Cut off the tail and head of the fish, then cut the body lengthwise along the spine, exposing the bones.
In a medium stockpot, heat the olive oil and sauté the onion, fennel and garlic with the salt and pepper until the onions are translucent—about 5 minutes. Beginning with the liquids, slowly add all of the other ingredients, then add the prepared fish (including the head and tail). Bring to a simmer. Cover and gently simmer for 2 hours.
Adjust the salt and pepper to taste. Strain into another pot using a coarse sieve and discard the solids. Clean the original pot, then, using a fine sieve, strain the liquid back into the cooking pot, again discarding the solids. Stock is good for 4 days when refrigerated, or 1 year when canned.
To can (may be done the following day, if stock is covered and refrigerated overnight): Bring the stock to a simmer for at least 20 minutes. Carefully ladle the stock into jars using the hot-pack method with 1 inch of head space, then process with a pressure canner for 25 minutes at 10 pounds for a weighted gauge or 11 pounds for a dial gauge. After processing, cool, label and store the jars.