The United States is the world’s largest consumer of coral reef fishes for public and private saltwater aquariums, importing upwards of 11 million wild fish annually. The illegal and deadly use of cyanide, a stunning agent for easy fish capture, is widespread in major source countries. We are assessing the prevalence of cyanide exposure in the most popular species sold in the U.S. Gauging the magnitude of this illegal wildlife trade is a crucial first step toward effectively addressing it.