3 tablespoons plus 1/4 cup olive oil
1 large onion, chopped
1 carrot, thinly sliced
1 celery stalk, thinly sliced
4 large garlic cloves, chopped
1 14 1/2-ounce can diced tomatoes in juice
3 8-ounce bottles clam juice
1 1/2 pounds mussels, scrubbed
12 littleneck clams, scrubbed
1 cup dry white wine
3 1/2 cups plain couscous (20 ounces)
1 1/2 teaspoons chopped fresh thyme
3 small bay leaves
2 pounds assorted fish fillets (such as halibut, cod and red snapper), cut into 1 1/2-inch pieces
8 ounces uncooked shrimp, peeled, deveined
Chopped fresh parsley
1/3 cup hot chili paste
1. Heat 3 tablespoons oil in heavy large pot over medium heat. Add onion; saute 5 minutes. Add carrot, celery, and garlic; saute 5 minutes. Add tomatoes with juices and 1 bottle clam juice and bring to boil. Reduce heat; simmer uncovered 10 minutes. Cover and simmer 10 minutes. Transfer mixture to processor. Blend to chunky puree; return to pot. Mix in 2 bottles clam juice to make tomato broth.
2. Combine mussels, clams, and wine in another large pot. Cover and cook over high heat until mussels and clams open, about 8 minutes. Using tongs, transfer mussels and clams to bowl (discard any that do not open). Strain cooking liquid into tomato broth.
3. Place couscous in large bowl. Bring 2 1/2 cups water, 3 cups tomato broth, and 1/4 cup oil to boil in medium saucepan. Mix into couscous. Cover; let stand until liquid is absorbed, about 10 minutes. Season with salt and pepper. Cover; let stand until ready to serve.
4. Meanwhile, mix thyme and bay leaves into remaining tomato broth in pot and bring to boil over medium-high heat. Add fish. Cover and simmer 4 minutes. Add shrimp; cover and simmer until seafood is opaque in center, about 4 minutes. Turn off heat. Add reserved mussels and clams. Cover; let stand 2 minutes.
5. Mound couscous on platter. Top with seafood. Spoon some tomato broth over to moisten. Sprinkle with parsley. Mix 3/4 cup tomato broth and hot chili paste in small dish. Serve couscous, passing chili mixture and remaining broth separately.