Sprat (Sprattus sprattus) as a Possible Source of Invasion of Marine Predators with Contracaecum osculatum in the Southern Baltic Sea

Abstract

Sprat is one of the most important fish in the food webs of the open part of the Baltic Sea. It is a crucial element in the diet of predators, which include salmonid and gadoid fish, marine mammals and sea birds. Sprat might also be a source of parasitic invasion for piscivorous organisms. We evaluated the level of sprat invasion with zoonotic nematodes in the southern Baltic Sea (Polish EEZ) from two sampling periods (1987–1989–1990: 3511 fish examined; and 2015–2016: 180 fish examined). While there was no evidence for zoonotic nematode parasites in sprats sampled during the first period, or in those from 2015, we found larvae of the liver worm Contracaecum osculatum in sprat sampled in 2016 from the central off-shore area of the Polish EEZ. Together with other recent reports, this suggests that sprat recently may play a role as a transmitter of this parasite to piscivorous organisms in several areas of the Baltic Sea.