Fish [fĭsh]

Cold-blooded vertebrates with gills and fins, living wholly in water.

Fish are amazing creatures, with some species dating back to the time of dinosaurs. A fish is a vertebrate (an animal with a backbone) which has adapted to life in the water. Scientists have identified almost 30,000 different species of fish of all shapes and sizes. The smallest fish is 7 mm (0.3 inches) long, and the biggest sharks can grow to 12m (40 ft) in length. By studying fish we can learn how humans are changing the environment, and we can discover how salmon can swim all the way to the ocean and travel hundreds of miles back to the stream in which they were born.

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