Heat the oil in a large saucepan over medium heat. Add the onion, carrot, and chopped fennel and cook until softened, 6 to 8 minutes. Stir in the tomato paste.
Add the shrimp, clam juice, tomatoes and their juices, and 1½ cups water to the saucepan. Season with ½ teaspoon salt and ¼ teaspoon pepper. Simmer until the shrimp are opaque, about 2 minutes. Sprinkle with the fennel fronds.