Shrimp can be sold raw with heads and shells intact; raw with shells on and heads removed; raw and peeled; or peeled, cooked, and deveined. They are sold by the "count," which is the number of shrimp per pound (454g). Shrimp can be frozen individually (called IQF), or in blocks. Most shrimp sold in U.S. supermarkets and fish markets have been frozen and thawed. Shrimp are also available canned.
There are thousands of varieties of shrimp, but those we eat fit into two categories.
These tend to be medium to large in size. Types include white shrimp, pink shrimp, and brown shrimp--all of which have pink meat when cooked. Rock shrimp have sweet meat within shells that are difficult to peel. Freshwater shrimp (or Malaysian prawns) come from lakes and river deltas in Asia and can grow to weigh nearly a pound (454g).
These tend to be smaller, but have firmer, sweeter meat. Pacific ocean pink and Atlantic Northern pink shrimp are usually machine-peeled, cooked, and served as shrimp meat. Spot, sidestrip, and coon shrimp live in North Atlantic waters and are usually sold fresh.