Wash the fish bones and place in a large saucepan with all the stock ingredients. Bring to the boil over high heat, then reduce heat to low and cook, skimming frequently, for 20 minutes. Turn off the heat and allow to stand for 10 minutes to allow the sediment to settle. Double strain the stock through a fine sieve and discard the solids. If the stock is still not clear, pass it through muslin. Return to a clean pan, season with salt and bring to a simmer.
Blanch the seafood and each of the accompaniments separately in the stock and set aside. If serving immediately, place a teaspoon of fish sauce in each serving bowl, divide the blanched ingredients among the bowls, pour over the stock and serve immediately. Alternatively, you can blanch everything beforehand, then reheat in the stock just before serving.