Rub the insides and outsides of the fish with salt, ginger and half the vinegar. Set aside to marinate for 1 hour.

Drain the fish and pat dry with kitchen towels.

Fill a large saucepan one-third full with vegetable oil and heat until it reaches 185°C (360°F) on a deep-fat thermometer, or until a small cube of stale bread dropped into the oil turns golden in 50 seconds. Arrange the fish in a deep-frying basket and carefully lower them into the oil. Fry for 5 to 6 minutes, or until they are crisp. Remove from the oil and drain on kitchen towels.

Put the fish in a large saucepan and pour over the boiling water. Crumble in the stock cube and add the remaining vinegar and the soy sauce. Bring to the boil, reduce the heat to moderately low and simmer for 5 minutes. Carefully stir in the remaining ingredients.

Transfer the soup to a warmed tureen and serve at once.