Senegalese-Style Seafood Gumbo

In a large pot, combine the fish heads and bones with the stock, onion and 8 cups of water and bring to a boil. Reduce the heat to low and simmer for 20 minutes, skimming off any foam from the surface. Strain the broth into a large bowl.

Wipe out the pot and return the broth to it. Add the okra, oysters, dried shrimp, garlic, chiles and fish sauce and bring to a simmer. Cook over moderately low heat for 10 minutes, stirring occasionally. Add the snapper fillets, shrimp and palm oil and simmer until the fish and shrimp are just cooked through, about 4 minutes. Stir in the crab and cook for 1 minute, until heated through. Season with salt. Serve with rice.