Put the fish trimmings into a large saucepan and cover with water. Add all the remaining ingredients, stir well and bring to the boil. Froth will rise to the top, when it does skim it off with a cold spoon. Lower the heat then simmer partially covered for about 40 minutes. Do not simmer longer than this or the stock will be bitter.
Remove the saucepan from the heat and strain the stock through a sieve. Discard everything left in the sieve then called, cover tightly and chill in the refrigerator used the stock within 2 days or you can freeze it for about 2 months