Heat olive oil in heavy large pot over medium heat. Add onion, garlic, oregano and fennel seeds and sauté until onion is tender, about 8 minutes. Add tomatoes, clam juice, white wine and liquid reserved from clams. Increase heat and boil until slightly thickened, about 15 minutes. Add clams, shrimp and crabmeat. Reduce heat and simmer 2 minutes. Mix in fresh basil and simmer until shrimp are just opaque in center, about 2 minutes longer. Season stew to taste with cayenne, salt and pepper.