for it. The accompaniments to the tacos are also up to you. What's in this recipe are what I like with fish tacos, but regular salsa works, as would chopped tomato, and lots of people like to mix chipotles in adobo with mayonnaise and drizzle that on top.
Cut the fish into pieces that will fit inside a tortilla. Salt the fish and set aside. Heat the oil in a heavy pot or fryer until it's 350°F. While the oil is heating, mix all the dry ingredients for the batter -- the flour, corn starch, baking soda and salt -- in a large bowl. Have the egg yolk and icy sparkling water handy.
Heat the oven to"warm." Set a wire rack on a baking sheet and put that in the oven.
When the oil is hot, mix the egg yolk and sparkling water into the batter. Do not beat the heck out of it, you want it lumpy and barely incorporated. Dredge a piece of fish in the batter and slowly dip into the hot oil. Doing this slowly allows the bottom of the fish to set a bit, which reduces the chance the fish will stick to the bottom of the pot. Repeat with as many fish pieces as you can get into the hot oil without crowding.
Fry until golden, using a chopstick or fork to flip the pieces over. This should take between 4 and 8 minutes depending on the thickness of your pieces. When they're done, move the fish to the rack in the oven and repeat with the remaining fish.
When all the fish is ready, move it to a platter and arrange all the accompaniments to the table. Let everyone make up their own tacos.