Demand for salmon is soaring and is driving expansion of aquaculture—fish farming. For years, environmentalists advised conscientious consumers to avoid farmed salmon, but that's starting to change, thanks to an evolving industry.

Rich in protein and heart-healthy omega-3 fatty acids and low in saturated fats, salmon is increasingly being marketed as a healthy food. Demand for salmon has risen more than 20 percent in the last decade. Consumption is three times what it was in 1980.

That voracious appetite is increasingly being supplied by aquaculture, which now provides 70 percent of the global salmon market (2.4 million metric tons). In 2013, the largest market for farmed salmon, the United States, consumed 353,000 tons of the fish.

About five years ago, global aquaculture