A virus called infectious salmon anemia is sweeping through Chile’s fisheries, bringing attention to the condition of the country’s third-largest export industry. On expansive salmon farms, fish are bred in crowded underwater pens. Fish poop and food pellets contaminate the water. As many as 1 million nonnative salmon escape each year, gobbling native species and traveling as far as Argentina. The fish are treated liberally with antibiotics, some of which are prohibited for use on animals in the U.S. — but 29 percent of Chilean exports end up in American grocery stores. Salmon farming was welcomed as an economy-booster two decades ago, but in the wake of the virus, some in the industry are leaving in search of more pristine waters. Says one local fisherman, who says salmon farming has affected the quality of wild fish as well: “They bring illnesses and then leave us with the problems.”