White Seafood Brodetto

Name: White Seafood Brodetto
Ingredients: 1 1/2 pounds swordfish, dark spots trimmed, cut into 1 1/2-inch cubes; Kosher salt; All-purpose flour, for dredging; 5 tablespoons extra-virgin olive oil; 4 cloves garlic, thinly sliced; 1 large onion, sliced; 1 teaspoon red pepper flakes; 3/4 cup dry white wine; 1 pound manila clams (about 24), scrubbed; 1 pound large shrimp, peeled and deveined; 1 pound small calamari, tentacles separated, bodies sliced into rings; 3 tablespoons unsalted butter; 1/2 cup chopped fresh parsley; 3 tablespoons white wine vinegar or fresh lemon juice; Grilled or toasted crusty bread, for serving