Cook the pasta in 3-4 l boiling salted water (1 teaspoon salt per litre) according to the instructions on the packet.
Drain the tuna. Rinse anchovies cold, dab dry. Peel and chop the garlic. Puree finely with tuna, anchovies, half the capers and the caper water in a tall mixing bowl with a hand blender.
Stir in sour cream and mayonnaise. Season to taste with salt, pepper and lemon juice.
Clean, wash, drain and chop the arugula. Wash mint, shake dry and chop coarsely. Drain the pasta. Mix with rocket, mint and tuna sauce. Sprinkle with remaining capers.