Set the instant pot to the saute function. Add the olive oil, fennel and onion to the pot and stir. Cook stirring often for about 5 minutes or until fragrant and beginning to soften. Season with the salt and stir in the tomato paste for 1 minute. Deglaze with the wine. Add the tomatoes, clam juice, bay leaf and pepper flakes. Secure the lid on the instant pot and cook for 20 minutes under high pressure.

Allow the instant pot to naturally release pressure for 10 minutes. Manually release any remaining pressure. Stir in the halibut, shrimp and clams and replace the lid. Cook under high pressure for 3 minutes. Quick release the pressure. Remove and discard the bay leaf and any unopened clams. Serve with a sprinkle of basil, drizzle of olive oil and crusty bread to soak up the broth if desired.