Cut the hydrated cod into 2-inch by 2-inch pieces. In a large pot of cold water, add the carrot, celery, and onion. When the water begins to simmer, add the cod pieces and cook for about 5 minutes, or until the cod begins to flake. Once cooked, remove the skin and any odd bone you may find. Break up the cod and place in a salad bowl with the olives, parsley, olive oil, and salt, to taste. Mix well. Let the salad rest in the refrigerator or serve immediately.
Ready-to-use hydrated cod can be found at most fish shops. However, if you choose to buy dry-salted cod, soak it in a large bowl of cold water for 2 days, changing the water 3 to 4 times a day. This will re-hydrate the cod and ensure that it is not too salty.