For some, unagi is just a punch line from Friends. But in Japan, this freshwater eel is a delicacy (100,000 tons are eaten every year). And in New York City, it’s a bona fide trend with two all-eel restaurants that opened last winter, Unagi and Hachibei. Though unagi is tasty, its boom is concerning, as freshwater eel is considered endangered due to a population decline. If you decide to try the trend, always ask whether the eel is sustainably farmed. If not, stick with the salmon!