Stir together first 6 ingredients in a medium saucepan. Bring mixture to a boil, stirring occasionally, over medium-high heat. Boil 15 minutes, stirring occasionally, or until mixture is reduced by half. Stir in ketchup, brown sugar, and hot sauce; reduce heat, and simmer 10 minutes. Remove from heat; stir in lime juice and cilantro.
Note: Any thick, firm-fleshed white fish or boneless, skinless chicken breast can be used as a substitute for scrod. The sauce can be prepared up to 4 days to 1 day in advance and refrigerated, tightly covered.