A slow-moving, bottom-feeding fish (family Acipenseridae) with a long body, smooth skin with lateral rows of large bony plates (scutes) along the sides, mouth on the underside of the head, and four barbels protruding from the upper jaw. Most are marine, ascending rivers to spawn, but some live only in fresh water. Several species are harvested for their roe, used to make caviar. There are four genera with 27 species found throughout Eurasia and North America.