Make 3-4 diagonal slices along each side of the fish. Sprinkle the cavity of the fish with salt.
Bruise the lemongrass with a back of a knife and fold up and place into the cavity of the fish.
Mix the stock with the garlic, Thai chillies, lime juice and light soya sauce. Place the fish on a plate and pour the chilli lime mixture over the fish.
When the steamer is ready, place the fish and plate into the steamer. Steam until the fish is cooked, about twenty minutes. You can check for doneness by inserting a knife along the backbone. If the meat pulls off the bone, it is done.
To serve, place the fish on the plate in the center of the table for all to enjoy. Spoon the broth left on the plate over the fish to make it glisten. Serve with jasmine rice.