The difference between bouillabaisse and any other fish soup lies in the combination of flavors beyond the seafood stock. A hint of saffron, an accent of zested orange, and a few sliced fennel bulbs and fronds bring out an essence from the seafood that would otherwise remain hidden. While they might seem simple, omit any one of these ingredients and the depth of flavor in your bouillabaisse will lose the complexity that earned it such a vibrant reputation.
My preference is a bouillabaisse with a small amount of tomato and generous amounts of fennel and saffron, so the recipe here reflects that. Feel free to experiment by adjusting the amounts of tomato, fennel, orange zest, and saffron to suit your own tastes. Ultimately, a balance of ingredients is the most important factor, as you're aiming for a soup with flavors like a symphony: all in tune but with each instrument only minutely recognizable. —Belle Année