Acipenser gueldenstaedtii
The Russian sturgeon is **the second most economically valuable sturgeon** after the beluga. A benthic marine anadromous fish from the Black and Caspian seas, migrating in spring to the Danube for reproduction. **3 geographical races**: *A. g. colchicus* (Black Sea), *A. g. gueldenstaedtii* (northern Caspian), *A. g. persicus* (southern Caspian). Thick body near head, narrowing toward tail, covered with 10-20 dorsal, 30-50 lateral, 10-15 ventral plates. Short snout slightly vertically compressed, inferior mouth with 4 fringed barbels. Coloration varies by habitat: marine specimens more intense than Danube specimens; typically grayish-yellowish on sides/back, white-yellowish on abdomen. **CRITICALLY ENDANGERED (CR)!** **Total fishing prohibition 2006-2026!** Tasty flesh, dark gray roe highly prized (Osetra caviar). Threats: dams, poaching, pollution (hormonal imbalances, hermaphroditism!). **Restocking program**: 2014-2025 - 10,000-95,000 tagged fry released annually into the Danube (Borcea, Stelnica, Isaccea). Longevity 50 years.
Massive, fusiform body with 5 longitudinal rows of bony scutes (plates): 1 dorsal (9-18 scutes), 2 lateral (24-50), 2 ventral (6-13). Short, blunt snout — diagnostic characteristic! Inferior mouth with fleshy lips, 4 short barbels without fringes. Cartilaginous skeleton. No typical scales. Coloration: brownish-grey back, lighter flanks, yellowish-white abdomen. Typical dimensions: 1-1.5 m, 20-40 kg. Maximum: 2.3 m, 115 kg. Age: 40-50 years.
Anadromous species. Lives in the Black Sea, Azov Sea and Caspian Sea — primary marine habitats. Reproductive migrations into rivers: Danube (principal!), Rioni, Dnieper, Ural, Volga, Kura. In the Danube ascends several hundred km upstream for reproduction. The Iron Gates I (1972) and II (1984) dams blocked access to upstream reproduction habitats! Today reproduction in the Danube is extremely limited. Prefers hard substrates (rocky/sandy), moderately flowing, oxygenated waters. Overwinters at sea on deep bottoms.
Benthic carnivore: feeds on the river and sea bottom with molluscs (bivalves, snails), crustaceans, worms, insect larvae, small fish. Adults consume predominantly bivalve molluscs. Anadromous migratory behaviour: enters the Danube from the sea in spring (March-May) for reproduction, returns to sea after spawning. Some specimens remain in the Danube during winter. Forms groups (schools) during migrations. Maturity: males 12-14 years, females 14-18 years. Reproduction interval: every 2-4 years.
Sexual maturity: males 12-14 years, females 14-18 years. Spring spawning (April-May) on rocky bottom with current. Female deposits 60,000-1,300,000 grey-black eggs, 3-4 mm. Adhesive eggs on gravel. High fecundity. No parental care. Hatching after 5-10 days. Larvae drift downstream to sea in the first months. Slow but steady growth. Longevity 40-50 years. Does not reproduce every year — interval of 2-4 years between spawnings.
Critically Endangered (CR) — dramatic population collapse! From historical catches of hundreds of tonnes, today almost zero in the Danube. Total fishing prohibition 2006-2026 by Order 545/715/2016! Main threats: (1) Iron Gates dams — blocking reproduction habitats, (2) Intense poaching for eggs (caviar gris), (3) Water pollution, (4) Habitat destruction. Rescue programme: LIFEBoat 4 Sturgeons (WWF, Galati University, ARBDD) — restocking with tagged fry, monitoring, living gene bank. Accidental capture — mandatory release and reporting!