Anisakids of seals found on the southern coast of Baltic Sea

Abstract

In the present study 5 grey seals (Halichoerus grypus), 3 common seals (Phoca vitulina) and 1 ringed seal (Pusa hispida) bycaught or stranded on the Polish Baltic Sea coast in years 2000-2006 were investigated for the infestation of parasitic anisakid nematodes. 749 of anisakids were found. The most common were: Contracaecum osculatum (59.3%) and Pseudoterranova decipiens (31.0%). There were also small numbers of Anisakis simplex (0.8%). After performing RFLP three sibling species were found. C. osculatum was identified as C. osculatum C, P decipiens was identified as P. decipiens sensu stricto and A. simplex -A. simplex sensu stricto. Nematodes found in seals were mostly in L4 and adult life stage -both of them were equal with some minor variations among the specimens. Sex ratio was also equal, but there was slight excess of males in some cases. There was a minority of L3 larvae belonging to A. simplex species (0.8%).

Host size-dependent anisakid infection in Baltic cod Gadus morhua associated with differential food preferences

“…These crustaceans become infected when they feed on nematode larvae released from the parasite eggs delivered by seal. A dominance of adult C. osculatum in Baltic grey seal stomachs was previously documented by Skrzypczak et al (2014) and Lunneryd et al (2015), and the increase of fish infections during the last decades may be caused by the rapidly expanding grey seal population (Haarder et al 2014). Several fish species are able to obtain infection when ingesting the first intermediate hosts, and the present field study documented that more than 10% of the Baltic sprat investigated was infected by up to 8 parasite larvae per fish, which is a higher infection level than previously reported.…”

“…This development has been noted during a period with a marked increase of the grey seal Halichoerus grypus population (Haarder et al 2014). These pinnipeds are final hosts for both C. osculatum and P. decipiens (Marcogliese et al 1996, McClelland 2002, Mattiucci & Nascetti 2008, Skrzypczak et al 2014, Lunneryd et al 2015. Eero et al (2015) suggested that heavy C. osculatum liver infections may partly explain the distress of the eastern population of Baltic cod, where juveniles (< 30 cm total length [TL]) perform successfully but larger cod (> 38 cm TL) show increased mortality.…”

Helmintofauna of turbot Scophthalmus maximus (Linnaeus, 1758) from the southern Baltic Sea including new data

“…In the southern Baltic, it has been noted in smelt Osmerus eperlanus (Linnaeus, 1758), flounder Platichthys flesus (Linnaeus, 1758), cod Gadus morhua (Linnaeus, 1758), herring Clupea harengus (Linnaeus, 1758), and in zander Sander lucioperca (Linnaeus, 1758) in the Vistula Lagoon (Markowski 1933, Janiszewska 1938, Studnicka 1965, Rokicki 1975, Rolbiecki 2003. It is worth adding that mammals are observed more often in the Baltic Sea area, including its southern part, which may result in an increased occurrence of typically marine parasites, including acanthocephalan C. semerme (Härkönen et al 1998, Skrzypczak et al 2014.…”

Excretory/secretory products of anisakid nematodes: biological and pathological roles

“…seals, sea lions, dolphins, whales [7, 10, 11] and/or piscivorous birds [12–14] and hatched larvae which are free-living until they are ingested by an invertebrate host (e.g. a crustacean) whereafter they are transferred to a teleost transport host by predation.…”

“…A number of genes encoding central immune factors have been partly conserved throughout evolution from invertebrates via fish to mammals, but the variation is high [34, 35] and thereby it should be expected that host evasion mechanisms in different animal groups differ. It has also been suggested that differences among life cycles of different parasite species and even sibling species [11, 36] may be attributed to the relative abundance and function of these bioactive molecules influencing host specificity [37]. …”