In a large glass or ceramic bowl whisk together the harissa, coconut milk, lemon juice, lime juice and orange juice. Add the sea bass, onion, ginger, olive oil, preserved lemon, caraway seed, cumin and chervil. Stir to blend, then press everything down so there is a layer of liquid covering the top.
Cover and refrigerate for at least 3 hours or until the fish is opaque and white. Season with salt and add more harissa if desired before serving.