Rinse dried Chinese yam under running water; Soak it in water for 3 hours; Remove and drain it.
Rinse dried prickly water lily seeds under running water; Soak them in water for 30 minutes; Remove and drain them.
Rinse dried lotus seeds under running water; Soak them in hot water for 10 minutes; Remove, drain and core them.
Rinse and drain dried goji berries.
Rinse, drain, peel and slice ginger.
Hold a flathead fish firmly by the head and scrape the scales from the tail towards the gills with a fish scaler; Rinse the fish under running water; Insert the knife into the anus near the tail; Draw the knife toward the head, splitting the fish to the base of the gills; Spread the abdominal cavity with fingers; Reach in and pull out the entrails; Rinse the cavity under running water; Cut off the head with the knife; Rinse the fish under running water again; Pat-dry the fish with kitchen paper.
Fill a pot with 2.5L water; Add the dried lotus seeds, the dried prickly water lily seeds and the dried Chinese yam; Bring to the boil over a high heat; Turn to a low heat; Cover the pot with its lid; Cook over a low heat for 1 hour.
Add 2 tbsp oil to a non-stick pan; Add the ginger and stir-fry it over a high heat till fragrant; Turn to a low heat; Arrange the flathead fish into the pan; Turn to a high heat; Pan-fry the fish over a high heat till both sides are slightly brown; Turn off the heat; Transfer the fish together with the ginger into the soup from the step 7; Bring to the boil over a high heat again; Turn to a low heat; Cover the pot with its lid again; Cook over a low heat for 1 hour; Add the goji berries; Cook over a low heat for 30 minutes; Stir seasonings into the soup; Turn off the heat; Arrange the soup in serving bowls; Ready to serve.