Cook for about 8 minutes, or until the fish is opaque, adding the shrimp for the last 2 minutes of simmering time. Distribute the fish evenly among 6 or 8 bowls. Taste the broth for seasoning and pour over the fish. Squeeze a wedge of lime over each bowl and drop it in. Garnish with cilantro sprigs, if desired, and serve.
Dende oil is Brazilian palm oil, available in Latin American markets.
Be sure to get the Brazilian rather than the West African product, which is much heavier. Or use half the amount of the West African palm oil and substitute vegetable oil for the other half. The easiest way to grind them is in a coffee grinder, if you have one which is reserved for grinding spices.