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Fish

Sterlet

Acipenser ruthenus

Sterlet

General Overview

The Sterlet is **THE SMALLEST STURGEON**, yet **FREQUENTLY FOUND** in the Danube - one of the common sturgeon species in Central Europe! **UNIQUE** among Romanian sturgeons: **EXCLUSIVELY FRESHWATER FISH, POTAMODROMOUS** (lives and reproduces only in the Danube, does NOT enter the sea!). Extremely rare to descend into the sea - only stray specimens at the mouths of the Danube. Graceful, aerodynamic body - "the most spectacular fish in our waters"! Elongated head terminates with a long nose (significant individual variation). Medium mouth adapted for bottom feeding, lower lip **crested in the middle** - diagnostic feature against the ship sturgeon! **4 long FRINGED barbels** reach the upper lip. 12-17 large dorsal scutes. VERY small eyes - minor orientation role. Prefers: large flowing waters, deep, clear, hard bottom (rocky/clayey), well-oxygenated. **CANNOT tolerate turbid, oxygen-poor waters!** In Romania: Danube, Mures, Somes rivers. **VULNERABLE (VU)!** **Total prohibition 2006-2026!** Meat and roe highly prized. Artificial reproduction (aquaculture) for caviar and gelatin. Record: 4-11 year old specimens commonly caught. Consumes Palingenia longicauda larvae (mayfly) - delicacy! Spring reproduction (April-May), river migrations upstream.

Physical Characteristics

The smallest sturgeon! Graceful, aerodynamic body. Elongated head terminating with long nose (significant individual variation!). Medium mouth below head, lower lip crested in the middle - diagnostic feature vs ship sturgeon! 4 fringed, long barbels - smoothed reach the upper lip (characteristic compared to other sturgeons!). Very small eyes - minor orientation role. 12-17 large dorsal scutes. Large, powerful ventral fin; dorsal fin close to tail. Variable coloration. Typical dimensions: 40-50 cm, 4-5 kg. Maximum: 1-1.25 m, 16 kg.

Habitat & Distribution

Unique: exclusively freshwater fish, potamodromous! Lives and reproduces only in large rivers - does not enter the sea (extremely rare stray specimens at the mouths of the Danube)! Pontic-Caspian and Arctic basin. Through canals has penetrated large lakes (Ladoga, Onega). In Romania: Danube (main!), Mures, Somes. In Danube backwaters - only incidental. Prefers: large flowing waters, deep, clear, hard bottom (rocky/clayey), well-oxygenated. Cannot tolerate turbid, oxygen-poor waters! Typically stays deep in pits from which banks/shoals follow (after river bends). Migrations upstream before reproduction.

Behavior & Diet

Specialist benthic carnivore: insect larvae (dominant!), crustaceans, small snails, plant debris from sand/silt/stones. Delicacy: Palingenia longicauda larvae (mayfly) - highly prized! Juveniles and adults consume almost the same food type. Dominant organisms: Hydropsyche ornatula (42.2%), mayfly larvae. Large specimens consume small fish fry. Hunt in small groups year-round on the river bottom. Form large schools only during hibernation and reproduction. Relatively early maturity: 3-6 years. Records: 4-11 year old specimens commonly caught.

Life Cycle & Reproduction

Maturity: 3-6 years (relatively early for a sturgeon!). Spring reproduction (April-May). River migrations upstream. Reproduction on rocky bottom in current. Adhesive eggs. Moderate prolificacy. Artificial reproduction systematic in aquaculture since the 1970s! No parental care. Moderate growth. Longevity 26-27 years. Oldest specimen captured: 23 years (northwestern Black Sea - exception, normally does not enter the sea!).

Conservation Status

Vulnerable (VU) - Vulnerable! Less endangered than beluga, Russian sturgeon, starry sturgeon (CR) but still protected! Total prohibition 2006-2026 by Order 545/715/2016! Threats: (1) Dams - habitat fragmentation, (2) Pollution - sensitive to turbid/oxygen-poor waters, (3) Illegal fishing for meat/caviar/gelatin, (4) Habitat destruction. Advantage: exclusively freshwater - not affected by marine issues! Aquaculture: artificial reproduction for caviar and gelatin. Accidental capture - mandatory release, reporting! One of the more frequently encountered species in the Danube compared to other sturgeons!

Sources

  • IUCN Red List: Vulnerable
  • Wikipedia: Sterlet
  • FishBase: Acipenser ruthenus
  • Sturgeon conservation projects Romania