Bring a 5-qt pot of highly salted water to a boil. Prepare a medium size bowl with icy water. Add shrimp to boiling water and simmer until cooked through, about 3 minutes. With a slotted spoon or strainer transfer to icy water to stop the cooking. Drain, pat dry and coarsely chop.
Stir together Clamato, lime juice and cilantro, avocado and shrimp. Season with salt and pepper to taste.