1. Steam the fish fillet with the spring onion and ginger for 8 minutes. Discard the spring onion and ginger, flake the fish.
2. Dress the crab and shell the prawns. Rinse the seafood, drain well.
3. Bring stock to the boil, lower seafood and cook for 5 minutes. Then add the fish and the corn kernels.
4. Bring the soup back to the boil again, thicken with the cornstarch solution to the right consistency. Season to taste with a little salt and pepper. Then stir in the lightly beaten egg white. Garnish with coriander and serve immediately.