Prevalence and molecular identification of acanthocephalan parasites (Corynosoma spp.) in the Baltic herring (Clupea harengus membras) and great cormorant (Phalacrocorax carbo)

Abstract

Baltic herring (Clupea harengus membras) is one of the most abundant and commercially important fish species in the Baltic Sea. In the Archipelago Research Institute, a long-term monitoring program was established in 1984 with an intention to monitor herring’s reproductive health and changes in the population. In 2014, some of the herring were infected with acanthocephalans or thorny-headed worms of genus Corynosoma. Thorny-headed worms are intestinal parasites that occur in vertebrates. Their life cycles include an amphipod as the intermediate host and a fish as a paratenic host. Acanthocephalans of the genus Corynosoma mature in the intestines of mammals such as seals. Between the years 2014 and 2019 total of 7002 herring and 65 Great cormorants (Phalacrocorax carbo) were examined and acanthocephalans were collected. Their species were identified using DNA-analysis. The prevalence of the Corynosoma infections in herring increased from 2014 to 2018. The prevalence was higher in the Archipelago Sea than in the Bothnian Sea. Infected herring and cormorant individuals were generally larger than non-infected. DNA-analysis showed that three different Corynosoma species caused the infections in herring: C. semerme, C. strumosum and C. magdaleni. 26 % of the cormorants were infected and DNA-analysis showed that all the Corynosoma in cormorants represented species C. semerme.