Heat the oil in a saucepan large enough to hold all the ingredients. Add the onions and garlic and sauté gently for 5 minutes. Add the crushed dried chillies and mix well.
Add the squid, mussels, clams and king prawns and stir well.
Add the stock, wine, saffron, tomatoes, bay leaf and sugar and season with salt and pepper. Cover the pan and simmer gently for 5 minutes. Discard any mussels or clams that do not open.
Add the red mullet or sea bass and simmer for a further 5 minutes, then serve at once with a green salad.