Make two marinades as follows: Place 1 cup of the olive oil and quarter cup of lemon juice in each of two bowls. Add the dill to the first bowl and the horseradish and mustard to the other. Add salt and pepper to both marinades. Cut the salmon, tuna and swordfish into half by half by 5 cm pieces. Place the salmon and the swordfish in the horseradish-mustard marinade and the shrimp and tuna in the dill marinade for about 30 minutes. While the seafood marinates, soak the bamboo skewers in cold water. Thread the seafood on the skewers, alternating fish, and beginning and ending with a shrimp. Grill over hot coals for about 2 minutes, turning occasionally. Makes 10 servings.