In 5 to 6-quart slow cooker, combine onions, celery, garlic, tomatoes, clam juice, tomato paste, wine, vinegar, oil, Italian seasoning, sugar, pepper flakes and bay leaf; mix well.
Cover; cook on High setting for 4 hours.
Stir fish, shrimp, clams with juice and crabmeat into stew. Reduce heat setting to Low; cover and cook an additional 30 to 45 minutes or until fish flakes easily with fork.
Just before serving, remove and discard bay leaf. Stir in parsley.