In a large saucepan, heat first measure of olive oil over medium heat until shimmering. Add onion and garlic and cook, stirring regularly, until onion is soft and translucent.
Add fennel, celery, leek and carrot to pan and cook for 3 minutes. Add tomato paste and cook, stirring continuously, for 4 minutes.
Stir in stock, wine and vermouth then simmer for 30 minutes.
Transfer soup base to a blender then add salmon and whiz until smooth. Return sauce to pan and bring back to a simmer.
Stir in fennel, cream and Pernod and simmer for 2 minutes. Season to taste with salt and pepper then remove pan from heat and set aside.
Place flour in a plastic bag then add whitebait and toss well to evenly coat. Remove whitebait from bag and shake off excess flour.
In another frying pan, heat canola oil over medium-high heat. Add floured whitebait and stir-fry for 1–2 minutes, until golden and crispy. Remove whitebait from pan and place in a sieve to drain.
Return soup base to heat and bring back to a simmer. Add scallops then remove pan from heat, cover and set aside—the scallops will cook from the heat of the soup while you do the last steps.
In a frying pan, heat final measure of olive oil over medium heat. Add prawns and stir-fry until just cooked through.
To assemble, ladle soup into bowls then top each bowl with 2 prawns and the whitebait. Sprinkle with parsley (if using) and serve.