Simmer the cleaned whole fish in a pot of water with the prawn shells until cooked. Remove fish and let cool before separating the flesh from the bone. Flake the flesh in small pieces. Strain the stock and reserve.
Tear pieces of the salted fish away from any bones, add the softened dried shrimp and the flaked flesh of cooked fish and put in blender and mince till fine. Set aside.
Blend together the spice ingredients until fine, adding a little oil to make a paste.
Heat a little oil in a pot and fry the blended spice ingredients till fragrant. Add asam gelugor, lemongrass, a handful of polygonum leaves and stir.
Add in the reserved stock to the pot and stir the ingredients together and bring to boil for 10 minutes. After that, add the minced seafood, kerisik and coconut milk. Lower heat and stir frequently. Add salt and pepper to taste.
Cook until the sauce begins to thicken and just before serving, throw in the fresh prawns, making sure not to overcook it in the sauce.
Serve the gravy on top of the spaghetti and add garnish.