Melt butter in large saucepan over low heat; remove from heat and stir in flour until smooth. Return to heat and cook, stirring, for 10 minutes, until roux is dark brown. Stir in chopped white and green onions, celery and garlic; cook about 10 minutes. Add tomato paste to fish stock; stir into onion mixture. Add tomatoes, crayfish, parsley and seasonings; cover and simmer 20 minutes. Serve over hot rice.