The National Zoo's carousel is among dozens that Carousel Works has installed around the U.S., each made to fit in with its surroundings. James Clark/NPR hide caption

itoggle caption James Clark/NPR

The New England Aquarium traded 800 mackerel for 12 puffins. OnceAndFutureLaura/Flickr hide caption

itoggle caption OnceAndFutureLaura/Flickr

Planet Money

A Dozen Puffins Will Get You 800 Mackerel: Inside The Weird Economy Of Zoos

Zoos and aquariums almost never buy or sell animals. But trade is thriving.

Listen Loading… 4:33
  • Playlist
  • Download
  • Embed
    Embed <iframe src="http://www.npr.org/player/embed/347659683/347873352" width="100%" height="290" frameborder="0" scrolling="no">

In this image from video provided by the Smithsonian National Zoo, Mei Xiang gives birth to a cub two hours after her water broke Friday. A second cub born Saturday was stillborn. AP hide caption

itoggle caption AP

Dennis Kelly (right), director of the Smithsonian's National Zoo, and Suzan Murray, chief veterinarian, discuss the panda cub's death. Mark Wilson/Getty Images hide caption

itoggle caption Mark Wilson/Getty Images

A composite of images from the panda cam, showing Mei Xiang during and after giving birth. National Zoo/Xinhua/Landov hide caption

itoggle caption National Zoo/Xinhua/Landov