Try this The Original Fish Taco Recipe.
Achieving a crisp exterior on cod or hoki requires balancing flour and effervescent liquid. Whisk the flour with inexpensive carbonated beer until the mixture resembles a foamy paste. Carbon dioxide bubbles expand in hot oil, creating a porous, light crust that prevents the dense flesh from absorbing excessive fat. Coat the fish chunks evenly immediately before frying to maintain structural integrity.
Maintain oil temperature around 375 degrees Fahrenheit to ensure rapid dehydration of the batter surface. Submerge coated portions in small batches to prevent thermal drop in the pan. Watch for a deep golden hue as a visual indicator of doneness, which typically occurs within three to four minutes depending on piece thickness.
Construct the final dish rapidly to preserve textural contrast between hot protein and cool toppings. Spread a blended emulsion of mayonnaise and salsa down the center of a warmed tortilla to create a moisture barrier. Layer shredded cabbage over the sauce just before serving so the crisp leaves retain crunch against the steaming components.