The robust oval, spine covered body of a long-spined porcupine fish (Diodon holocanthus) is revealed in this X-ray image. To ward off predators, a porcupinefish inflates its body by pumping water into its stomach, transforming the fish into a round, rigid ball bristling with spines. Scientists in the Division of Fishes at the Smithsonian's National Museum of Natural History use X-ray images, like the one shown, to study the complex bone structure and diversity of fish without having to dissect or damage the specimen.
In 2012, the National Museum of Natural History hosted "X-Ray Vision: Fish Inside Out," a temporary exhibit that showcases fish evolution and diversity through 40 black and white X-ray images prepared for research purposes. See more photos from the exhibit.