A sturgeon is a very large fish that lives in rivers and seas in the colder parts of the northern world — Russia, the Caspian Sea, parts of Europe and North America. It looks ancient, because it is: sturgeon have hardly changed for many millions of years. Instead of ordinary scales, the body carries rows of bony plates, the snout is long and pointed, and the mouth points downward for feeding along the bottom. Some kinds grow longer than a person is tall and live for decades. The word matters to learners mostly because of one thing: caviar. The eggs of the sturgeon, salted, are caviar — the famous, very expensive food. So in reading you will meet the word mainly in three places: nature writing about the fish itself, food and luxury writing about caviar, and news about conservation, because heavy fishing has made several kinds of sturgeon endangered and trade in wild caviar is now tightly controlled. Like many fish names, the plural is usually the same as the singular: 'we saw three sturgeon'. 'Sturgeons' is possible, especially when talking about different species, but 'sturgeon' is safer. The word also names the meat of the fish, which is firm and often smoked.