Range expansion of Ponto-Caspian mysids (Mysida, Mysidae) in the River Tisza: first record of Paramysis lacustris (Czerniavsky, 1882) for Hungary

In the River Tisza, the longest tributary of the Danube, Limnomysis benedeni Czerniavsky, 1882 had been the only mysid recorded until recently. In 2011, we found a few juvenile specimens of Hemimysis anomala G. O. Sars, 1907 in two daytime samples taken from the Hungarian river section. During the overnight survey in 2012 aimed at revealing the actual distribution of this nocturnally active species, its most upstream occurrence was detected at Szolnok (river km 334). Paramysis lacustris (Czerniavsky, 1882) was also found at every sampling site of the river downstream of Tiszabercel (rkm 568), representing the first record of the species for the fauna of Hungary, and its most upstream self-sustaining population in the basin of the River Danube (1759 rkm from the Danube mouth). P. lacustris is the fourth Ponto-Caspian mysid that has begun to expand its range spontaneously in the Danube catchment after L. benedeni, H. anomala, and Katamysis warpachowskyi G. O. Sars, 1893. Due to its zooplanktivory it can be anticipated to have a considerable effect on the composition and abundance of the zooplankton assemblages and it may also become an important food source for certain fish species, especially in the impounded reaches and in stagnant or slow-flowing backwaters. P. lacustris — similarly to H. anomala — shows a diel vertical migration, moving to shallow waters only by night, which calls for increased attention in order to reveal its possible future range expansions. Although the River Tisza itself is not connected directly to other river basins via canals, it may potentially contribute to the further spread of the species (e.g., via fish stocking).