"Sharks, skates, shrimp, seahorses and 30,000 other fishes swim through the world's waterways. With that much variety, you just have to ask: what makes a fish a fish? This book helps answer the question! Filled with amazing X-rays, full-color photographs and lively text, it looks at underwater creatures inside and out. Inspired by a popular Smithsonian exhibition and the first children's book to feature these extraordinary X-rays."--Publisher's description.