Integrating Anisakis spp. parasites data and host genetic structure in the frame of a holistic approach for stock identification of selected Mediterranean Sea fish species

Variation in the levels of anisakid infection in the European anchovy Engraulis encrasicolus (Linnaeus) from the Bay of Biscay during the period 2000-2023 (ICES Subarea 8)

The European anchovy Engraulis encrasicolus is one of the most important commercial species in the Bay of Biscay (ICES Subarea 8), and our analysis focused on the analysis of the temporal mean abundance, prevalence, and intensity of Anisakis spp. larvae species in anchovies from ICES Subarea 8 in the years 2000, 2001, 2014-2016, and 2019-2023. Prevalence in adult individuals of anchovy was only 1% in 2000 but increased to 90% in 2014. Since 2015, the prevalence has decreased, and the number of individuals affected in 2023 accounted for 17.6%. The mean abundance showed a similar trend, with a peak of 3.79 nematodes/anchovy in 2014, falling to 0.21 in 2023. The species A. simplex sensu stricto and A. pegreffii were identified by PCR/SANGER sequencing and PCR/RLFP techniques in 2019 and 2020. Anisakis simplex (s.s.) was the most abundant species and, according to the results returned by these two techniques, it accounted for an average of 62.4% and 52.1% of total nematodes in 2019 and 2020, respectively. The results of studies monitoring infection levels in anchovies showed that the mean abundance and prevalence changed over the course of the study period and that the proportion of different species of Anisakis is also subject to variation from year to year.

An update and ecological perspective on certain sentinel helminth endoparasites within the Mediterranean Sea

The Mediterranean Sea is recognized as a marine biodiversity hotspot. This enclosed basin is facing several anthropogenic-driven threats, such as seawater warming, pollution, overfishing, bycatch, intense maritime transport and invasion by alien species. The present review focuses on the diversity and ecology of specific marine trophically transmitted helminth endoparasites (TTHs) of the Mediterranean ecosystems, aiming to elucidate their potential effectiveness as ‘sentinels’ of anthropogenic disturbances in the marine environment. The chosen TTHs comprise cestodes and nematodes sharing complex life cycles, involving organisms from coastal and marine mid/upper-trophic levels as definitive hosts. Anthropogenic disturbances directly impacting the free-living stages of the parasites and their host population demographies can significantly alter the distribution, infection levels and intraspecific genetic variability of these TTHs. Estimating these parameters in TTHs can provide valuable information to assess the stability of marine trophic food webs. Changes in the distribution of particular TTHs species can also serve as indicators of sea temperature variations in the Mediterranean Sea, as well as the bioaccumulation of pollutants. The contribution of the chosen TTHs to monitor anthropogenic-driven changes in the Mediterranean Sea, using their measurable attributes at both spatial and temporal scales, is proposed.

Phylogenetic and phylogeographic analyses of Anisakis simplex sensu stricto (Nematoda: Anisakidae) from the common minke whale in Korean waters

The genus Anisakis is among the most significant parasites to public health, as it causes anisakiasis, a parasitic infection in humans resulting from consuming raw or undercooked seafood. Although the infection status of i>Anisakis in second intermediate hosts, such as marine fishes and cephalopods, and humans have been severally reported in Korea, no information about the definitive host in Korean waters is available. In 2014, 2 adult gastric nematodes were collected from a common minke whale (Balaenoptera acutorostrata) found in the East Sea, Korea. These worms were identified as A. simplex sensu stricto (s.s.) by comparing the mitochondrial COX2 marker with previously deposited sequences. Phylogenetic and phylogeographic analyses of A. simplex (s.s.) worldwide revealed 2 distinct populations: the Pacific population and the European waters population. This is the first report on adult i>Anisakis and its definitive host species in Korea. Further studies on Anisakis infection in other cetacean species and marine mammals in Korean seas are warrantedi>Anisakis.

Anisakis infection in anchovies (Engraulis encrasicolus) from Iberian waters, southwestern Europe: Post-mortem larval migration

The Anisakis larvae presence in fish for human consumption is a health risk that needs to be monitored. The anchovy is a fish that is highly appreciated by consumers and that can harbour Anisakis. It is thus necessary to periodically evaluate the presence of anisakid larvae in them. So, anchovies from Iberian Peninsula coasts were analysed. Fish examination for macroscopic nematodes showed L3s of both Anisakis type I and Hysterothylacium aduncum. The Anisakis prevalence varies with the catching area and the fish size. The muscle prevalence was 7.45% (mean intensity 1.75; range 1-5). Molecular analysis showed 110 A. simplex s.s. (17 in muscle), 22 A. pegreffii (3) and 7 hybrid genotype individuals (1). Considering that most of the Iberian Peninsula coasts are a sympatry area between these two Anisakis species, it has been observed that A. simplex s.s./A. pegreffii ratio increases from south to north in a clockwise direction. Also, 19 larvae were detected on the fish surface from the Bay of Biscay, indicating the ability of these larvae to migrate after the fish death. The A. simplex s.s./A. pegreffii larvae proportion found on the anchovy surface is similar to the found in viscera and lower than in muscle, suggesting that most of the larvae migrating to the surface must have come from the visceral package. This confirms the importance of removing fish viscera immediately after capture, for those fish species where this is possible. As both species cause anisakiasis/anisakidosis, these data show a real risk to human health, especially in dishes highly prized in Mediterranean countries prepared with raw or semi-raw anchovies.

A century of parasitology in fisheries and aquaculture

Fish parasitological research associated with fisheries and aquaculture has expanded remarkably over the past century. The application of parasites as biological tags has been one of the fields in which fish parasitology has generated new insight into fish migration and stock assessments worldwide. It is a well-established discipline whose methodological issues are regularly reviewed and updated. Therefore, no concepts or case-studies will be repeated here; instead, we summarize some of the main recent findings and achievements of this methodology. These include the extension of its use in hosts other than bony fishes; the improvements in the selection of parasite tags; the recognition of the host traits affecting the use of parasite tags; and the increasingly recognized need for integrative, multidisciplinary studies combining parasites with classical methods and modern techniques, such as otolith microchemistry and genetics. Archaeological evidence points to the existence of parasitic problems associated with aquaculture activities more than a thousand years ago. However, the main surge of research within aquaculture parasitology occurred with the impressive development of aquaculture over the past century. Protozoan and metazoan parasites, causing disease in domesticated fish in confined environments, have attracted the interest of parasitologists and, due to their economic importance, funding was made available for basic and applied research. This has resulted in a profusion of basic knowledge about parasite biology, physiology, parasite-host interactions, life cycles and biochemistry. Due to the need for effective control methods, various solutions targeting host-parasite interactions (immune responses and host finding), genetics and pharmacological aspects have been in focus.

Anisakis Infection in the Spotted Flounder Citharus linguatula (Pleuronectiformes: Citharidae) Caught in the Gulf of Cadiz (Area FAO 27-ICES IXa) Appears to Negatively Affect Fish Growth

Spotted flounder (Citharus linguatula L.) caught in the Gulf of Cadiz (area FAO 27 ICES IXa) were examined for Anisakis larvae and to assess the possible risk of anisakiasis in humans through consumption of this fish. Larvae of the genera Anisakis and Hysterothylacium were identified in the analysis of 128 purchased fish specimens. All Anisakis larvae corresponded to type I. Molecular analysis showed the presence of A. pegreffii, A. simplex s.s., and recombinant genotype between the two. The prevalence of Anisakis was 9.4% with a mean intensity of 1.42, while for Hysterothylacium the values were 12.5% and 1.06. The length and weight of the fish, but not Fulton's condition factor, varied significantly between infected and uninfected fish. The prevalence of Anisakis increased with fish length, with no fish parasitized with Anisakis measuring less than 15.5 cm (2-2.5 years old), which is probably related to the reported dietary change of these fish at around 2 years of age. Fish not parasitized with any of these nematodes showed positive allometric growth, while those parasitized only with Anisakis showed negative allometric growth. When comparing both groups including only fish ≥ 15.5 cm (the smallest size of Anisakis-infected fish), the difference is shown to be statistically significant (p = 0.01), suggesting that Anisakis infection of spotted flounder negatively affects fish growth even when parasite intensity is low, which may have important economic repercussions. Finally, the low prevalence and, above all, intensity of Anisakis in these fish, as well as the habit of consuming this fish fried in oil in our geographical area, means that the risk of acquiring anisakiasis through consumption of this fish is low.

Demographic history and population genetic structure of Anisakis pegreffii in the cutlassfish Trichiurus japonicus along the coast of mainland China and Taiwan

Studying the genetic diversity of nematode parasite populations is crucial to gaining insight into parasite infection dynamics and informing parasite phylogeography. Anisakiasis is a zoonotic disease caused by the consumption of infectious third-stage larvae (L3) of Anisakis spp. carried by marine fish. In the present study, a total of 206 mitochondrial DNA sequences (cytochrome c oxidase 2, cox2) were used to study the genetic diversity, genetic structure, and historical demography of twelve A. pegreffii populations from Trichiurus japonicas along the coast of mainland China and Taiwan. Two distinct evolutionary lineages of A. pegreffii and no significant genealogical structures corresponding to sampling localities suggested that isolation in the marginal seas shaped their patterns of phylogeographic distribution along the coast of mainland China and Taiwan during glaciation with lower sea levels. Furthermore, pairwise F_ST values and AMOVA did not indicate any significant genetic differentiation among groups with no relation to the geographic area, which might be attributed to fewer barriers to gene flow as well as large population sizes. The results of the neutrality test, mismatch distribution, and Bayesian skyline plot analyses showed that entire population underwent population expansion during the late Pleistocene. Analysis of the demographic history revealed that A. pegreffii underwent historical lineage diversification and admixture due to secondary contact based on ABC analysis. The present research represents the first definitive population structure and demographic history across sampling locations of A. pegreffii along the coast of mainland China and Taiwan.

Hybrid Genotype of Anisakis simplex (s.s.) and A. pegreffii Identified in Third- and Fourth-Stage Larvae from Sympatric and Allopatric Spanish Marine Waters

Simple Summary

The nematode species Anisakis simplex sensu stricto (s.s.) and Anisakis pegreffii are wormlike parasites found in commonly consumed fish and are the main cause of human anisakiasis. Outwardly, the two nematodes are extremely similar and difficult to distinguish, especially in their larval forms. Genetic analysis has discovered the existence of a hybrid between these two “sibling species”, but its identification is a controversial matter, as results differ according to the specific region of the DNA analysed. The aim of our work was to confirm the presence of this hybrid genotype in fish off the Spanish coast and to obtain fourth-stage larvae in the laboratory to study if different genotypes are associated with different growth behaviour. Our results confirm that hybrid genotypes can be overestimated if identification is based on a particular molecular marker. We also obtained fourth-stage larvae with a hybrid genotype, which has not been reported previously. These findings are valuable for the taxonomic classification of Anisakis species, and for further epidemiological and biomedical research.

Abstract

The sibling species Anisakis simplex (s.s.) and Anisakis pegreffii are parasites of marine mammals and fish worldwide and the main causative agents of human anisakiasis. In sympatric areas, a hybrid genotype between the two species has been identified, mainly in third-stage larvae, but rarely in fourth-stage and adult forms. The aim of this study was to confirm the presence of hybrid genotypes in larvae parasitizing fish caught in sympatric and allopatric Spanish marine waters, the North-East Atlantic and West Mediterranean, respectively, and to study possible differences in the growth behaviour between genotypes. Of the 254 molecularly analysed larvae, 18 were identified as hybrids by PCR-RFLP analysis of the rDNA ITS region, 11 of which were subsequently confirmed by EF1 α-1 nDNA gene sequencing. These results therefore indicate an overestimation of hybrid genotypes when identification is based only on the ITS region. We also report the detection of a hybrid specimen in a host from the West Mediterranean, considered an allopatric zone. Additionally, fourth-stage larvae with a hybrid genotype were obtained in vitro for the first time, and no differences were observed in their growth behaviour compared to larvae with A. simplex (s.s.) and A. pegreffii genotypes.

Species composition and infection levels of Anisakis (Nematoda: Anisakidae) in the skipjack tuna Katsuwonus pelamis (Linnaeus) in the Northwest Pacific

Parasites can be used as biological tags to assess stock structures in various marine fish species. In the present study, the species composition and infection levels of parasitic nematodes of the genus Anisakis in the skipjack tuna Katsuwonus pelamis were examined in the Northwest Pacific and adjacent seas. A total of 867 third-stage larvae of Anisakis were collected from 112 skipjack tunas captured around Japan and in other subtropical localities. All larvae were identified as A. berlandi, A. pegreffii, A. simplex (s.s.), A. typica, and A. physeteris (s.l.) by the direct sequencing of the mitochondrial cox2 gene and real-time PCR assays targeting the nuclear ITS region. Anisakis species composition differed among northeastern Japan, the Sea of Japan, and other areas (central Japan, the Nansei Islands, and subtropical region), which is largely concordant with previous stock discrimination of skipjack tuna. Molecular phylogenetic analysis resulted in two intraspecific genetic groups in A. simplex (s.s.), one of which occurred almost exclusively in northeastern Japan. This could be a useful indicator for stock discrimination. Skipjack tunas from northeastern Japan were also characterized by a remarkable variety in the intensity of A. simplex (s.s.), suggesting the commingling of individuals with different migration patterns. This idea might be further justified by the geographic distribution of two genetically distinct groups of A. physeteris (s.l.).

Molecular Identification of Zoonotic Parasites of the Genus Anisakis (Nematoda: Anisakidae) from Fish of the Southeastern Pacific Ocean (Off Peru Coast)

The study aims to perform, for the first time, the molecular identification of anisakid larvae in commercial fish from the Southeastern Pacific Ocean off the Peru coast, and to provide data on their infection level by fishing ground, fish host, and site of infection. Fish specimens (N = 348) from the northern and the central coast of Peru were examined for parasites. The fish fillets were examined by the UV-press method. Anisakis spp. larvae (N = 305) were identified by mtDNA cox2 sequences analysis and by the ARMS-PCR of the locus nas10 nDNA. Two hundred and eighty-eight Anisakis Type I larvae corresponded to Anisakis pegreffii, whereas 17 Anisakis Type II larvae clustered in a phylogenetic lineage distinct from Anisakis physeteris deposited in GenBank, and corresponding to a phylogenetic lineage indicated as Anisakis sp. 2, previously detected in fish from both Pacific and Atlantic waters. Anisakis pegreffii was found to infect both the flesh and viscera, while Anisakis sp. 2 occurred only in the viscera. The average parasitic burden with A. pegreffii in the examined fish species from the two fishing grounds was significantly higher than that observed with Anisakis sp. 2. The results obtained contribute to improve the knowledge on the distribution and occurrence of Anisakis species in Southeastern Pacific waters and their implications in seafood safety for the local human populations.

New Parasite Records for the Sunfish Mola mola in the Mediterranean Sea and Their Potential Use as Biological Tags for Long-Distance Host Migration

Studies describing the parasite fauna of sunfish species from the Mediterranean Sea are to date limited, despite information gained through parasitological examination may reveal unknown ecological and biological aspects of both hosts and parasites. Moreover, recent molecular studies on sunfish taxonomy revealed the presence of two species belonging to the genus Mola in the Mediterranean basin, namely M. mola and M. alexandrini. These two fish taxa have long been synonymized or confused among them, which implies that the majority of the studies carried out so far reported the parasites infecting both species under a single host species, generally referred to as M. mola. We hereby investigated the parasite fauna of a 43 cm long M. mola specimen from the Mediterranean Sea, whose identification was confirmed by molecular tool, and provided the first evidence of the occurrence of the nematode Anisakis simplex (s.s.) and of the cestode Gymnorhynchus isuri in Mola species anywhere. The use of helminth species as biological tags for the sunfish is also discussed.

Anisakis and Hysterothylacium species in Mediterranean and North-East Atlantic fishes commonly consumed in Spain: Epidemiological, molecular and morphometric discriminant analysis

The consumption of raw fish parasitized with larval ascaridoid nematodes of the family Anisakidae can cause anisakiasis, provoking gastrointestinal and/or allergic symptomatology. The main causative agents in the Anisakis genus are the sibling species Anisakis simplex sensu stricto (s.s.) and A. pegreffii of the A. simplex sensu lato (s.l.) complex. Larvae of A. simplex (s.l.) are frequently detected in fish commonly consumed in Spain, as are larvae of the genus Hysterothylacium of the family Raphidascarididae, associated with allergic reactions but not considered pathogenic. Reported here are the results of an epidemiological survey of ascaridoid larvae in three commonly consumed fish species in Spain, horse mackerel (Trachurus trachurus) (n = 52), blue whiting (Micromesistius poutassou) (n = 93) and anchovy (Engraulis encrasicolus) (n = 69), caught in the North-Eastern Atlantic, West Mediterranean and Adriatic Sea. The larvae found in the dissected fish were identified in the following order of abundance: A. simplex (s.l.) (n = 2003), Hysterothylacium aduncum (n = 422), H. fabri (n = 180) and A. physeteris (n = 15). Binomial regression analysis showed a correlation between A. simplex (s.l.) and Hysterothylacium larvae abundance and the host geographical location, the North-Eastern Atlantic being the area with the highest parasitation. Fish length and weight and Fulton's condition factor were correlated with A. simplex (s.l.) abundance only in horse mackerel. There was a significant presence of A. simplex (s.l.) and H. aduncum larvae in the musculature of North-Eastern Atlantic blue whiting, the most parasitized part being the anteroventral region, followed equally by the anterodorsal and central sections. The ITS rDNA of larvae of the sibling species A. simplex (s.s.) and A. pegreffii was identified by PCR-RFLP, and a binary logistic regression model was developed to study their morphometric differentiation. Anisakis simplex (s.s.) was detected in the North-Eastern Atlantic and A. pegreffii in all the areas studied. The morphometric analysis discriminated between the two species at the third and fourth larval stages (L3 and L4), the latter obtained by in vitro culture in RPMI-1640 medium. Two discriminant functions were obtained for the L3 and L4 larvae, the ventricle being a key parameter for specific differentiation in both stages, providing taxonomical criteria that could be used besides molecular identification. The present study reveals differences in the parasitation of the studied fish, including the distribution of larvae in the musculature, related to the host species and its geographical origin.

Anisákidos y anisakidosis: generalidades y su actualidad en Colombia. Revisión bibliográfica

La anisakidosis es una parasitosis ocasionada por nematodos de la familia Anisakidae, causadapor el consumo de pescado parasitado con larvas infectivas (L3) de estos nematodos. EnEuropa y Asia es un problema de salud pública. Sin embargo, en Colombia y en general enlos países de América del Sur, es poco conocida. El objetivo de este trabajo es presentar unarevisión de las generalidades de los parásitos anisákidos y mostrar la situación actual de estaparasitosis en Colombia. Se realizó una búsqueda estructurada de términos MeSH y DeCS enMEDLINE, Cochrane, Embase, LILACS y Scopus; esta se complementó con otra no estructurada en SciELO y Google Scholar. Se incluye un reporte de caso y seis registros de hospederos. Se describen registros de peces de consumo humano parasitados por Anisakis sp., Anisakis physeteris y Pseudoterranova decipiens para el Océano Pacífico y, los géneros Pseudoterranova y Contracaecum en peces del Océano Atlántico y aguas continentales. Se concluye que la anisakidosis representa un riesgo latente para Colombia, es necesario instaurar legislaciones efectivas para un control eficiente sobre esta parasitosis y educar a la población sobre los cuidados necesarios para el consumo de pescado.

A Perspective Around Cephalopods and Their Parasites, and Suggestions on How to Increase Knowledge in the Field

Although interest in several areas of cephalopod research has emerged over the last decades (e.g., neurobiology, aquaculture, genetics, and welfare), especially following their 2010 inclusion in the EU Directive on the use of animals for experimental purposes, knowledge regarding the parasites of cephalopods is lacking. Cephalopods can be intermediate, paratenic, or definitive hosts to a range of parasites with a wide variety of life cycle strategies. Here, we briefly review the current knowledge in cephalopod parasitological research, summarizing the main parasite groups that affect these animals. We also emphasize some topics that, in our view, should be addressed in future research, including: (i) better understanding of life cycles and transmission pathways of common cephalopod parasites; (ii) improve knowledge of all phases of the life cycle (i.e., paralarvae, juveniles, adults and senescent animals) and on species from polar deep sea regions; (iii) exploration of the potential of using cephalopod-parasite specificity to assess population boundaries of both, hosts and parasites; (iv) risk evaluation of the potential of standard aquacultural practices to result in parasite outbreaks; (v) evaluation and description of the physiological and behavioral effects of parasites on their cephalopod hosts; (vi) standardization of the methods for accurate parasite sampling and identification; (vii) implementation of the latest molecular methods to facilitate and enable research in above mentioned areas; (viii) sharing of information and samples among researchers and aquaculturists. In our view, addressing these topics would allow us to better understand complex host-parasite interactions, yield insights into cephalopod life history, and help improve the rearing and welfare of these animals in captivity.

Influence of confluent marine currents in an ecotonal region of the South-West Atlantic on the distribution of larval anisakids (Nematoda: Anisakidae)

Background

In the marine environment, transitional zones between major water masses harbour high biodiversity, mostly due to their productivity and by containing representatives of species characteristic of adjacent communities. With the aim of assessing the value of larval Anisakis as zoogeographical indicators in a transitional zone between subtropical and sub-Antarctic marine currents, larvae obtained from Zenopsis conchifer were genetically identified. Larvae from Pagrus pagrus and Merluccius hubbsi from two adjacent zoogeographical provinces were also sequenced.

Results

Four species were genetically identified in the whole sample, including Anisakis typica, A. pegreffii, A. berlandi and a probably new species related to A. paggiae. Anisakis typica and A. pegreffii were identified as indicators of tropical/subtropical and sub-Antarctic waters, respectively, and their presence evidenced the transitional conditions of the region. Multivariate analyses on prevalence and mean abundance of Anisakis spp. of 18 samples represented by 9 fish species caught south of 35°S determined that host trophic level and locality of capture were the main drivers of the distribution of parasites across zoogeographical units in the South-West Atlantic.

Conclusions

Most samples followed a clear zoogeographical pattern, but the sample of Z. conchifer, composed mostly of A. typica, was an exception. This finding suggests that population parameters of A. typica and A. pegreffii could differ enough to be considered as a surrogates of the identity of larvae parasitizing a given host population and, therefore, a step forward the validation of the use of larval Anisakis as biological indicators for studies on host zoogeography.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3119-7) contains supplementary material, which is available to authorized users.

Occurrence of Anisakis and Hysterothylacium larvae in commercial fish from Balearic Sea (Western Mediterranean Sea)

This study investigates the occurrence of anisakids and raphidascarids in commercial fish from Balearic Sea (Western Mediterranean). A total of 335 fish including 19 black anglerfish (Lophius budegassa), 33 white anglerfish (L. piscatorius), 129 European hake (Merluccius merluccius), 30 red mullet (Mullus barbatus), and 124 striped mullet (M. surmuletus) were examined using enzymatic digestion. A total of 948 nematode larvae were isolated (prevalence 52.53%) being the highest prevalence observed in striped mullet. Forty-six larvae were identified using molecular analyses which included PCR and sequencing of the 629-bp fragment of mitochondrial cox2 gene region. Anisakis pegreffii (80.43%), A. physeteris (8.69%), Hysterothylacium fabri (6.52%), and A. simplex (4.35%) were detected based on molecular analyses of larvae. Total nematode prevalence was positively correlated with weight, length, condition factor, and maturity stage of the host and also with fishing ground depth. Statistical differences between total nematode prevalence and geographical sector of capture were observed when fishing hauls were grouped according to the abundance of sperm whales or common bottlenose dolphins. The results also corroborate that fishing water depth may play an important role in anisakid and raphidascarid parasitization.

Molecular Epidemiology of Anisakis and Anisakiasis: An Ecological and Evolutionary Road Map

This review addresses the biodiversity, biology, distribution, ecology, epidemiology, and consumer health significance of the so far known species of Anisakis, both in their natural hosts and in human accidental host populations, worldwide. These key aspects of the Anisakis species' biology are highlighted, since we consider them as main driving forces behind which most of the research in this field has been carried out over the past decade. From a public health perspective, the human disease caused by Anisakis species (anisakiasis) appears to be considerably underreported and underestimated in many countries or regions around the globe. Indeed, when considering the importance of marine fish species as part of the everyday diet in many coastal communities around the globe, there still exist significant knowledge gaps as to local epidemiological and ecological drivers of the transmission of Anisakis spp. to humans. We further identify some key knowledge gaps related to Anisakis species epidemiology in both natural and accidental hosts, to be filled in light of new 'omic' technologies yet to be fully developed. Moreover, we suggest that future Anisakis research takes a 'holistic' approach by integrating genetic, ecological, immunobiological, and environmental factors, thus allowing proper assessment of the epidemiology of Anisakis spp. in their natural hosts, in human populations, and in the marine ecosystem, in both space and time.

No more time to stay 'single' in the detection of Anisakis pegreffii, A. simplex (s. s.) and hybridization events between them: a multi-marker nuclear genotyping approach

A multi-marker nuclear genotyping approach was performed on larval and adult specimens of Anisakis spp. (N = 689) collected from fish and cetaceans in allopatric and sympatric areas of the two species Anisakis pegreffii and Anisakis simplex (s. s.), in order to: (1) identify specimens belonging to the parental taxa by using nuclear markers (allozymes loci) and sequence analysis of a new diagnostic nuclear DNA locus (i.e. partial sequence of the EF1 α-1 nDNA region) and (2) recognize hybrid categories. According to the Bayesian clustering algorithms, based on those markers, most of the individuals (N = 678) were identified as the parental species [i.e. A. pegreffii or A. simplex (s. s.)], whereas a smaller portion (N = 11) were recognized as F1 hybrids. Discordant results were obtained when using the polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLPs) of the internal transcribed spacer (ITS) ribosomal DNA (rDNA) on the same specimens, which indicated the occurrence of a large number of 'hybrids' both in sympatry and allopatry. These findings raise the question of possible misidentification of specimens belonging to the two parental Anisakis and their hybrid categories derived from the application of that single marker (i.e. PCR-RFLPs analysis of the ITS of rDNA). Finally, Bayesian clustering, using allozymes and EF1 α-1 nDNA markers, has demonstrated that hybridization between A. pegreffii and A. simplex (s. s.) is a contemporary phenomenon in sympatric areas, while no introgressive hybridization takes place between the two species.

Parasites as Biological Tags for Stock Discrimination of Beaked Redfish (Sebastes mentella): Parasite Infra-Communities vs. Limited Resolution of Cytochrome Markers

The use of parasites as biological tags for discrimination of fish stocks has become a commonly used approach in fisheries management. Metazoan parasite community analysis and anisakid nematode population genetics based on a mitochondrial cytochrome marker were applied in order to assess the usefulness of the two parasitological methods for stock discrimination of beaked redfish Sebastes mentella of three fishing grounds in the North East Atlantic. Multivariate, model-based approaches demonstrated that the metazoan parasite fauna of beaked redfish from East Greenland differed from Tampen, northern North Sea, and Bear Island, Barents Sea. A joint model (latent variable model) was used to estimate the effects of covariates on parasite species and identified four parasite species as main source of differences among fishing grounds; namely Chondracanthus nodosus, Anisakis simplex s.s., Hysterothylacium aduncum, and Bothriocephalus scorpii. Due to its high abundance and differences between fishing grounds, Anisakis simplex s.s. was considered as a major biological tag for host stock differentiation. Whilst the sole examination of Anisakis simplex s.s. on a population genetic level is only of limited use, anisakid nematodes (in particular, A. simplex s.s.) can serve as biological tags on a parasite community level. This study confirmed the use of multivariate analyses as a tool to evaluate parasite infra-communities and to identify parasite species that might serve as biological tags. The present study suggests that S. mentella in the northern North Sea and Barents Sea is not sub-structured.