Clean the fish and rinse it with salted water. Marinate the fish with 2 tablespoons fish sauce (30 ml), 1 teaspoon sugar (5 grams), 1 teaspoon vegetable bouillon powder (5 grams; I use this type because it doesn't contain MSG and is suitable for vegetarian cooking), and sliced onion. Let it marinate for 10 minutes to absorb the flavors.

While the fish is marinating, chop the tomatoes, cabbage, and celery. Add about 4 cups water (1 liter) to a pot and bring to a boil. Add the fish along with the marinade and let it boil for a few minutes.

Add the tomatoes and vegetables, season to taste, then turn off the heat. Transfer to a bowl and sprinkle with dill, onion, and black pepper. Enjoy a delicious, aromatic bowl of dill fish soup.