You can make a tasty fish head curry ( is that close enough to soup?)
by browning an onion, add garlic and ginger, chilies tomatoes, tumeric (1/4
teaspoon?)and garam masala (1-2 tablespoons). in coconut oil. when the oil
floats up to the top, add your whole fish heads fry 1-2 minutes and then add
some water. Simmer for about 1 hour or until everything melts together.
i hope that this is helpful. i can't be more specific because my mom-in law
always makes it for us. but this is how she does it. make sure you add
plenty
of minced garlic and minced ginger. These are the important  ingredients.
let me know how it comes out.
choti