Fish

With over 32,000 described fish species, the varieties are endless. Most bony fishes are cold-blooded, covered in scales and breathe using gills—but there are exceptions to all of these rules.  

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X-ray image of a winghead shark

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X-Rays of Fish Reveal Diversity

Scientists in the Division of Fishes at the Smithsonian's National Museum of Natural History use X-ray imaging to study the...