Place fish bones and heads in a large bowl and cover with cold water. Let stand 1 hour. Drain, then rinse fish under cold running water, washing away any large areas of blood, such as near spine. In a large pot, add olive oil and sweat together carrots, onions, fennel, garlic, salt on medium high heat. Deglaze with the wine, and cook for 2 minutes. Add water, bouquet garni and bring to boil. Add fish bones, heads and scraps, bring to a boil and cook on medium heat for 25 minutes. Skim off impurities that rise to the surface during cooking. Fish fumet should not boil longer than 25 minutes; it makes stock cloudy.