Background. In Europe, the western tubenose goby, Proterorhinus semilunaris (Heckel, 1837), is the smallest and one of the most expansive species among invasive Ponto-Caspian gobies. The aim of the presently reported study was to investigate reproductive parameters of the tubenose goby population from the Vistula River, as one of the biological traits that might facilitate its successful invasion. Materials and methods. Fish were sampled monthly from March through October and the following parameters were determined: sex ratio, gonadosomatic index (GSI), fecundity (absolute, relative, batch), oocyte size distribution, and body condition (Fulton’s and Clark’s indices). Results. GSI varied considerably between sexes and between individual spring months. The increase of GSI and oocyte diameter distributions indicated that spawning of P. semilunaris in the Vistula River lasted from the end of April till July. Multimodal oocytes distribution during reproductive season suggested at least two or three spawning events. The absolute fecundity ranged from 504 to 1250. The mean batch fecundity (± standard deviation) was 338.35 ± 89.22. Both, the absolute and batch fecundity, but not the mean oocyte diameter in the batch, were related to the female standard length. The highest values of Fulton condition index were observed in the reproductive period compared to pre- and post-spawning, while Clark condition index showed a different pattern. Conclusion. The western tubenose goby displays reproductive strategy typical for other fish invaders that successfully naturalized in central Europe.

sex ratio, GSI, fecundity, body condition