1) Roughly chop the vegetables into chunks, keeping the entire fennel.
2) Place all of the vegetables in a stockpot and place the parsley, bay leaves and peppercorns on top.
Add the fish bones to the pot and cover the bones with water.
3) Place a lid on top and place it on the stove.
4) As the stock comes to the boil, remove the lid and turn it down to the lowest heat. Bring the vegetables up to the boil and let simmer for 20 minutes.
Take it off the heat completely and let it cool for 20 minutes before straining off the water.
You now have a fish stock for all fish sauces.