You could use other types of fish but I prefer salmon because it has a nice color, a really nice taste and has its own Omega 3 fatty acids. If you wish to use a white fish that is not so oily, you may want to add some olive oil. For the salmon I feel there is no need to add any extra oil at all. It will only spoil the dish. Also if you did have a fish head to add it to the cooking, you may want to remove this gently when soup finished cooking, or just before serving it.