Amongst the non-native Ponto-Caspian gobies that have invaded the Middle Danube is the monkey goby Neogobius fluviatilis (Pallas, 1814). Despite a strong specialization towards sandy substratum, revealed in a previous study, monkey goby is considered an invasive species and therefore should demonstrate great plasticity in its biological traits. The main aim of the present study was to evaluate the age and growth of a non-native population of monkey goby from the River Ipeľ in Slovakia. Six age groups (0 – V) were observed in the sample from the River Ipeľ (n = 165), with males demonstrating faster growth than females, which was reflected both in the smoothing cubic B-spline model and in the annual increment. The cubic B-spline model indicated a reverse Lee’s phenomenon, especially in males, which is likely to have arisen from the size selective mortality. Growth of invading monkey goby from the River Ipeľ was slower than that reported for the species’ native range. Together with other growth patterns, this may suggest (among other possible explanations) a greater allocation of resources to reproduction than to somatic growth, which is a life-history pattern typical for newly established populations of successful invaders.
The postcranial skeleton of the Ponto-Caspian endemic benthophilines Anatirostrum and Benthophilus show unique specializations within gobioid fishes. Precaudal and caudal vertebrae are reduced in numbers and the dorsal pterygiophore insertion pattern is modified. Pterygiophores, which support no spine or segmented fin ray, are present in the skeletons at the rear of the first dorsal fin and at the second dorsal fin origin. Because of the low number of vertebrae the second dorsal and anal fin pterygiophores of Anatirostrum and Benthophilus are displaced anteriorly. The pterygiophores that support the first spine of these two median fins are positioned opposite to each other.