The Sterlet (Ascipenser ruthenus) is a sturgeon which has adapted perfectly to living in freshwaters. It inhabits clear, clean and well oxygenated waters. In the Danube, the Sterlet can be found mainly in the areas near Brăila and in the Borcea Channel.

On average, a Sterlet measures between 60 and 70 cm and weights 4 to 5 Kg, but some specimens can measure up to 120 cm and weight around 8 to 10 Kg. The Sterlet has an oblong, almost cylindrical body. Its snout is long, sharp and curved upwards. Its head is cone-shaped, with an inferior mouth, which has 4 fringed whiskers. A Sterlet's body is covered with shields: 10 to 15 on its backside, 50 to 65 on its sides and 15 to 20 on its belly. The bigger ones are rhomb-shaped and the smaller ones are serrated. Its backside is a greyish brown, with green iridescences. Its sides are coloured in a lighter shade and its belly is a yellowish white.

Generally, the Sterlet feeds on crustaceans, worms and larvae. The places where it feeds are located at 6 to 8 m deep.

A female Sterlet reaches its sexual maturity at the age of 7 to 9 years, whereas a male reaches its sexual maturity at the age of 4 to 5 years. The Sterlet reproduces in the Danube, in areas with strong currents, at depths of 6 to 8 m. During the reproductive period, between April and June, when the temperature of the water reaches 12 to 17 degrees, the female Sterlet will lay between 15 000 and 135 000 eggs. The fish larvae appear after 4 to 5 days.

Frequently, the Sterlet will interbreed with a Russian Sturgeon, giving birth to a hybrid, which can be recognized by the large number of shields it possesses. The resulted hybrid – the Beluga – has a great commercial value.