Slow Cook Seafood Stew

3 pounds uncooked clams in shells
6 cups water
1/3 cup white vinegar
1 large onion, chopped (1 cup)
1 cup Progresso® chicken broth (from 32-ounce carton)
1/2 cup dry white wine or Progresso® chicken broth

1 tablespoon tomato paste
2 tablespoons chopped fresh oregano leaves or 1/2 teaspoon dried oregano leaves
1 teaspoon fennel seed
1/8 teaspoon saffron threads, if desired
1/8 teaspoon ground red pepper (cayenne)
2 large tomatoes, chopped (2 cups)
1 pound red snapper or whitefish fillets, cut into 2-inch pieces
3 cups cooked white rice
2 tablespoons chopped fresh parsley
2 teaspoons grated lemon peel