What is a Fish?

Fish are the most diverse group of vertebrates, with more species than amphibians, reptiles, birds, and mammals combined. They are aquatic vertebrates with a backbone and skull, distinguishing them from invertebrates like jellyfish. Fish are cold-blooded, unlike warm-blooded aquatic mammals such as whales and dolphins. Key adaptations include gills for respiration, paired fins for swimming, and protective scales. Most fish reproduce externally. These adaptations have enabled fish to dominate aquatic ecosystems worldwide.

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