Place a large saucepan of salted water over high heat and bring to the boil. Place crab in saucepan and cook for 15-18 minutes. Cool in an ice bath to halt the cooking process. Pull off the top shell and remove the gills. Pick the meat from the body, legs and claws and set aside.
Bash remaining crab shells with a rolling pin and place in a frying pan along with the whole prawn, shells and heads over medium heat. Pour in olive oil and fry for five minutes. Add chicken stock and simmer for 15-20 minutes.
Cook sausage in a saucepan over a high heat for five minutes until fat starts to render out. Remove and set aside.
Sprinkle flour in same saucepan and stir until a roux forms. Add onion, capsicum and celery and cook for five minutes until golden. Add bay leaf, thyme, garlic, cayenne pepper and Tabasco. Stir through
Strain broth through a fine sieve into saucepan, discarding solids, and stir well to combine. Add tomato, crab meat, prawns and fish and cook for a further two minutes, or until fish is cooked through. Drizzle with lemon juice, season with salt and pepper and garnish with parsley.