Any of the ~25 species of large fishes that comprise the family Acipenseridae in the order Acipenseriformes. These fish are found in North Temperate Zone waters, where they are almost exclusively bottom-living and feed on organisms such as mollusks, worms, and larvae. The body has five rows of bony plates, of which one is situated dorsally, two laterally, and two ventrally. The snout is elongate, and there are four barbels on its lower surface; the mouth is ventrally located, and in the adult the jaws lack teeth. The skeleton is mainly cartilaginous.