Cook pealed potato with fish and head and shells of shrimps about 30 minutes (you can cut potato into pieces to fasten cooking). When done, remove shrimp shells, potato and fish from soup and drain the soup.
Clean the fish and mix with potato. Make puree out of fish and potato. When done, put puree into drained fish stock. Let it boil for minute or two.
Remove meat from shrimp tails and put them into soup. Add olive oil, lemon juice, parsley leaves and season with salt and pepper. Cook not more than 15 minutes. Serve hot.