Pat the fish pieces dry with paper towels. In a bowl, sprinkle 0.5 tsp salt, 0.25 tsp black pepper, 0.5 tsp garlic powder, and 0.5 tsp paprika over the pieces and toss gently to coat evenly. Let sit 5–10 minutes while preparing batter.

Make batter

In a medium bowl whisk together 1 cup all-purpose flour, 0.25 cup cornstarch, and 1 tsp baking powder. Stir in 1 tsp salt and 0.5 tsp black pepper. In a separate small bowl lightly beat 1 large egg. Pour the egg and 1 cup cold sparkling water into the dry mix and whisk just until combined; the batter should be slightly thick but still pourable with some bubbles. Keep the batter cold (set bowl over ice if your kitchen is warm).

Dredge fish

Place extra 1/4 cup flour in a shallow dish for dredging. Working in batches, lightly dredge each seasoned fish piece in the flour, shaking off excess, then dip into the batter to coat completely. Let excess batter drip off before frying.

Frying

Heat oil

Pour 4 cups oil into a heavy-bottomed pot or deep skillet to a depth of about 2 inches. Heat over medium-high until oil reaches 350–360°F (175–182°C). If you don't have a thermometer, test by dropping a small drop of batter: it should sizzle and rise immediately without burning.

Fry fish bites

Fry the battered fish in small batches (do not overcrowd) for 2.5–4 minutes per batch, turning once if needed, until batter is golden brown and fish reaches an internal temperature of 145°F (63°C) or flakes easily. Use a slotted spoon or spider to remove fish and drain on a wire rack set over a baking sheet or on paper towels. Keep cooked batches warm in a 200°F (95°C) oven if preparing multiple batches.

Finish & season

Immediately after frying, sprinkle fish bites lightly with a pinch of salt (adjust to taste) and chopped parsley if using. Serve hot with lemon wedges.

Dipping Sauce (Tartar-style)

While the oil heats and fish rests, combine 0.5 cup mayonnaise, 2 tbsp dill pickle relish, 1 tbsp chopped capers (optional), 1 tbsp fresh lemon juice, 1 tsp Dijon mustard, 0.25 tsp freshly ground black pepper, and 1/8 tsp salt in a small bowl. Mix until smooth and taste; adjust lemon, salt, or mustard to preference. Chill until ready to serve.