Caviar is salted sturgeon eggs. Each female spawns thousands at a time and a 132-154 lb (60-70 kg) female common sturgeon (Acipenser sturio) may have as many as a million eggs in her ovaries. Fish with over two million eggs are not unknown. The black or dark-colored (gray or greenish) eggs are spherical, 2-3 mm in diameter, and weigh 1-2 centigrams each; they are rich in proteins (28%), fat (15%), phosphorus, and vitamins. The roe may weigh 22-44 lb (10-20 kg), quite enough for a banquet, given that 3.5 oz (100 g) of caviar leaves one very satisfied.
Evidently, the caviar that reaches our tables does not consist of fresh sturgeon spawn. First, the eggs are washed to remove an enveloping gelatinous substance, and then delicately salted (3-8% of the total weight). The most appreciated caviar is the malossol, a large-grained, lightly salted (3-4%) caviar, prepared in the winter. Sometimes, the caviar is pressed to make a paste. It is never actually preserved or sterilized, and therefore has to be pasteurized and kept at low temperatures in sterile containers. The containers are generally very small, as caviar has become a luxury that few can afford. It is normally served cold in chilled bowls and eaten with a teaspoon or spread on small pieces of toasted bread or blinis, a type of soft, salty bread characteristic of eastern Europe.
Only sturgeon eggs are true caviar, although the name is often given to similar products made from the eggs of other species of fish. The commonest are the roes of the common striped mullet (Mugil cephalus), and especially lumpfish roe from the sea hen (Cyclopterus lumpus), a scorpaeniform from the North Sea which spawns small (1-2 mm diameter), greenish eggs, which are often dyed black. Salmon (Salmo salar, Oncorhynchus) caviar is also produced and consists of large, characteristically red eggs (3-4 mm in diameter). In reality, caviar is a generic term originating from the Turkish word khavyar and can quite properly be applied to salmon, mullet, or lumpfish roe. On the other hand, in the case of genuine sturgeon caviar, the term caviar is too limited, because it is produced by several different species, each with their distinct roe and name.
Sturgeon are coastal fish found in the northern hemisphere north of the Tropic of Cancer (Palaearctic and Nearctic regions). Some species only inhabit continental waters, but most are anadromous (marine species that enter estuaries and rivers to spawn). Sturgeons and paddlefish form the only extant members of the Chondrostei, a group of fish with a partly cartilaginous, partly ossified skeleton and with characteristic bony scales along the body. The largest of all the sturgeons and the origin of the most appreciated caviar is the beluga (Huso huso), a enormous fish weighing up to a ton, although most individuals do not exceed 220 lb (100 kg). It spawns in the rivers that flow into the Caspian, Black, and Azov seas, but overexploitation has reduced numbers to such a point that it is now prohibited to fish this species in some areas where it was once common. It resembles the Kaluga sturgeon (H. dauricus), native to the Amur River in China. This species gives a dark gray, large-grained (3 mm diameter), and very tasty caviar.
All other sturgeon caviars come from species belonging to the genus Acipenser. The osetra sturgeon (A. guldenstadti), also native to the river basins that drain into the Caspian, Black, and Azov seas, gives a yellowish or greenish, high-quality caviar, similar to that produced by the common sturgeon (A. sturio). This species is now restricted to the Black and Baltic seas, but until the 1950s was found all along the Atlantic coastlines of Europe, as well as in the Mediterranean. Next in quality comes the small black eggs of sevruga sturgeon (A. stellatus), a smaller species with a similar distribution to A. guldenstadti. The Adriatic sturgeon (A. naccari) and A. nudiventris [=A. glaber] from the Caspian and Black seas and the Sea of Aral (if it still exists) complete the inventory of anadromous Palaearctic sturgeons.
There are also Nearctic--that is to say, American--sturgeons that produce good quality caviar, including the Atlantic sturgeon (A. oxyrhinchus) and the short-nosed sturgeon (A. brevirostris) from the Atlantic coast, the white or Oregon sturgeon (A. transmotanus) from the Pacific, and the green or Sakhalin sturgeon (A. medi-rostris) from the American, Chinese, and Japanese coasts and rivers of the Pacific. There are also a number of species that never leave continental waters. Among these are the lake sturgeon (A. fulvescens [=A. rubicundus]), found in the lakes and rivers of Canada; the Siberian sturgeon (A. baeri) from Siberian rivers and lakes; and the sterlet (A. ruthenus), native to the River Dvina, the Siberian Ob and Yenisei rivers, and the river basins of the Caspian and Black seas.
The majority of these sturgeon species are commercially fished, although there is no doubt that those species that give the best caviar are also the most coveted. The Iranian, Kazakh, and Russian fishing ports of the Caspian Sea (Astrakhan at the mouth of the Volga is the most important), as well as the Romanian and Bulgarian ports on the Danube, account for most of the world's caviar trade. The largest producer in terms of sheer quantity is Russia (15,000 tons/year in 1960, mainly from the sevruga sturgeon), although the most prized is Iranian caviar, especially the large golden eggs of the Imperial osetra caviar. In 1993, a kilo of this caviar cost around $1000, although the annual Iranian production of around 210 tons is very limited. Without a doubt, this is the most carefully handled 210 tons of the world's entire fish catch!