In a large stockpot, combine the tomatoes, cardamom, cloves, cinnamon, red pepper, curry powder, and lemongrass with 6 cups of water and bring to a boil. Reduce the heat and simmer 20 minutes.
Strain the broth. Add the fish to the broth and poach until opaque, about 10 minutes. Season with salt. Ladle into shallow soup bowls and garnish with the parsley.