Step by step

Once cooked, take out the whole fish and remove the fish meat from the skin and bones, than put this flesh back in the soup, and serve the soup with hot croutons.

To get a fish soup absolutely full of different flavours, you could buy yet more varieties of fish, like flatfish, maybe already cleaned and gutted.
Fish soup comes directly from the world of fishermen, who were used to using the less expensive and prized fish in making dishes such as this.