Step 1: Understanding the Concept:
Exotic fish species are introduced for aquaculture to increase production.
In local markets, they are often given regional trade names to attract consumers.
Step 2: Detailed Explanation:
The red-bellied pacu (Piaractus brachypomus) is an exotic freshwater fish native to South America.
It was introduced to India and is extensively cultured due to its fast growth rate and tolerance to high stocking densities.
In local Indian fish markets (especially in West Bengal, Andhra Pradesh, and Bihar), it is widely sold under the trade name "Roopchand" (or Rupchanda).
Step 3: Final Answer:
The fresh water fish Pacu is commonly called Roopchand, which corresponds to option (C).