sturgeon beluga
   The sturgeon is a genus of ganoid fishes of the family Acipenseridae. They are large, sluggish fishes, some reaching a length of over 10 ft., and live on small ani­mals and plants which they suck in, the mouth being protractile and without teeth. The body is long and narrow with five rows of bony shields. The tail is heterocercal, having the upper lobe much larger than the lower. About 25 species are recognized, all inhabitants of fresh waters and seas in northern regions. All supply valuable commodities. for which they are regularly captured on a large scale. The great Russian "beluga" or "huso", Acipenser huso, once abundant in the Danube, Volga, and other large rivers emptying into the Black and Caspian seas, has furnished most of the salted roe called caviar, although some comes from the small sterlet. A. ruthenus, of the same region. The air bladder is also utilized for making isinglass.
   The common sturgeon, A. sturio, of the coasts and rivers of Europe and northeastem America, has been known to weigh 500 pounds. The largest of American sturgeons is that of the Pacific coast, A. transmontana;. called "white" in comparison with the rare "green" sturgeon, A. medirostris. The stur­geon of the Great Lakes, A. rubicundus, and the shovelnose of the Mississippi valley are characteristically American species. Fossil sturgeon remains have been found in rocks as old as the Eocene. Earlier less specialized ancestral forms are Chondrosteus of the Jurassic and the associated genus Gyrosteur. known only by fragments that indicate for it a length of 20 to 25 ft; and perhaps also the still older Palceoniscus of the Permian and Chierolepis of the Upper Devonian.