Heat oil in large deep skillet over high heat. Add bell pepper, sliced fennel, Italian sausage, and fennel seeds, and sauté until sausage is brown and vegetables are just tender, about 10 minutes. Add clam juice, and bring to boil. Add clams and oregano; reduce heat to medium-high, cover, and cook just until clams open, about 5 minutes. Season to taste with pepper. Divide among 4 bowls, discarding any unopened clams. Sprinkle with chopped fennel fronds and serve.