Peel, devein and remove the tails from the shrimp.
Bring a large pot of water to a boil, and drop in the shrimp.
Cook just until shrimp turn pink, about 3 minutes.
Immediately remove shrimp with a slotted spoon to a bowl of ice water to stop the cooking process.
Drain the water from the shrimp and pat dry.
In a large glass bowl, whisk together the chilled V8 or Clamato juice with the ketchup.
Stir in the chopped cilantro leaves.
Gently add in the avocado, stirring just until combined. Cover the bowl with plastic wrap.
Chill in refrigerator for at least one hour before serving.
Ladle servings (about 2/3 cup) into chilled wine glasses or parfait glasses.
Garnish with slices of lime and reserved shrimp, if desired.