Shave fennel thinly with a knife or mandoline. If using endive, separate the leaves and cut lengthwise into spears.
Combine fennel, arugula, endive and orange segments in a bowl.
Stir together orange juice and marmalade to combine. Slowly whisk in olive oil and season vinaigrette to taste with salt and pepper.
Dress the fennel mixture with the vinaigrette and serve.
This is a great salad to serve with robust fish, such as halibut or trout.