Peel, rinse and drain potatoes; Cut them into chunks.
Rinse and drain Chinese celery; Pull off leaves; Trim coarse stems off; Slice off the tough bask; Cut the remaining stems into sections.
Rinse and drain tomatoes; Tweeze off any stems; Cut the tomatoes into wedges.
Hold a golden threadfin bream 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; Rub the seasoning mixture into the fish evenly; Wrap the fish with baking paper completely.
Add 2 tbsp oil and the ginger into a nonstick casserole; Stir-fry it over a high heat till fragrant; Turn to a low heat; Arrange the golden threadfin breams into the casserole; Pan-fry them over a low heat till both sides are golden brown; Set the fishes aside; Turn off the heat; Pat-dry the fishes with kitchen paper; Set the oil aside.
Pour 1920ml water into the casserole; Bring to the boil over a high heat; Add all the ingredients; Bring to the boil over a high heat again; Cook over a high heat for 20 minutes; Cover the casserole with its lid; Cook over a low heat for 1 hour; Stir seasonings into the soup; Turn off the heat; Arrange it in serving bowls; Ready to serve.