Step 1: Understanding the Concept:
Identifying the native distribution of commercially cultured exotic species is important for understanding their ecological preferences and biosecurity risks.
Step 2: Detailed Explanation:
The whiteleg shrimp, Penaeus vannamei (also known as Litopenaeus vannamei), is the most widely cultured shrimp species globally.
It is native to the Eastern Pacific Ocean, extending from Sonora in northern Mexico down through Central and South America to northern Peru.
Step 3: Final Answer:
Thus, its native region is the Eastern Pacific Ocean, which corresponds to option (C).