Peel the onion and garlic, finely chop the onion into thin strips and sauté with garlic in olive oil. Add orange zest and fish stock, bring to a boil again and simmer for 8 minutes at low heat.
Rinse fish, pat dry, cut into bite-size pieces, add to the soup and leave for 4 minutes. Season with orange and lime juice, salt and pepper. Chop parsley finely and garnish soup before serving.