Fish are the largest group of vertebrate animals, with over 25,000 species identified so far. While some species mature at barely ⅖ of an inch long, others, such as whale sharks, grow to a length of 40 feet or more. One type of fish or another has colonized nearly every aquatic habitat that can be imagined, from desert pools that reach temperatures of 104°F (40°C) to the frigid seas of Antarctica. You never quite know what to expect from these thoroughly captivating creatures.

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