1. Put the raisins and the hot water in a small bowl and leave until the water is absorbed. In a large pot of boiling, salted water, cook the spaghetti until just done, about 12 minutes. Drain the spaghetti.
2. Meanwhile, in a large nonstick frying pan, heat 1 tablespoon of the oil over moderate heat. Sprinkle the mackerel with 1/4 teaspoon each of the salt and pepper. Cook the fish until just done, 2 to 3 minutes per side for 1/2-inch thick fillets. Remove the fish and then wipe out the pan. When the fish is cool enough to handle, discard the skin and flake the fish.
3. In the same pan, heat 1 tablespoon of the oil over moderately low heat. Add the onion and cook, stirring, until starting to soften, about 3 minutes. Add the pine nuts and cook, stirring occasionally, until starting to brown, about 3 minutes. Add the raisins, mackerel, the remaining 3/4 teaspoon salt, and 1/4 teaspoon pepper. Cook until heated through, about 2 minutes. Toss the mixture with the spaghetti, the remaining 5 tablespoons olive oil, and the dill.
Variation: Spaghetti with Sardines and Pine Nuts: In place of the mackerel, add two 3 1/2-ounce cans of boneless, skinless sardine fillets, drained, to the pan for the last 2 minutes of cooking. Break the fillets into flakes with a spoon.
Wine Recommendation: The full-force flavors of this dish--from the sweet raisins and strong mackerel to the dill--need to be paired with a full-flavored, acidic white wine. Try a sauvignon blanc from northern Italy or New Zealand.