Planet Earth

The Inner Life of Fish Revealed… by X-Rays

These stunning images offer a look inside the world's largest collection of fish.

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Photo Credits: text by Andrew Moseman

Since the Smithsonian's National Museum of Natural History began to collect marine specimens in the middle of the 19th century, the set has grown extraordinarily. The National Collection of Fishes now holds about 3.5 million fish.

The Smithsonian's curators have gathered digital X-rays of their collection in the book Ichthyo: The Architecture of Fish, which also features essays by oceanographer Jean-Michel Cousteau, ichthyologist Daniel Pauly, Museum of Photographic Arts director Deborah Klochko, and photo researcher Stephanie Comer.

This image shows a hookjaw moray eel, also called Bayer's moray, which skulks around reefs in the waters of Southeast Asia and Oceania.

Before photography, illustrations done by hand were used to document the beauty of nature.

"In 1895 the discovery of R??ntgen rays, or X-rays, made it possible to capture the intimate inner workings of animals and objects on film," Comer and Klochko write in Ichthyo. More than a century later, X-rays are still providing us with magnificent images, like this one of a stingray.

The X-ray images make it obvious that animals live to eat. "We begin to see the body as an afterthought, following the mouth," ichthyologist Daniel Pauly writes in an essay in the book.

Determining how a creature ate, based on its teeth or jaw, is often speculative work. But sometimes an X-ray puts an animal's last meal right in front of your eyes--in the case of this hungry shark catfish, a few clams, which the catfish is adept at digesting.

The Smithsonian's library of images now includes around 20,000 different species of fish, providing an invaluable record of ocean biodiversity. These shrimpfish come from one of 13 different species in the family Centriscidae. Shrimpfish, also called razorfish because of their sharp snouts, reach about eight inches in length.

Blowfish, balloon fish, puffer fish, porcupine fish--whatever you want to call these aquatic animals, they bear an effective deterrent against predators. This X-ray image shows a porcupine fish in its defensive posture--filled with water or air and deploying sharp spikes--and then in its normal, relaxed state.

When inflated, the porcupinefish can reach twice its regular height, and some species are poisonous. It should come as no surprise that these odd creatures have few predators.

Oceanographer and filmmaker Jean-Michel Cousteau writes in the book that "90 percent of commercially harvested large fish species are gone from the sea as a result of overfishing... I am forced to conclude that we are doing everything in our power to eliminate fish from the sea."

Many kinds of seahorses are in danger, including the dwarf seahorse seen here, which is listed as "vulnerable."

"The radiographic images in this book largely follow scientific, not artistic, conventions," writes Lynne Parenti, the Smithsonian's curator of fishes. Indeed, each page contains one kind of fish, arranged from the simplest jawless fishes at the book's beginning to the most complex spiny-finned species at the end.

But Ichthyo's ghostly black-and-white images are an artistic achievement as well. As the Albert Einstein quote on one page says, "The most beautiful emotion we can experience is the mystical. It is the power of all true art and science."

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