Fish stock is made in the same way as meat stock in that the fish bones, heads and tails (and the shells of shellfish) are simmered in water with vegetables and flavorings. But fish stock is cooked for only 20-30 minutes as lengthy cooking will make it bitter. Once the stock has been strained it can be concentrated by further boiling. A glass of dry white wine added to the stock improves the flavor considerably.
After straining, the stock can be boiled slightly to reduce it to a more intensely flavored fumet. Fumet can be used in fish sauces, soups and stews. Court bouillon is the liquid used for poaching fresh fish such as salmon. It is made from water, white wine (or lemon juice or vinegar) and flavorings, but unlike fish stock, it does not contain any fish trimmings. Court bouillon is rarely featured in the finished dish.
** Making Stock