The best fish to include in a light stock to be used for cream and butter sauces are sole, turbot, halibut, and trout. For fish soups and hearty stews, use whatever non-oily fish bones and heads you have: the fished already mentioned plus bass, grouper, snapper, haddock, etc. Despite what most cookbooks tell you, fish stocks should be brought to a boil as fast as possible so that the albumin coagulates and rises to the surface for skimming. Simmer for no more than 30 minutes or the stock will tasty "fishy" and stale. The vegetables have to be finely chopped so that they cook entirely in this short time, and the acid from the wine is necessary if you are to use the stock for making butter sauces, but add it only after the vegetables have given up most of their flavor (it impedes this process if added at the beginning). Any leftover stock can be frozen for up to a month.