Sturgeon (Acipenser) is a genus of 20 different fishes, of which some twenty different species are known, from European, Asiatic and North American rivers. They pass a great part of the year in the sea, but periodically swim into large rivers, some in spring to deposit their spawn, others later in the season for some purpose unknown; only a few of the species are exclusively confined to fresh water. None occur in the tropics or in the southern hemisphere.
In Russia the fisheries are of immense value. Early in summer the fish migrate into the rivers or towards the shores of freshwater lakes in large shoals for breeding purposes. The ova are very small, and so numerous that one female has been calculated to produce about three million in one season. The ova of some species have been observed to hatch within a very few days after exclusion. Probably the growth of the young is very rapid, but we do not know how long the fry remain in fresh water before their first migration to the sea. After they have attained maturity their growth appears to be much slower, although continuing for many years. Frederick the Great placed a number of them in the Garder Sea Lake in Pomerania about 1780; some of these were found to be still alive in 1866. Professor von Baer also states, as the result of direct observations made in Russia that the Hausen (Acipenser huso) attains to an age of from 200 to 300 years.
Sturgeons ranging from 8 to 11 feet (2.5 to 3.5 m) in length are by no means scarce, and some species grow to a much larger size.
Sturgeon are known bottom-feeders. Using their projecting wedge-shaped snout, they stir up the soft bottom, and then use their sensitive barbels to detect shells, crustaceans and small fishes, on which they feed. Since they have no teeth, they are unable to seize larger prey.
In countries like England, where few sturgeons are caught, the fish is consumed fresh, the flesh being firmer than that of ordinary fishes, well-flavored, though somewhat oily. The sturgeon is included as a royal fish in an act of King Edward II, although it probably but rarely graces the royal table of the present period, or even that of the lord mayor of London, who can claim all sturgeons caught in the Thames above London Bridge. Where sturgeons are caught in large quantities, as on the rivers of southern Russia and on the great lakes of North America, their flesh is dried, smoked or salted. The ovaries, which are of large size, are prepared for caviar; for this purpose they are beaten with switches, and then pressed through sieves, leaving the membranous and fibrous tissues in the sieve, whilst the eggs are collected in a tub. The quantity of salt added to them before they are finally packed varies with the season, scarcely any being used at the beginning of winter. Finally, one of the best sorts of isinglass is manufactured from the airbladder. After it has been carefully removed from the body, it is washed in hot water, and cut open in its whole length, to separate the inner membrane, which has a soft consistency, and contains 70% of glutin.
The twenty species of sturgeons (Acipenser) are nearly equally divided between the Old and New Worlds. The more important are the following:
- The common sturgeon of Europe (Acipenser sturio) occurs on all the coasts of Europe, but is absent in the Black Sea. Almost all the British specimens of sturgeon belong to this species; it crosses the Atlantic and is not rare on the coasts of North America. It reaches 12 ft (4 m) long, but is always caught singly or in pairs, so that it cannot be regarded as a fish of commercial importance. The form of its snout varies with age (as in the other species), being much more blunt and abbreviated in old than in young examples. There are 11″“13 bony shields along the back and 29″“31 along the side of the body.
- Acipenser gueldenstaedtii is one of the most valuable species of the rivers of Russia, where it is known under the name “OssÃ©tr” (?); it is said to inhabit the Siberian rivers also, and to range eastwards as far as Lake Baikal. It attains to the same large size as the common sturgeon, and is so abundant in the rivers of the Black and Caspian seas that more than one-fourth of the caviar and isinglass manufactured in Russia is derived from this species.
- Acipenser stellatus, the “Seuruga” of the Russians, occurs likewise in great abundance in the rivers of the Black Sea and of the Sea of Azov. It has a remarkably long and pointed snout, like the sterlet (below), but simple barbels without fringes. Though growing only to about half the size of the preceding species, it is of no less value, its flesh being more highly esteemed, and its caviar and isinglass fetching a higher price. In 1850 it was reported that more than a million of this sturgeon are caught annually.
- The sturgeon of the great lakes of North America, Acipenser rubicundus (today: Acipenser fulvescens), with which, in the opinion of American ichthyologists, the sea-going sturgeon of the rivers of eastern North America, Acipenser maculosus?, is identical, has of late years been made the object of a large and profitable industry at various places on Lake Michigan and Lake Erie; the flesh is smoked after being cut into strips and after a slight pickling in brine; the thin portions and offal are boiled down for oil; nearly all the caviar is shipped to Europe. One firm alone uses from ten thousand to eighteen thousand sturgeons a year, averaging 50 lb (23 kg) each. The sturgeons of the lakes are unable to migrate to the sea, whilst those below Niagara Falls are great wanderers; and it is quite possible that a specimen of this species said to have been obtained from the Firth of Tay was really captured on the coast of Scotland.
- Huso huso, the “Hausen” of Germany, is recognized by the absence of osseous scutes on the snout and by its flattened, tape-like barbels. It is one of the largest species, reaching the enormous length of 24 ft (7 m) and a weight of 2000 lb (900 kg). It inhabits the Caspian and Black seas, and the Sea of Azov, whence in former years large shoals of the fish entered the large rivers of Russia and the Danube. But its numbers have been much thinned, and specimens of 1200 lb (540 kg) in weight have now become scarce. Its flesh, caviar and air-bladder are of less value than those of the smaller kinds.
- The sterlet (Acipenser ruthenus) is one of the smaller species, which likewise inhabits both the Black and Caspian seas, and ascends rivers to a greater distance from the sea than any of the other sturgeons; thus, for instance, it is not uncommon in the Danube at Vienna, but specimens have been caught as high up as Ratisbon and Ulm. It is more abundant in the rivers of Russia, where it is held in high esteem on account of its excellent flesh, contributing also to the best kinds of caviar and isinglass. As early as the 18th century attempts were made to introduce this valuable fish into the Province of Prussia and Sweden, but without success. The sterlet is distinguished from the other European species by its ion and narrow snout and fringed barbels. It rarely exceeds a length of 3 ft (1 m).
- The family Acipenseridae includes one other genus, Scaphirhynchus, the shovel-head or shovel-nosed sturgeon, distinguished by the long, broad and flat snout, the suppression of the spiracles, and the union of the longitudinal rows of scales posteriorly. All the species are confined to fresh water. One of them is common in the Mississippi and other rivers of North America, the other three occur in the larger rivers of eastern Asia.