Heat the olive oil in your large pot over medium heat. Add the onions and fennel. Cook them for about 10 minutes until they are soft. This builds the base flavor for your stew.

Stir in the garlic, oregano, and red pepper flakes. Cook for just one minute. You will smell the amazing aroma. Be careful not to burn the garlic as it turns bitter.

Add the tomato paste to the pot. Stir it well with the vegetables. Let it cook for two minutes. This makes the broth rich and deep in color and flavor.

Pour in the white wine. Use your spoon to scrape any brown bits from the bottom. These bits have lots of flavor. Let the wine simmer for a few minutes to reduce.

Add the crushed tomatoes and seafood stock. Bring the liquid to a boil. Then turn the heat down. Let it simmer uncovered for 30 minutes to thicken and blend the spices.

Gently stir in the chunks of white fish. Cover the pot and cook for 3 to 5 minutes. The fish should just start to turn opaque and firm to the touch.

Add the shrimp, mussels, and clams to the pot. Cover it again. Cook for 5 to 10 minutes. The shrimp will turn pink and the shells will open wide.

Check the stew. Throw away any shells that did not open. Stir in the fresh parsley. Add salt and pepper if needed. Serve it hot and fresh immediately.