Morphology of the only known population of Kessler's gudgeon Romanogobio kesslerii (Teleostei: Cyprinidae) outside the Black Sea basin

The Kessler's gudgeon (Gobioninae) collected in 2009 from the San River at Sanok (Poland) has been described morphologically. This is the only known population outside of the Black Sea basin. For each fish, 35 biometric features of the body were measured. Selected meristic features were determined. Osteology was studied from cleared and stained specimens. The coefficient of variation for the body proportions ranges from 1.04% to 11.31% and its basic meristic formula was as follows: D III 7-8; A III 5-6; ll 41-44. The sensorial system was characterised by a connection of the canals: infraorbital with the supraorbital and the preoperculomandibular with the supratemporal; the presence of an opercular canal and a well developed supraorbital bone. In the branchial apparatus the presence of a 4(th) cartilaginous hypobranchial and the presence of a single sublingual bone was observed.