Parasite acquisition by the invasive Chinese sleeper (Perccottus glenii Dybowski, 1877) (Gobiiformes: Odontobutidae) in Latvia and Ukraine.
The Perccottus glenii is one of the most invasive of European fish species. During August-September 2019, we examined Chinese sleeper from six waterbodies in Latvia and Ukraine for parasites. Seventeen parasite species were registered, including two ciliate species, one coccidia, one monogenean, one cestode, six trematodes, three nematodes, one acanthocephalan, one parasitic copepod, and one bivalve glochidia. Maximum species richness was registered in Ukraine, with eight species at Vylkove and three species at Lake Kartal. Numbers in Latvia were generally lower with three species at Ilgas and just one at Gailezers. The parasite fauna registered in Latvia was poor overall, the richest site being the University pond. Two non-native parasite species were registered, the monogenean Gyrodactylus perccotti and the copepod Neoergasilus japonicus. Gyrodactylus perccotti was observed in Lake Kartal and the Danube delta in Ukraine, but not in Latvia, while N. japonicus only occurred in the University Pond in Latvia. This is the first record of this species in Latvia. Low parasite acquisition by the Chinese sleeper in Latvia may be caused by the release of this fish from aquaria, which is commonly registered in the region. It is likely that such low parasite loads have contributed to the formation of stable populations and the subsequent increase in expansion.