Ingredients: Fish stock commonly includes other aromatic ingredients like bay leaves, peppercorns, onions, and carrots. For fumet, bones, heads, and tails of fresh fish are what’s boiled down.
Flavor: The use of fish bones (and sometimes, heads and tails) adds considerably more flavor to fumet than what is achieved using fish meat alone. Because fumet can be more bitter, more time-intensive, and has a more concentrated flavor than fish stock, a little bit goes a long way. Fish stock is milder in flavor and more versatile.
Uses: Fish stock can be used in a wide array of dishes, depending on the desired results. It can simply be used as the base for soups and sauces or as an ingredient to impart a subtle seafood flavor to dishes such as risotto or stews. Fumet is mostly suitable as a base or main ingredient for sauces and soups.