First report of the Chinese sleeper Perccottus glenii Dybowski, 1877 in the Drava River, Croatia.
Chinese sleeper (Perccottus glenii) is one of the most successful invasive fish species, spreading rapidly to colonize a wide range of ecosystem types, from lentic oxbows to large rivers and freshwater lakes. Previously, only a single individualof P. glenii has been recorded from Croatian waters, in the Sava River catchment. This study reports the presence of additional record and the first populationof P. glenii in the Croatian part of the Drava River. During a field survey, eight individuals (n = 8) of P. glenii were collected from a shallow and overgrown freshwater oxbow in the Drava River flood zone, within a NATURA 2000 protected site. Since several individuals were within the mature size class (i.e., larger than 55 mm standard length), the results emphasize the importance of early confirmation of the presence of this invasive species, and the need for comprehensive biological surveillance of the Drava River and similar floodplain habitats, especially downstream of this collection site. Two hypotheses (north and south) explaining the arrival of Chinese sleeper into the Croatian part of Drava River are proposed. Semi-closed oxbows, such as the present one, could represent a suitable ecosystem for detailed in situ experiments on P. glenii ecology and migration patterns.