with the fish heads, cut straight from the middle and split in half, put your fingers behind the eye balls and pop them out,
heat the pot little bit of oil, chuck the heads in add some carrot, salary, onion (chopped), sautee and add white wine, or sherry, or brandy, pour some water and boil, reduce heat let it simmer for half an hour, strain and use it for your green curry instead of the water, and its called fish stock,