Wash the fish, dab dry and sprinkle with lemon juice. Peel onion, wash tomato and dice finely. Defrost crabs, if necessary, and rinse briefly.
Cook the pasta in boiling salted water for 8-10 minutes until al dente
Season fish with salt and pepper. Turn in 2 tsp. flour. Heat oil in a coated pan. Fry the fish for 2-3 minutes on each side. Take out and keep warm
Fry the onion in hot frying fat. Stir in tomato paste. Sweat curry first, then flour. Stir in milk and 2 tablespoons of water. Simmer for about 3 minutes. Season with salt, pepper and sugar
Add the prawns and tomato to the sauce and heat for about 3 minutes. Drain the pasta. Serve with fish fillet and crab sauce. Garnish with lemon and tarragon if desired