The Russian Sturgeon or the Danube Sturgeon (Ascipenser gueldenstaedtii) is a species of fish from the sturgeon family. Nowadays, the population of Danube Sturgeons from the Danube's Delta has decreased alarmingly.

The size of a Russian Sturgeon varies between 90 and 120 cm and its weight varies between 10 and 15 Kg. However, there have been spotted specimens with a size of 2, 5 m and a weight of 150 Kg.
The Russian Sturgeon has a short, round, wide and slightly vertical snout. Its mouth is inferior and its 4 fringed whiskers are located near its snout.
During its first years of life, the Russian Sturgeon feeds on various insect larvae, rain worms or crustaceans. As an adult it prefers polychaetes (annelid marine worms), black gobies, herrings or molluscs.

From a genetic point of view, the Russian Sturgeon is a special species. Generally, the sturgeons have a structure with 120 chromosomes; however, a Danube Sturgeon has 240 chromosomes.

When they migrate, the Russian Sturgeon gather in large groups. Their main migration is during spring, when they swim upstream to lay their eggs.
On the Danube, the Russian Sturgeon will reach the Iron Gates, where it will lay its eggs, in deep areas with sandy and rocky bottoms. During winter time it will stay in the Black Sea.
Its sexual maturity is reached late in its life and reproduction occurs only each 2-3 years, during April-May. A female can lay up to 3 million eggs.
The spawns appear after 4 to 5 days and they remain in the river waters until the end of July, when they migrate towards the sea, close to the river mouths.
They will remain here until they reach the age of 3. After this age they will retreat in the sea, in the areas with deep water.