Danang, VietnamFrom the outside Nha Hang Lang Nghe, in Danang, looks like any other respectable restaurant in Vietnam. Tables are invitingly laid out in the shade of a lush garden, and festive traditional art lines attractive brick walls. Families laugh over hot pots, and businessmen clink glasses.

Yet the veneer of wholesome normality masks a dark truth: Critically endangered giant river fish are Lang Nghe’s signature dish. Although it’s illegal to sell them in Vietnam, signs at the entryway entice diners with photos of imperiled Mekong giant catfish (“tasty meat, rich in omega-3”) and giant barbs (“good for men”), while a video showing a 436-pound giant catfish being cooked and eaten plays on a screen inside. Advertisements on social media likewise