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Prevalence of sealworm larvae (Pseudoterranova sp. (p)) in cod (Gadus morhua) in relation to length-groups of fish ((1) 40–54 cm, (2) 55–59 cm, (3) 60–69 cm, and (4) >70 cm), fish-age, and seawater depth.
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About 300 cod (Gadus morhua) were sampled on three different sites of different proximity to grey seals (Halichoerus grypus), which are the most important final host for Pseudoterranova krabbei, off Drangar, Northwest Iceland, in the summer of 2004. Cod caught at each station were grouped into four sizes: (1) 40–54 cm, (2) 55–59 cm, (3) 60–69 cm an...
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Citations
... However, during last decade the most abundant nematode in these fish species in the Baltic Sea is Contracaecum osculatum so colled liver worm [8,[11][12][13], reported also in sprat [14], great sandeel [15] and salmon [16] Pseudoterranova decipiens (named also codworm or seal worm) the rarest among listed nematode species, was found in cod [8] and shorthorn sculpin [17] from the Baltic Sea. 2 The life cycles of these nematodes are very similar, with marine mammals playing the role of final hosts [18,19], but there is clear host specificity: particular species of marine mammal are responsible for closing the life cycle of a particular parasite species. Thus, the final hosts for A. simplex are cetaceans, in the Baltic Sea represented by the harbor porpoise, Phocoena phocoena [20]; for C. osculatum, the final host is the grey seal, Halichoerus grypus [21]; and for P. decipiens, both the harbor seal, Phoca vitulina [22] and the grey seal [23] can adopt this role. In the final host, larval stage L4 transforms to the dioecious mature stage, which is capable of producing fertilized eggs. ...
... The dispersion of zoonotic Anisakidae nematodes among marine organisms of the Baltic Sea has been reported over the last decade [8,13,16] and is also observed in fish caught in Polish waters. It is in line with the growing population of the grey seal, which is the final host in the life cycle of C. osculatum [21] and P. decipiens [23], to over 40,000 individuals in 2020 for the whole Baltic Sea [58]. Studies on the presence of nematodes in Baltic Sea seals (H. ...
The zoonotic Anisakidae nematodes Anisakis sp., Pseudoterranova sp., Contracaecum sp. have been found in Baltic Sea fish species. In particular, there has been an alarming increase in the dispersion of Contracaecum sp. over the last decade, due to the growing number of grey seal (Halichoerus grypus) in the area. This marine mammal is also the final host in the Pseudoterranova sp. life cycle. The aim of our study was to summarize the presence of Anisakidae nematodes in the salmon (Salmo salar) and other commercially important fish species (cod, herring and sprat) from Polish marine waters. This was evaluated by parasitological inspection of the internal organs and body cavities of 89 individual salmon and the results were compared with infection levels in cod, herring and sprat. The presence of Pseudoterranova sp. is reported for the first time here in the muscle tissue of salmon from the Baltic Sea. In addition, we highlight the elevated levels of cod and sprat infection with Contracaecum sp. over the last decade. The presence of Anisakidae nematodes in commercially important fish species may have implications for human health since these parasites pose a risk of anisakidosis.
... However, there is some host specificity, and particular species of marine mammal are responsible for closing the life cycle of each parasite species. The final hosts for A. simplex are cetaceans, which in the Baltic Sea are represented by the harbor porpoise, Phocoena phocoena (Herreras et al. 2004); for C. osculatum, the final host is the grey seal, Halichoerus grypus (Fagerholm 1990), while for P. decipiens, it is the harbor seal, Phoca vitulina (Aspholm et al. 1995), and the grey seal (Hauksson 2011). In the final host, larval stage L4 transforms to the mature stage and fertilized eggs enter the aquatic environment in the host's feces. ...
... The widespread dispersion of Anisakidae nematodes in the Baltic Sea over the last ten years is related to the increasing number of marine mammals in the area, particularly the grey seal, H. grypus, which is well-documented as a final host in the life cycles of C. osculatum (Fagerholm 1990) and P. decipiens (Hauksson 2011). ...
Anisakidae nematodes, especially Contracaecum osculatum, Anisakis simplex, and Pseudoterranova decipiens, have dispersed throughout the Baltic Sea over the last decade. Despite the fact that salmon, Salmo salar, is a popular choice among consumers and therefore one of the most valuable Baltic fish species, information about the level of infection of salmon liver with these zoonotic nematodes is sparse. In 2020, a total of 120 salmon livers were inspected for the presence of parasites showing that 13% of salmon livers were infected with C. osculatum. Furthermore, a single Pseudoterranova sp. larva was detected in one salmon liver, representing a host-parasite system that has never previously been reported in the Baltic Sea.
... This increase has been linked to the growing grey seal population in the Baltic Sea, as this pinniped is the final host of both nematodes (McClelland 2002;Lunneryd et al. 2015;Mattiucci et al. 2017;Zuo et al. 2018). A corresponding association between larval nematode infections in cod and grey seal abundance was also recorded in Iceland (Ólafsdóttir and Hauksson 1998;Hauksson 2011), Norway (Jensen and Idås 1992;Aspholm et al. 1995) and Canada (Brattey et al. 1990;McClelland et al. 1990;Fowler and Stobo 2001;Marcogliese 2001;McClelland 2002;Fowler and Stobo 2011). A number of definitive hosts of anisakid nematodes have been recorded in Greenland waters. ...
Anisakid nematode larvae occur frequently in the liver of Atlantic cod, but merely few infection data from cod in waters around Greenland exist. The present study reports the occurrence of third-stage anisakid larvae in the livers of 200 Atlantic cod caught on fishing grounds along the West coast of Greenland (fjord systems of Maniitsoq) in May, June, August and September 2017. Classical and molecular helminthological techniques were used to identify the nematodes. A total of 200 cod livers were examined, and 194 were infected with third-stage nematode larvae (overall prevalence of infection 97%) with a mean intensity of 10.3 (range between 1 and 44 parasites per fish). Prevalences recorded were 96% for Anisakis simplex (s.l.), 55% for Pseudoterranova decipiens (s.l.) and 8% for Contracaecum osculatum (s.l.). Sequencing the mtDNA cox2 from 8 out of 23 these latter larvae conferred these to C. osculatum sp. B. A clear seasonal variation was observed, with a rise in A. simplex (s.l.) and P. decipiens (s.l.) occurrence in June and August and a decline in September. The study may serve as a baseline for future investigations using the three anisakids as biological indicators in Greenland waters.
... The high macroscopic similarity of anisakid nematodes, especially as larval stages, host mobility and the zoonotic potential necessitate an effective tool like the RFLP for correct species identification. Nematode infections in fish and decreasing fish health have been associated with recovering marine mammal populations by some authors (Jensen and Idås, 1992;Hauksson, 2011;Buchmann and Mehrdana, 2016). However, environmental and anthropogenic factors contributing to fish immunity such as salinity, temperature, prey availability and pollutant exposure from ammunition dumpsites have to be taken into consideration (Baršienė et al., 2014;Lang et al., 2017Lang et al., , 2018. ...
Harbour porpoises (Phocoena phocoena) are the only native cetacean species in the German North and Baltic Seas and the final host of Anisakis (A.) simplex, which infects their first and second gastric compartments and may cause chronic ulcerative gastritis. Anisakis simplex belongs to the family Anisakidae (Ascaridoidea, Rhabditida) as well as the phocine gastric nematode species Pseudoterranova (P.) decipiens and Contracaecum (C.) osculatum. These nematode species are the main causative agents for the zoonosis anisakidosis. The taxonomy of these genus with life cycles including crustaceans and commercially important fish is complex because of the formation of sibling species. Little is known about anisakid species infecting porpoises in the study area. Mature nematodes and larval stages are often identifiable only by molecular methods due to high morphological and genetic similarity. The restriction fragment length polymorphism (RFLP) method is an alternative to sequencing and was applied to identify anisakid nematodes found in harbour porpoises from the North Sea, Baltic Sea and North Atlantic to species level for the first time. In the study areas, five gastric nematodes from different harbour porpoise hosts were selected to be investigated with restriction enzymes HinfI, RsaI and HaeIII, which were able to differentiate several anisakid nematode species by characteristic banding patterns. Anisakis simplex s. s. was the dominant species found in the North Sea and Baltic porpoises, identified by all three restriction enzymes. Additionally, a hybrid of A. simplex s. s. and A. pegreffii was determined by HinfI in the North Sea samples. Within the North Atlantic specimens, A. simplex s. s., P. decipiens s. s. and Hysterothylacium (H.) aduncum were identified by all enzymes. This demonstrates the value of the RFLP method and the chosen restriction enzymes for the species identification of a broad variety of anisakid nematodes affecting the health of marine mammals.
... In the Baltic Sea, genetically distinct stocks of cod follow different migration patterns (Ovegård et al., 2012) and are therefore exposed to different infection risks (Lunneryd et al., 2015). Nursery areas for cod in the Baltic Sea are located in coastal waters (Bagge et al., 1994) and fish that stay near a coastline with a high seal density have a higher likelihood of infection (Hauksson, 2002(Hauksson, , 2011. The life cycles of A. simplex, C. osculatum and P. decipiens are similar and involve marine mammals as the final hosts (McClelland et al., 1990;Klimpel and Palm, 2011). ...
Cod (Gadus morhua), an important fish species in the Baltic Sea, is the paratenic host for many parasite species, including the zoonotic nematodes, Anisakis sp. and Contracaecum osculatum. We aimed to identify which invertebrate species (found in situ in the fish stomach) are responsible for infection of cod with zoonotic nematodes. We found that Crangon crangon and Gammarus sp., both invertebrate prey species of cod, were infected with Anisakis simplex and C. osculatum, respectively. These host-parasite systems are reported here for the first time, implicating C. crangon and Gammarus sp. as sources of infection of Baltic cod with zoonotic nematodes.
... The ecology of seals involves the formation of terrestrial colonies (some species also use pack ice) during the mating season, which are used as haul out sites 40 . In consequence, the concentration of the parasites' eggs should be high in areas where the definitive hosts aggregate [41][42][43][44][45] . A connection between the presence of pinniped colonies and the codworm burden in fish has been made ever since protective measures following commercial seal hunt led to the recovery of seal populations 46 . ...
Environmental niche modelling is an acclaimed method for estimating species’ present or future distributions. However, in marine environments the assembly of representative data from reliable and unbiased occurrences is challenging. Here, we aimed to model the environmental niche and distribution of marine, parasitic nematodes from the Pseudoterranova decipiens complex using the software Maxent. The distribution of these potentially zoonotic species is of interest, because they infect the muscle tissue of host species targeted by fisheries. To achieve the best possible model, we used two different approaches. The land distance (LD) model was based on abiotic data, whereas the definitive host distance (DHD) model included species-specific biotic data. To assess whether DHD is a suitable descriptor for Pseudoterranova spp., the niches of the parasites and their respective definitive hosts were analysed using ecospat. The performance of LD and DHD was compared based on the variables’ contribution to the model. The DHD-model clearly outperformed the LD-model. While the LD-model gave an estimate of the parasites’ niches, it only showed the potential distribution. The DHD-model produced an estimate of the species’ realised distribution and indicated that biotic variables can help to improve the modelling of data-poor, marine species.
... A third species, Anisakis simplex, can also be found in Baltic seals but merely as immature individuals, as the final hosts are cetaceans and not seals. Associations between seal abundance and anisakid infections of local fish stocks have been studied widely in other areas, including Icelandic (Ólafsdóttir & Hauksson, 1997(Ólafsdóttir & Hauksson, , 1998Hauksson, 2002, 2011), Canadian (McClelland, 2002 and Norwegian (Jensen & Idås, 1992; Aspholm et al., ...
Populations of grey seals ( Halichoerus grypus ), sprats ( Sprattus sprattus ) and cod ( Gadus morhua ) in the Baltic Sea are relatively stationary. The present work, applying classical and molecular helminthological techniques, documents that seals and cod also share a common parasite, the anisakid nematode Contracaecum osculatum , which uses seals as the final host and fish as transport hosts. Sequencing mitochondrial genes ( COX1 and COX2 ) in adult worms from seals and third-stage larvae from livers of Baltic fish (sprats and cod), showed that all gene variants occur in both seals and fish. Other anisakid nematodes Pseudoterranova decipiens and Anisakis simplex are also found in both seals and cod in the Baltic Sea, but at much lower rates. The Baltic grey seal population was left at a critically low level (comprising a few hundred individuals) during the latter part of the 20th century, but since the year 2000 a marked increase in the population has been observed, reaching more than 40,000 individuals at present. Ecological consequences of the increased seal abundance may result from increased predation on fish stocks, but recent evidence also points to the influence of elevated parasitism on fish performance. Contracaecum osculatum larvae preferentially infect the liver of Baltic cod, considered a vital organ of the host. Whereas low prevalences and intensities in cod were reported during the 1980s and 1990s, the present study documents 100% prevalence and a mean intensity of above 80 worms per fish. Recent studies have also indicated the zoonotic potential of C. osculatum larvae in fish, following the consumption of raw or under-cooked fish. Therefore the present work discusses the impact of parasitism on the cod stock and the increasing risk for consumer health, and lists possible solutions for control.
... During recent years the infestation by two different parasites, the cod worm residing in the cod flesh and the liver worm residing in the cod liver, has increased [18,34,35]. Seals are the final host in which the parasites produce their eggs [76], and therefore, it could be supposed that with an increasing grey seal population [77], the risk of cod infection would also augment [18,36,78]. In our models, seal abundance was the first variable eliminated by the model selection procedure when the analyses were conducted separately for the two time periods. ...
Investigating the factors regulating fish condition is crucial in ecology and the management of exploited fish populations. The body condition of cod (Gadus morhua) in the Baltic Sea has dramatically decreased during the past two decades, with large implications for the fishery relying on this resource. Here, we statistically investigated the potential drivers of the Baltic cod condition during the past 40 years using newly compiled fishery-independent biological data and hydrological observations. We evidenced a combination of different factors operating before and after the ecological regime shift that occurred in the Baltic Sea in the early 1990s. The changes in cod condition related to feeding opportunities, driven either by density-dependence or food limitation, along the whole period investigated and to the fivefold increase in the extent of hypoxic areas in the most recent 20 years. Hypoxic areas can act on cod condition through different mechanisms related directly to species physiology, or indirectly to behaviour and trophic interactions. Our analyses found statistical evidence for an effect of the hypoxia-induced habitat compression on cod condition possibly operating via crowding and density-dependent processes. These results furnish novel insights into the population dynamics of Baltic Sea cod that can aid the management of this currently threatened population.
... mentation for parasite-free status (EFSA, 2010). However, one of the reasons that the problem with worm infected fish products is increasing in certain geographic areas is associated with the increasing populations of marine mammals. Seal population sizes in Iceland were previously shown to be correlated with P. decipiens infections (Hauksson 2002; 2011). Similar associations were shown in Norway (Jensen and Idås, 1992) and recently grey seal population in the eastern Baltic sea has expanded significantly to around 50,000 individuals since the year 2000 leading to increased infections of P. decipiens and C. osculatum (Buchmann and Kania, 2012; Mehrdana et al., 2014; Horbowy et al., 2016). ...
The anisakid nematodes Anisakis simplex (Rudolphi, 1809), Pseudoterranova decipiens (Krabbe, 1878) and Contracaecum osculatum (Rudolphi, 1802) occur as third stage larvae in marine fish products and may infect consumers ingesting raw or under-cooked fish products. Clinical symptoms associated with the infection, termed anisakidosis, vary from irritation of the oesophagus and stomach, via nausea, vomiting and diarrhoea to severe epigastric and abdominal pain. Third-stage larvae of A. simplex are found in the body cavity, musculature and various organs, P. decipiens occur mainly in the fish musculature (fillet) and C. osculatum larvae reside predominantly in the liver, body cavity, mesenteries and pyloric caeca. Preventive measures, including mechanical removal of worms, heat treatment or freezing to kill worms, are needed in order to reduce the risk of human infections. The anisakid life cycle involves several hosts. A. simplex nematodes use cetaceans (whales) as final hosts whereas P. decipiens and C. osculatum have their adult stage in pinnipeds (seals). Eggs released by worms in these hosts pass with feces to seawater where free-living third-stage larvae hatch from the eggs. Various invertebrates – including euphausiids, copepods and amphipods – feed on these larvae, become infected and serve as intermediate hosts. A range of fish species may serve as transport hosts following ingestion of infected invertebrates and the final stage develops after two additional moults in the stomach of marine mammals which consumed infected fish. Control measures may be implemented to reduce infections of fish stocks and thereby risk of human infections.
... Nothobomolochus fradei is a little known but widespread parasitic copepod favouring clupeoid hosts (Ho & Lin 2004;Reed et al. 2012). The majority of publications in which Nothobomolochus fradei is mentioned are of taxonomic nature (Ho & Lin 2004;, 2011, only two reported prevalence figures Reed et al. 2012). While only 10% of the sardines (Sardinops sagax) examined by Reed et al. (2012) harboured N. fradei at low mean intensity, a very high yearround incidence and mean intensity was predicted for snoek, a sympatric, predatory gempylid. ...
Master's dissertation 2015 University of Cape Town
