A recent record of Romanogobio antipai (Actinopterygii, Cyprinidae, Gobioninae) from the Danube River in Bulgaria

The Danube delta gudgeon, Romanogobio antipai, has been considered to be extinct because there were no reliable recent observations. The latest record confirmed by a voucher specimen dating from 1992. We report here on a specimen of R. antipai collected in 2016 in the Bulgarian sector of the Danube main stream using a bottom drift net at a depth of 8 m. The species determination is supported by morphological examination including discriminant and cluster analyses in comparison with three syntypes and five non-type specimens of R. antipai, samples of the R. kesslerii species complex and R. vladykovi. Romanogobio antipai most clearly differs from both R. kesslerii and R. vladykovi by proportional measurements (caudal peduncle depth, head width, eye horizontal diameter, and interorbital width), from R. kesslerii also by the number of scales above and below the lateral line (6 and 4, respectively, (vs. commonly 5 and 3), and from R. vladykovi, also by 8½ branched dorsal-fin rays (vs. 7½) and the vertebral caudal region longer than the abdominal vertebral region (abdominal+caudal vertebrae 19+21 or 20+21, vs. commonly 20+20 or variants with a caudal region shorter than the abdominal one). The possibility that R. antipai represents a deep-water cophenotype of either R. kesslerii or R. vladykovi, cannot be excluded. The new record demonstrates that R. antipai is still extant in the lower Danube but may be restricted to greater depths in the main channel and the deltaic branches