Using your own fish trimmings, or those from your local fish market or butcher, wash the trimmings well.
Combine all the ingredients in a stockpot and add enough water to cover everything by about an inch. Bring everything to a boil over high heat then reduce the heat to low once the mixture has boiled. Skim off the foam that has risen to the top, then cover the pot and simmer for 20 minutes.
Remove the pot from the stove and strain the stock trough a sieve, discarding all solids. Refrigerate or freeze, using as necessary.