Preparation Steam squash until almost tender, about 10 minutes. Cool. (Can be prepared 1 day ahead. Cover and chill.) Heat olive oil in heavy large pot over medium heat. Add chopped onion, chopped fennel and minced garlic and sautéuntil translucent, about 3 minutes. Add tomato paste, chopped fresh thyme and bay leaf and stir 1 minute. Add clam juice, tomatoes with juices, white wine, Sherry and 1/2 cup water and bring to boil. Reduce heat to medium, cover and simmer 20 minutes to blend flavors. Discard bay leaf. Add clams and saffron to pot; cover and cook until clams open, about 4 minutes (discard any clams that do not open). Add sea bass and steamed squash to stew. Cover and simmer until squash is tender and fish is just opaque in center, about 5 minutes. Season stew to taste with salt and pepper. Ladle stew into bowls. Garnish with fennel fronds, if desired, and serve.
Preparation Steam squash until almost tender, about 10 minutes. Cool. (Can be prepared 1 day ahead. Cover and chill.) Heat olive oil in heavy large pot over medium heat. Add chopped onion, chopped fennel and minced garlic and sautéuntil translucent, about 3 minutes. Add tomato paste, chopped fresh thyme and bay leaf and stir 1 minute. Add clam juice, tomatoes with juices, white wine, Sherry and 1/2 cup water and bring to boil. Reduce heat to medium, cover and simmer 20 minutes to blend flavors. Discard bay leaf. Add clams and saffron to pot; cover and cook until clams open, about 4 minutes (discard any clams that do not open). Add sea bass and steamed squash to stew. Cover and simmer until squash is tender and fish is just opaque in center, about 5 minutes. Season stew to taste with salt and pepper. Ladle stew into bowls. Garnish with fennel fronds, if desired, and serve.