Sustainability is certainly not an issue with the common carp, which is farmed and fished in freshwater worldwide. Native to Asia, the species eventually made its way into Europe and was introduced in the 1800s to the United States, where it’s now considered an invasive species. Processing entrepreneurs in the Midwest are working to expand the market — and fishing effort — for the fish, which is in demand in restaurants and shops in urban Asian communities. The hardy carp was one of the world’s original farmed fish, raised as early as 500 B.C. in China, which still accounts for the lion’s share of farmed production. While not widely consumed in this country, the fish is popular in Asia and Europe, home to many strains of common carps. The main varieties include:Leather carp, which was bred to have no scalesMirror carp, which has scales only near the finsThe fully scaled common carpMarket size for whole carp ranges from 2 to 3 pounds, though they can reach more than 50 pounds.