Derogenes Varicus Research Articles

Reconstruction of Derogenes varicus Miracidium (Digenea: Derogenidae): First Ultrastructural Description of Spines on the Surface of Hemiurata Larvae.

We performed a detailed ultrastructural reconstruction of the "passive" miracidium of Derogenes varicus Muller, 1784 , a species from the Hemiurata group. The miracidium is highly miniaturized and simplified in comparison with the "active" miracidia. For the first time we elucidated the nature of the spines on the surface of the hemiuroid larva: they are derivatives of the epithelial plates. The anterior end of the larva is equipped with three epithelial plates that bear both spines and cilia. The major part of the miracidial surface is formed by the tegument. The nervous and excretory systems of the D. varicus miracidium are extremely reduced. Single undifferentiated cell comprises the germinal material of the miracidium. We discuss the trends of evolution of hemiuroid miracidia that are associated with the transition to passive strategy of infection.

Comparative analysis of the cytoarchitecture of the excretory bladder of adult Digenea (Platyhelminthes) with consideration of the presence of mineralized excretory corpuscles in marine and freshwater adult worms

The ultrastructural differences are shown between the cytoarchitecture of the excretory bladder and excretory inclusions in four digenean species, two azygiids, the marine Otodistomum cestoides and the freshwater Azygia lucii, the marine derogenid Derogenes varicus and the freshwater allocreadiid Acrolichanus auriculatus. The unusual cytoarchitecture of the bladder epithelium of the azygiid digeneans, consisting along its entire length of two alternating, morphologically different zones, tegumental and cellular excretory epithelial zones, connected by septate junctions, has recorded for the first time for the Digenea and, in general, for the Neodermata. It, possible, suggests the participation of the tegumental distal cytoplasmic layer in the formation of their excretory bladder epithelium. Like most digeneans, the excretory bladder of A. auriculatus and D. varicus has a syncytial epithelial lining. Based on available literature and our own results, we can confirm the presence of the excretory corpuscles in adult marine digeneans and their absence from freshwater species, regardless of the digenean localization in their host. The present study shown that in marine digeneans, the excretory corpuscles are associated with specialized excretory cells or excretory syncytial epithelium. Ultrastructural data were obtained on the possible growth of the excretory bladder epithelium due to the migration of undifferentiated cells into the epithelial lining in studied marine species. We may assume that the bladder epithelium of marine adult digeneans specializes, in addition to the excretory function, in osmoregulatory function.

Untangling the Derogenes varicus species complex in Scandinavian waters and the Arctic: description of Derogenes abba n. sp. (Trematoda, Derogenidae) from Hippoglossoides platessoides and new host records for D. varicus (Müller, 1784) sensu stricto.

Several studies have shown that the euryxenic trematode Derogenes varicus (Müller, 1784) represents a species complex. Four lineages have been designated (DV1-4) with the DV1 clade corresponding to D. varicus sensu stricto. Herein, we investigate newly collected specimens of D. varicus sensu lato from Scandinavian and Arctic waters using integrative taxonomy. The trematodes were collected from Melanogrammus aeglefinus, Eutrigla gurnardus, Trachinus draco, and Merluccius merluccius off the Atlantic coast of Sweden and from Hippoglossoides platessoides from Arctic Svalbard. 28S sequences of derogenids from Sweden were identical to D. varicus sensu stricto, confirming its euryxeny. The 28S sequences of Derogenes sp. from H. platessoides were identical to Derogenes DV2 and differed from D. varicus sensu stricto by 3% and from Derogenes DV3 by 2%. The 28S sequence divergences of Derogenes sp. from H. platessoides with D. ruber and D. lacustris were 3 and 10%, respectively. ITS2 and cox1 divergences between Derogenes sp. from H. platessoides and other Derogenes species/lineages were at levels of interspecific differences. The species from H. platessoides is described here as D. abba n. sp. We also examined the type material of Progonus muelleri (Levinsen, 1881), the type and only species of the genus Progonus, with redescription and designations of paralectotypes. Based on specimens from Theodor Odhner's collections at the Swedish Museum of Natural History, SMNH, Stockholm, we provide novel morphological and anatomical data for D. varicus sensu lato species complex. Lastly, we investigated Arthur Looss's "lost collection" of Trematodes at the SMNH and characterised a putative species Derogenes sp. "limula".

The helminthofauna of the pink salmon <i>Oncorhynchus gorbuscha</i> (Walbaum, 1792) of south-east Sakhalin according to the results of many years of research

The purpose of the research is to describe and analyze the qualitative and quantitative composition of pink salmon helminths of southeastern Sakhalin.Materials and methods. Standard parasitological methods of collecting material were used. At the autopsy, the ureters, eyeballs, gill petals and arches, and the brain of fish were not examined. The method of collecting salmon parasites in the laboratory has been unchanged since 1992. Collections of representatives of monogenetic suckers were not carried out. Parasitological studies of pink salmon of southeastern Sakhalin were carried out from 1992 to 2022, a total of 4163 fish specimens were examined. The fish is caught in the estuaries of rivers and the sea coast.Results and discussion. According to the results of their own research and literature data, the pink salmon helminth fauna of southeastern Sakhalin is represented by 23 species: Dibothriocephalus nihonkaiensis pl., Eubothrium salvelini, Eu. crassum, Nybelinia surmenicola pl., Pelichnibothrium speciosum pl., Tetraphyllidea gen. sp., Brachyphallus crenatus, Cryptocotyle sp. mtc., Hemiurus levinseni, Lecithaster gibbosus, Prosorhynchoides gracilescens, Parahemiurus merus, Derogenes varicus, Capiatestes thyrsitae, Corynosoma strumosum l., Echinorhynchus gadi, Bolbosoma caenoforme juv., B. bobrovoi juv., Rhadinorhynchus trachuri, Anisakis simplex l., Ascarophis pacifica, Ascarophis skrjabini, Hysterothylacium aduncum. The qualitative composition of the helminth fauna is currently undergoing minor changes, while the quantitative characteristics of some helminths are significantly reduced. Thus, the infection of pink salmon with Bolbosoma sp. juv scrapers. decreased to 0.61±0.18.

Reconstruction of Derogenes varicus miracidium (Digenea: Derogenidae): first ultrastructural description of spines on the surface of Hemiurata larvae

We performed the detailed ultrastructural reconstruction of the “passive” miracidium of Derogenes varicus - the species from Hemiurata group. The miracidium is highly miniaturized and simplified in comparison with the “active” miracidia. For the first time we elucidate the nature of the spines on the surface of hemiuroid larva: they are derivatives of the epithelial plates. The anterior end of the larva is equipped with three epithelial plates, that bear both spines and cilia. The major part of the miracidial surface is formed by tegument. The nervous and excretory systems of the D. vari cus miracidium are extremely reduced. Single undifferentiated cell comprises the germinal material of the miracidium. We discuss the trends of evolution of hemiuroid miracidia that are associated with transition to passive strategy of infection.

Hidden in the fog: morphological and molecular characterisation of Derogenes varicus sensu stricto (Trematoda, Derogenidae) from Sweden and Norway, and redescription of two poorly known Derogenes species.

Derogenes varicus (Müller, 1784) is widely reported as a trematode with exceptionally low host specificity and a wide, bipolar distribution. However, several recent studies have suggested that D. varicus represents a species complex and based on molecular evidence, four genetic lineages (labeled as "DV1-4") have been designated within the D. varicus species complex. This possibility requires improved (ideally molecular) characterisation of specimens from the type-host (Salmo salar) and type-locality (off Denmark). During examination of trematode parasites of fish from Scandinavian and Arctic waters (Sweden and Norway), we found specimens of D. varicus in the stomach of Merlangius merlangus off the coast of Sweden, and in Gadus morhua off the coast of Sweden and Norway; we compared them to D. varicus from the type-host, the Atlantic salmon Salmo salar fromNorway, to verify their conspecificity. Newly generated sequences (28S rDNA, ITS2 and cox1) of Scandinavian and Arctic specimens consistent with D. varicus all formed a single clade, DV1. 28S sequences of D. varicus from S. salar from Norway, i.e., close to the Danish type locality, clustered within the DV1 clade along with sequences of D. varicus from various hosts including Limanda limanda, G. morhua and Myoxocephalus scorpius from the White Sea and the Barents Sea (Russia), without any host-related structuring. We thus consider that the lineage DV1 represents D. varicus sensu stricto. Additionally, specimens from M. merlangus had a similar morphology and anatomy to those of D. varicus from L. limanda, G. morhua and M. scorpius from T. Odhner's collection, supporting the presence of a single species in the DV1 lineage designated herein as D. varicus sensu stricto. We redescribe D. varicus sensu stricto, add new morphological characters and provide morphometric data. We infer that D. varicus types DV2-4 all relate to separate species. We also revise type-specimens of Derogenes minor Looss, 1901 from the A. Looss collection in the Swedish Museum of Natural History and provide redescriptions of it and of the type-species of the genus, Derogenes ruber Lühe, 1900. In light of their morphological distinctiveness relative to D. varicus sensu stricto, we reinstate D. parvus Szidat, 1950 and D. fuhrmanni Mola, 1912.

Species complexes and life cycles of digenetic trematodes from the family Derogenidae.

The best way to study digenean diversity combines molecular genetic methods, life-cycle studies and elaborate morphological descriptions. This approach has been barely used for one of the most widespread digenean taxa parasitizing fish – the superfamily Hemiuroidea. Here, we applied the integrative approach to the hemiuroideans from the family Derogenidae parasitizing fish at the White and Barents Seas. Analysis of 28S, 18S, 5.8S rDNA, ITS2 and cox1 gene sequences from sexually adult worms (maritae) showed genetic heterogeneity for 2 derogenid species known from this area: Derogenes varicus and Progonus muelleri. Thus, 2 pairs of genetic lineages were found: DV1 and DV2, PM1 and PM2, respectively. Data from other regions indicate that 2 more lineages of D. varicus probably exist. Based on previous records from the White and Barents Seas, we hypothesized that the cercariae found in the moonsnails (family Naticidae) belong to the Derogenidae and may help to differentiate these lineages as species. According to our results, Cercaria appendiculata from Cryptonatica affinis matched DV1, similar nameless cercariae from Euspira pallida and Amauropsis islandica matched DV2, and Cercaria octocauda from C. affinis matched PM1. We provide new data on the structure of these cercariae and discuss the life-cycle pattern of the studied digeneans.

First record of Derogenes varicus and Dinurus scombri (Digenea: Hemiurata) from Red Sea fishes, Yemen

Two widely distributed and economically important food fish in the Red Sea were investigated. A total of 101 specimens of Epinephelus tauvina and 120 Abalistes stellatus were collected from Al-Mehwat local fish market, Hodeidah City, Yemen, between October 2009 and April 2010 and examined for their parasites. Two digenean species of the suborder Hemiurata, namely Derogenes varicus (Müller, 1784) and Dinurus scombri Yamaguti, 1934, were found in these fishes. The former parasite occurred in 15% of A. stellatus and 4% of E. tauvina and its mean intensity of infection was 4.2 and 3.5, respectively while the abundance was 15 and 4, respectively. The latter parasite occurred only in 1% of E. tauvina, with a mean intensity of 2 and an abundance of 0.02. The present study represents the first record of these two parasite species in Yemeni waters of the Red Sea. In addition, E. tauvina now represents a new host for D. scombri.

Phylogenetic position of the hemiuroid genus Paraccacladium Bray & Gibson, 1977 (Trematoda: Hemiuroidea) and the status of the subfamily Paraccacladiinae Bray & Gibson, 1977

ABSTRACT In this study we tested the current taxonomic model of the trematode superfamily Hemiuroidea, according to which the genus Paraccacladium belongs to the family Accacoeliidae. We reconstructed the phylogeny of the hemiuroid Clade A using novel 28S rRNA gene sequences of Paraccacladium sp., Derogenes varicus, Progonus muelleri and Lampritrema miescheri as well as data available in GenBank. Based on phylogenetic data, the genus Paraccacladium should be assigned to a separate family, the Paraccacladiidae Bray & Gibson, 1977 stat. nov. The morphological differences between the Paraccacladiidae and the Accacoeliidae are the absence of a uroproct, anteriorly directed diverticula of intestinal caeca, and the position of Mehlis’ gland, posterior or postero-lateral to the ovary. Phylogenetic analysis indicates a sister relationship between the Derogenidae and the Sclerodistomidae. It also shows that the Paraccacladiidae, on the one hand, and a group of families, the Accacoeliidae, Hirudinellidae and Syncoeliidae, on the other, share the most recent common ancestor. Our data support the hypothesis that the genus Lampritrema is affiliated to the Hirudinellidae. Genetic divergence between North Atlantic and North Pacific isolates of D. varicus was also determined.

Phylogenetic position of the genus Gonocerca Manter, 1925 (Trematoda, Hemiuroidea), based on partial sequences of 28S rRNA gene and a reconsideration of taxonomic status of Gonocercinae Skrjabin et Guschanskaja, 1955

Adult trematodes of the genus Gonocerca Manter, 1925, are parasites of marine fishes. Identification of the phylogenetic positions and a revision of the taxonomic status of the subfamily Gonocercinae Skrjabin et Guschanskaja, 1955 (Derogenidae) are the main purposes of this research article. Four Gonocerca species were used in the study, including the type-species G. phycidis Manter, 1925. Molecular phylogenetic analysis, based on partial sequences of 28S rRNA gene, revealed that Gonocerca spp. are phylogenetically distant from other hemiuroid trematodes, including Derogenes varicus (Müller, 1784), representative of the type-genus of the family Derogenidae. The taxonomic rank of Gonocercinae should be raised to the family level. The generic composition of the family Gonocercidae Skrjabin et Guschanskaja, 1955 stat. nov., requires further clarification as the molecular data do not support the inclusion of the genus Hemipera Nicoll, 1913, in this family.

Parasitation of sea trout (Salmo trutta trutta L.) from the spawning ground and German coastal waters off Mecklenburg-Western Pomerania, Baltic Sea.

A total of 52 sea trouts, Salmo trutta trutta, were studied for parasites, originating from German freshwater streams and coastal waters of the Baltic Sea. While 35 specimens were caught mainly close to the shoreline in the Baltic Sea, 17 were sampled during their spawning migration in Warnow River and other neighboring rivers in Mecklenburg-Western Pomerania. A total of 12 different metazoan parasite species were found in sea trout originating from the Baltic Sea, including five digeneans, two cestodes, three nematodes, and two acanthocephalans. Marine and freshwater species were found. In the migratory trout, seven different parasite species were recorded (one digenean, two cestodes, one nematode, and one acanthocephalan), demonstrating lower parasite diversity and load during the spawning migration compared with the fish from the Baltic Sea. The anisakid nematodes Anisakis simplex (sensu stricto), Contraceacum rudolphii, and Hysterothylacium aduncum were identified by molecular analyses of the ITS-1, 5.8S, ITS-2, and flanking sequences of the rDNA. Together with the digenean Derogenes varicus, Hemiurus communis and H. luehei, and the cestode Diphyllobothrium dendriticum seven new host records for sea trout from the German part of the Baltic Sea are made.

Digenea in notothenioid fish in the Beagle Channel (Magellanic sub-region, sub-Antarctica)

Fish of five species of Notothenioidei (104 specimens), Cottoperca trigloides, Patagonotothen brevicauda, P. longipes, P. tessellata and Champsocephalus esox, caught in the Beagle Channel (Magellanic sub-region, sub-Antarctica) were infected with Digenea of nine species (1130 specimens). Faunistic data on the occurrence of all nine parasites are provided. The most abundant digenean species was Macvicaria magellanica found in the intestine of three host species of the genus Patagonotothen. The second most abundant digenean species was Elytrophalloides oatesi found in the stomach of four host species, with exception of P. brevicauda. Three digenean species: Stenakron kerguelense, Whitegonimus ozoufae and Genolinea bowersi, were more abundant in fish caught at the harbor of Ushuaia (depth 7-9 m), remaining six species: M. magellanica, Neolepidapedoides subantarcticus, Postmonorchis variabilis, Derogenes varicus, E. oatesi and Lecithaster macrocotyle, in the eastern mouth of the Beagle Channel (depth 30 m).

Annual and spatial variability in endo- and ectoparasite infections of North Sea cod (Gadus morhua Linnaeus, 1758) larvae, post-larvae and juveniles.

A parasitological investigation was performed on a total of 5380 Atlantic cod larvae, post-larvae and small juveniles sampled from the North Sea during a period of five years. The copepod Caligus elongatus (Von Nordmann, 1832) and the nematode Hysterothylacium aduncum (Rudolphi, 1802) were found at a relatively high prevalence of infection (4.6% and 5.2%, respectively). The infection by both parasites showed annual and spatial variability. C. elongatus showed a higher prevalence in 1992 compared to the following years, whereas the prevalence of H. aduncum increased from 1992 to 2001.We observed a relation between parasite distribution and parameters such as latitude and water depth. Adult digeneans (Lecithaster gibbosus and Derogenes varicus) and larval cestodes were also found with lower infection rates. Since changes of infection levels coincided with increasing North Sea water temperature in the studied period, it is hypothesized that temperature may affect parasite population levels. However, it is likely that other environmental factors may contribute to the observed variations. Absence of infection intensities higher than one nematode per fish in small larvae and post-larvae suggests that host survival may be affected by a high infection pressure. The relatively high levels of infection in the younger stages of cod, and the annual/spatial variability of these infections should be considered in the understanding of the early life dynamics of the species.

Boreogadus saida (Lepechin) (Gadidae): a review of its metazoan parasite fauna from Greenland, eastern Canada, Alaska and the Russian Arctic

The metazoan parasite fauna of 50 specimens of Boreogadus saida (Lepechin) (Gadidae) from eastern Greenland is very similar to those of previous studies of the parasite fauna of B. saida from Greenland, eastern Canada, Alaska and the Russian Arctic. The digeneans Hemiurus levinseni, Derogenes varicus and Lecithaster gibbosus and cestode larvae were found at most stations. Single specimens of the nematode larvae Anisakis simplex were found at four stations. A comparison of the distribution of the larvae of Contracaecum sp. and Hysterothylacium sp. is difficult due to a possible confusion of the two genera. Most of the metazoan parasites of B. saida are generalist species found in several fish families. Boreogadus saida acquires most of its endoparasites by eating pelagic crustaceans, mainly copepods and amphipods. It plays an important role in the arctic ecosystem and its parasites are transferred to predatory fish, birds and mammals through the food web.

Metazoan parasites of the stomach of Dissostichus eleginoides Smitt 1898 (Pisces: Notothenidae) from southern Chile: A tool for stock discrimination?

The taxonomic composition of the metazoan parasites found in the stomach of 629 specimens of the “Patagonian toothfish” Dissostichus eleginoides Smitt, 1898, from two localities in southern Chile (Lebu 36°00′S; Quellón 48°49′S), is recorded. More than 58,000 parasite specimens belonging to 9 taxa were registered. Adult worms were represented by the hemiurids Gonocerca phycidis Manter 1925, Lecithochirium genypteri Luhe 1905, Brachyphallus crenatus (Rudolphi 1802), and Derogenes varicus (Muller 1784) and the nematode Hysterothylacium sp. Ward & Magath 1917. Larval forms of anisakid nematodes, an acanthocephalan ( Corynosoma sp.), a trypanorhynch cestode ( Hepatoxylon trichiuri (Holten 1802)) and an unidentified pseudophyllidean cestode were also obtained. Parasitological evidence, based on univariate and multivariate analys is, does not support either the existence of discrete stocks, migratory movements between areas or seasonality in pattern of infection.

Parasite communities of eels Anguilla anguilla in freshwater and marine habitats in Iceland in comparison with other parasite communities of eels in Europe

Ninety-five eels from one marine and three freshwater localities in Iceland were examined for parasites. Twenty species were found, 12 from marine habitat, 12 from freshwater and 4 species were found in both habitats. These are: Eimeria anguillae, Chilodonella hexasticha, Trichodina fultoni, T. jadranica, Myxidium giardi, Myxobolus kotlani, two Zschokkella spp., Derogenes varicus, Deropristis inflata, Diplostonmum sp., Plagioporus angulatus, Podocotyle atomon, Anisakis simplex (larva), Eustrongylides sp. (larva), Hysterothylacium aduncum (larva), Raphidascaris acus (larval and adult stages), Bothriocephalus claviceps, Proteocephalus macrocephalus, and a pseudophyllidean larva. Thirteen of these species are new parasite records from Icelandic waters. The component community of marine eels was characterized by low diversity and a high dominance of a single species. Overall, seven species of helminths were observed, up to five different species occurring in an individual fish. The component community of the freshwater eels was species-poor with low diversity and relatively high dominance of single species. A between-sites difference in the freshwater eels was considerable; only Diplositonun sp. was found at more then one sampling site. Similar to previous studies, there is a total replacement of freshwater macroparasite species by marine ones in saline waters. But unlike research abroad in which species richness decreases with higher salinity, the marine eels in Iceland have considerably higher richness than the freshwater ones. The parasite communities of freshwater eels in Iceland are, in general species-poorer, less diverse and having higher Berger Parker (BP) dominance than other eel communities in Europe. Marine eels have on the other hand comparable species richness, are less diverse and with a high BP dominance.

Influence of climatic changes on the parasites of Atlantic cod Gadus morhua off coastal Labrador, Canada

A study was conducted in 2000 and 2003, following the collapse of the commercial fishery in 1990, to compare metazoan parasites of Atlantic cod Gadus morhua, captured off coastal Labrador, with samples taken in 1980 and 1986. Fish were captured by otter trawl offshore in the North Atlantic Fish Organisation subarea 2J. Parasites were removed from the digestive tract, stained, identified and compared between the different groups. Both the prevalence and mean abundance of trematodes, larval nematodes and E. gadi were significantly lower in fish taken in 2000 and 2003 than in 1980. While mean values of trematodes and nematodes declined in 1986, those of Echinorhynchus gadi remained unchanged in 1986 and 1990. Four-year-old cod sampled in 1990 harboured significantly fewer E. gadi than older age groups. The most commonly occurring trematodes included Podocotyle reflexa, Lepidapedon elongatum, Derogenes varicus and Hemiurus levinseni while the larval nematode, Anisakis sp. was predominant. Comparison of offshore samples taken in 2000 and 2003 with others taken in previous years suggests an overall decline of parasites coincident with a change in climatic conditions, the absence of a major food source, namely capelin Mallotus villosus, of cod and ultimately the decline of the Labrador population.

Digeneans from deep-sea marine teleosts off the Outer Hebrides, Scotland, including the description of Brachyenteron helicoleni sp. nov. (Zoogonidae)

AbstractFifteen species of digeneans are reported from the waters off the islands of the Outer Hebrides, off north-western Scotland. Trifoliovarium allocytti comb. nov. from Neocyttus helgae is described, figured, and reported for the first time in the northern hemisphere. Brachyenteron helicoleni sp. nov. from Helicolenus dactylopterus is described and considered distinct from other species in the genital pore being at the level of the pharynx, the relatively narrow caeca, the vitellarium being mainly at the level of the ventral sucker and the anterior hindbody, the posteriorly situated, oblique testes, the small amount of post-testicular uterus, the small, delicate cirrus-sac and the large eggs. Derogenes varicus and Lepidapedon arlenae are reported from Caelorhinchus labiatus and Paralepidapedon williamsi is reported from Cottunculus thomsoni for the first time. Steringovermes notacanthi and Prodistomum priedei are reported from off Scotland for the first time. The reports of Derogenes varicus at 1,800 m depth and Zoogonoides viviparus at 1,000 m are deeper records than have previously been published.

Use of parasite and genetic markers in delineating populations of winter flounder from the central and south‐west Scotian Shelf and north‐east Gulf of Maine

Discriminant function analyses of infection parameters of parasitic helminths revealed that abundances of seven helminth species contributed significantly to the delineation of four host populations of winter flounder Pleuronectes americanus from the central and south‐west Scotian Shelf and the north‐east Gulf of Maine (NAFO subdivision 4WX‐5Z). These were adult digeneans, Derogenes varicus, Genolinea laticauda, Steganoderma formosum and Steringophorus furciger, metacercariae of the digenean, Stephanostomum baccatum, and larval nematodes, Anisakis simplex and Hysterothylacium aduncum. The correct classification rate was 84% overall, with Georges Bank (5Z) and Sable Island Bank (4W) winter flounder being the most accurately classified samples at 98 and 88%, respectively. Winter flounder from south‐west Nova Scotia (4X), an inshore sample from St Marys Bay and offshore fish from Browns Bank, had the lowest rates of correct classification (76 and 71%, respectively) due, primarily, to cross‐misclassification between the two samples. Winter pairwise comparisons of four microsatellite markers identified significant genetic differences between all populations sampled with the Georges Bank population being the most genetically distinct overall, and St Marys Bay and Browns Bank fish being the least dissimilar.

HELMINTH COMMUNITIES OF THE LESSER SANDEEL AMMODYTES TOBIANUS L. OFF THE WEST COAST OF IRELAND

The helminth parasites present in 412 lesser sandeels (Ammodytes tobianus) taken from June 1996 to May 1997 from the Aran Islands on the west coast of Ireland were examined. Ten helminth parasite species were recorded, and more than 92% of the sandeels were infected with at least 1 helminth species. Seven of the species were digeneans, including Brachyphallus crenatus, Hemiurus communis, Derogenes varicus, Lecithaster gibbosus, Opechona bacillaris, Cryptocotyle lingua, and Galactosomum lacteum; 2 nematodes, including Hysterothylacium sp. and Contracaecum sp.; and 1 cestode, Scolex pleuronectis. Three of the 7 digenean species were either larvae or immature. Only 2 species, the digeneans G. lacteum and H. communis, had prevalences greater than 50%. The dominant species was G. lacteum, accounting for 67% of all parasites present. The relationship between spawned groups, host length, and season versus the abundance, prevalence, species richness, and the total number of parasites in the infracommunities was investigated. No difference was found between the parasite communities of the 2 spawning races of the host population. Mean abundance and prevalence of the different parasite species showed seasonal variation. Numbers of parasite species and numbers of parasites increased with fish length. The role of A. tobianus as an intermediate host for helminths was assessed; it was determined that most were infectious to birds or mammals, with the majority of the parasite species being autogenic (infectious to fish). The mean number of parasites per fish was nearly a quarter of the value recorded for A. tobianus in the North Sea, where a much higher intensity of infection was recorded.