Peel and devein shrimp; set aside.
Scrub clams thoroughly, discarding any that are cracked or open. Place clams in a large bowl; cover with cold water, and sprinkle with cornmeal. Let stand 30 minutes. Drain and rinse clams; set aside. Discard cornmeal.
Coat a Dutch oven with cooking spray; add oil. Place over medium-high heat until hot; add onion and next 6 ingredients. Saute 5 minutes or until onion is tender. Add wine and next 4 ingredients. Bring to a boil; cover, reduce heat, and simmer 10 minutes. Add fish; cook, covered, 5 minutes. Add shrimp and clams; cook, covered, 3 additional minutes or until shrimp turn pink. (Discard any clams that do not open.)