The Fascinating World of Fish

Fishes were the first vertebrates, appearing 500 million years ago. Today, over 25,000 species exist. Fishes breathe using gills, which extract oxygen from water. They are ectotherms, meaning their body temperature varies with the environment. Fishes use fins for movement and have keen senses. Most hatch from eggs. There are various types, including sharks with cartilage skeletons and others with bony skeletons.

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