Fish

Fish (lat. Pisces) is a paraphyletic group (according to the modern cladistic classification) of aquatic vertebrates. An extensive group of jawed-stomes, which are characterized by gill breathing at all stages of the postembryonic development of the organism. Fish live in both salty and fresh waters, from deep ocean trenches to mountain streams. Fish play an important role in most aquatic ecosystems as part of the food chain. Many species of fish are used by humans for food and therefore are of great commercial importance.

Modern fish range in size from 7.9 mm (Paedocypris progenetica) to 20 m (whale shark).

There are 35,768 species of fish known in the world (as of 2020), but new ones are constantly being described - about 300-500 species new to science are described every year. About 3,000 species live in Russia, including more than 280 species found in fresh waters.

The section of zoology, ichthyology, is devoted to the study of fish.