Clean mussels as needed and discard any that aren't closed or don't close when handled. Set aside.
Sautee onion and garlic in olive oil until just soft, about 5 minutes.
Add dried crushed red pepper, oregano, tomatoes, olives, capers, anchovies and parsley. Simmer until flavors combine and sauce thickens some, about 10 minutes.
Add whitefish to sauce, cover and cook until almost done, about 5 minutes.
Add mussels and cook until they open, about 5 minutes. Discard any mussels that don't open. Serve over hot cooked pasta.
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Notes
You can substitute 2-3 pints of cherry or grape tomatoes for the canned tomatoes.
I am not a health professional and nutrition data is calculated programatically. Accuracy may vary with product selection, calculator accuracy, etc. Consult a professional for the best information.