Cold (or hot) Curried Fish Soup

You really need a blender for this tasty, creamy soup. It is very cheap to make because you only need to use coley, almost the cheapest of fish, for the basis of it I think it is worth getting a few peeled prawns to add at the end. If by any chance you have an enterprising greengrocer, fresh coriander leaves, chopped up and thrown on at the last minute are a very special addition.