Slow Cooker Cioppino

2 medium stalks celery, finely chopped (about 1 cup)

5 cloves garlic, finely chopped (about 2 1/2 teaspoons)

1 can (28 oz) diced tomatoes, undrained

1 bottle (8 oz) clam juice

1 can (6 oz) tomato paste

1/2 cup dry white wine or water

1 tablespoon red wine vinegar

1 tablespoon olive or vegetable oil

2 1/2 teaspoons Italian seasoning

1/4 teaspoon sugar

1/4 teaspoon crushed red pepper flakes

1 dried bay leaf

1 lb firm-textured white fish, cut into 1-inch pieces

3/4 lb uncooked medium shrimp, peeled, deveined

1 can (6 1/2 oz) chopped clams with juice, undrained

1 can (6 oz) crabmeat, drained

1/4 cup chopped fresh parsley