Remove the fish from its bath and remove the fins, backbone and jaw bones, then fillet it and chop finely.
In a large saute pan, heat the olive oil over medium-high heat and add the onion, celery, parsley, and pepper flakes and stir over the heat for 5 minutes. Add the fish and stir well, then add the tomatoes, bell peppers, quince, and raisins and stir well. Season with salt and pepper and cook over high heat 10 minutes, until hot all the way through. Serve immediately.