First record of the Danube sturgeon Acipenser gueldenstaedtii Brandt & Ratzeburg, 1833 in Al-Furat Lake, Syria: likely aquaculture escapees

This study documents three separate occurrences of the Danube sturgeon (Acipenser gueldenstaedtii; Actinopterygii, Acipenseridae) in Al-Furat Lake, Syria, marking the first recorded presence of this species in Syrian freshwater systems. A. gueldenstaedtii, commonly known as the Russian sturgeon, is listed as critically endangered on the IUCN Red List of Threatened Species. This status is due to severe population declines caused by overfishing (primarily for caviar), habitat loss, and the damming of rivers that disrupt their spawning migrations. Conservation efforts, including fishing restrictions and aquaculture, are in place, but wild populations remain at high risk. The specimens were observed on 8 October 2020, in November 2020, and on 13 November 2022. These records are likely the result of aquaculture escapees from Turkish freshwater systems. The three juvenile specimens do not indicate an established reproductive population of A. gueldenstaedtii in the lake. The presence of A. gueldenstaedtii in Al-Furat Lake is ecologically significant because it could indicate: a new invasive species threat to the Euphrates system, a rare expansion of a critically endangered species, and human-induced changes in freshwater ecosystems facilitating unexpected species movements. Further studies are needed to assess long-term ecological consequences.