Non-native Ponto-Caspian Gobies in the mouths of the Vistula River tributaries

Abstract

At present, four non-native gobiid species (racer goby Babka gymnotrachelus, monkey goby Neogobius fluviatilis, round goby Neogobius melanostomus and western tubenose goby Proterorhinus semilunaris) are listed as occurring in the Vistula River of Poland. In this work, the distribution and densities of gobiids in the river-mouth stretches of the Vistula tributaries flowing downstream from the Włocławek Reservoir in the Baltic Sea direction are presented. The fish were collected by electrofishing from a boat or while wading. Non-native gobiids were noted in 15 of the 18 tributaries studied. Among the 1,075 gobies caught, the western tubenose goby was the most common and occurred in 15 of the sites examined. The racer goby was registered in seven of the tributaries, while the monkey goby was recorded in only three. No round goby was caught. The highest densities of the western tubenose goby and racer goby were noted in the small stream located directly downstream from the Włocławek Reservoir. Among the species identified, the western tubenose goby seems to be more eurytopic because it was the last of these species to invade the Vistula River, but it is now the most widespread. In addition to a morphological identification of the fish, samples of each species were confirmed by an analysis of subunit I of the cytochrome oxidase (COI) barcode sequences. The genetic analysis of the COI subunit revealed that this sequence is effective for the taxonomic differentiation of the Ponto-Caspian gobies occurring in Poland. The results showed that gobiids have become a permanent element of the ichthyofauna of the Vistula and its tributaries that are available for migration Key words: invasive species, Gobiidae, Neogobius fluviatilis, Babka gymnotrachelus, Proterorhinus