The European hake, one of the most commercially valuable species in ICES fishing areas, is considered an important neglected source of zoonotic risk by nematode parasites belonging to the genus Anisakis. Merluccius merluccius is, by far, the most important host of Anisakis spp. at the European fishing grounds, in terms of demographic infection values, and carries the highest parasite burden. These high parasite population densities within an individual fish host offer a chance to explore new sources of variations for the genetic structure of Anisakis spp. populations. A total of 873 Anisakis spp. third-stage larvae, originally sampled from viscera and muscular sections of hake collected at ten fishing grounds, were primarily identified using ITS rDNA region as molecular marker. After that, we used mtDNA cox2 gene to reveal the high haplotype diversity and the lack of genetic structure for A. simplex. Dominant haplotypes were shared among the different fishing areas and fish sections analyzed. Results indicate a clear connection of A. simplex from European hake along the Northern North Sea to the Portuguese coast, constituting a single genetic population but revealing a certain level of genetic sub-structuring on the Northwest coast of Scotland. This study also provides useful information to advance the understanding of parasite speciation to different fish host tissues or microenvironments.

A tropicalization phenomenon of ichthyofauna has been described in the last decades in Galicia (north‐eastern Atlantic), with increasing reports of tropical and subtropical fishes appearing northward this distribution range. A search for parasites was carried out in the digestive tract of two specimens first captured in Galician waters: the prickly pufferEphippion guttifer(Tetraodontidae) and the African stripped gruntParapristipoma octolineatum(Haemulidae). Examination ofE. guttifershowed high intensity of nematodes, from three different genera:Cucullanus(Cucullanidae),Hysterothylacium(Raphidascaridae) andAnisakis(Anisakidae), with demonstrated pathogenicity to humans. Molecular identification allowed the identification ofAnisakis pegreffii, already described in the area, and first reports for European waters ofCucullanus dodsworthi,Hysterothylacium reliquensand a newHysterothylaciumsp. P. octolineatumshowed a far lower level of parasitization, with twoHysterothylaciumlarvae, genetically identified asHysterothylacium deardorffoverstreetorum, also its first report in the eastern Atlantic. Thus, possible ecological impact of the occurrence of two non‐native individual fishes in a new area could be remarkably higher if we see this issue through the lens of the parasitological perspective, as far as only two individual fish can harbour more of one hundred nematode parasites belonging to different species, most of them also new species for that area.

In the last 25 years, nematode parasites of the genus Anisakis have attracted international attention from various socio-economic sectors, with serious concern about the impact of these parasites on seafood quality and safety, and public health (related to both zoonoses and allergy). A knowledge-based understanding of the population structure of Anisakis spp. is useful to provide valuable data about the infection dynamics, host specificity and its ability to adapt to local environments and to climate change by adapting to the food-web structure. This study first aimed to investigate the taxonomic biodiversity of Anisakis spp. collected from commercial fish and cetacean species from the most significant Northeast Atlantic fishing grounds and evaluate the ecological connections of A. simplex and A. pegreffii (L3 and adults) in cetaceans and fish from NW Spain, through the analysis of their genetic diversity and population structure. A total of 1399 Anisakis spp. L3 larvae from six fish species and 475 adults from six cetacean species were identified using the ITS rDNA region as a molecular marker. Molecular identification allowed for the first detection of A. berlandi in European waters parasitizing the long-finned pilot whales Globicephala melas and the first report of A. nascettii and A. zhiphidarum infecting the striped dolphin Stenella coeruleoalba, as well as the identification of A. simplex, A. pegreffii and the hybrid genotype between both species. The analysis of the mitochondrial cytochrome oxidase 2 gene of A. simplex and A. pegreffii, the most prevalent species in FAO area 27, revealed panmictic populations for both species with high haplotype diversity. The predatory–prey relationship involving two major fish species (European hake and blue whiting) and the common dolphin appears to provide an important mechanism for maintaining genetic diversity and structure in major Anisakis species in the NE Atlantic.

Urastoma cyprinae is a turbellarian parasite infecting the gills of several marine bivalves. We observed the presence of virus-like particles (24 to 30 nm in diameter; icosahedral symmetry) arranged in paracrystalline arrays in the cytoplasm of subepidermal dorsal cells. These particles appear to be RNA viruses, possibly related to the Picornaviridae. This is the first report of viral particles in the parasite U. cyprinae.