Sturgeon are large (up to 6 m and 1.5 t) long-lived, archaic fish. All 25 species of sturgeon and two species of paddlefish inhabit the coastal waters, rivers and lakes of the Northern Hemisphere. They feed on small animals and plants, and most migrate up-river to breed and spawn. Their late sexual maturity, up to 25 years for beluga sturgeon females, is one of the reasons for their vulnerability to over-fishing. Today, the largest populations of sturgeon are found in the Caspian Sea, with important populations also found in the Danube and Amur River basins.
Six species of sturgeons are native to the Danube River Basin, five are classified as either "Endangered" or "Critically Endangered", and one "Vulnerable" (Acipenser ruthenus) according to the 2004 IUCN Red List of Threatened Species (IUCN 2004). In fact, one of the five endangered species, the Atlantic sturgeon (Acipenser sturio), is already extinct in the Danube River Basin. The Danube sturgeons are:
* Beluga (Lat: Huso huso, Romanian: morun) - 6m, 1500kg
* Russian sturgeon (Lat: Acipenser gueldenstaedtii, Romanian: nisetru) - 3m, 500kg
* Starry sturgeon or Sevruga (Lat: Acipenser stellatus, Romanian: păstruga) - 2.2m, 54kg
* Fringebarbel sturgeon (Lat: Acipenser nudiventris, Romanian: bogzar) - 2.2m, 80kg
* Atlantic sturgeon (Lat: Acipenser sturio, Romanian: sip, viza galbenă) - 5m, 1000kg
* Sterlet (Lat: Acipenser ruthenus, Romanian: cega) - 1.25m, 16kg
Until the 19th century, giant Beluga sturgeon the size of a small bus migrated on Danube as far as Germany and were important mainstays for many communities. Today, this ancient fish is on the brink of extinction. Dams have cut off the sturgeon's migration routes. Diking and draining of 80% of the Danube's former floodplains has removed important spawning and feeding areas. Overfishing has taken its toll as well. Now projects to improve navigation on the Lower Danube threaten to destroy some of the last sturgeon spawning areas and migration routes. WWF is working with the International Commission for the Protection of the Danube River and the governments of Romania and Serbia to examine options for making the dams passable to sturgeon and other species, which could extend migration and habitats by 1,000 km up to Slovakia.
Sturgeon fishing and trade in the products is a very profitable business. Compared to other fishery activities it is often viewed as “gold-mining”. Caviar is the unfertilized eggs of sturgeons. For many gourmets, caviar, dubbed "black pearls", is a food delicacy without parallel. The three main traded species of sturgeon produce distinctive caviar: Beluga, Osietra (Russian sturgeon) and Sevruga (stellate sturgeon). The color and size of the caviar are influenced by the species and the stage of maturity of the roe. The most sought after and expensive caviar is from beluga, a gigantic fish that can live for 100 years.