Invasion character and distribution of the Diplostomum huronense (La Rue, 1927) Hugnes, 1929 metacercariae in roach of Lake Ladoga

Estimation of the invasion character and distribution of the Diplostomum huronense metacercariae depending on the fish host age has been carried out in roach of Lake Ladoga. Distribution of D. huronense in the young roach (up to age 5+) is negative binomial. Aggregation of the parasite is caused not only by individual differences in the fish host resistance to the metacercariae invasion, but by a high mortality of hyperinfected fishes as well. In older individual hosts the host-parasite system is destroyed, and the parasite distribution approximates to normal. The parasite system of the diplostomids in roach is characterized by the spatial asymmetry, when most part of parasites inhabit few individual hosts, and probability of the case when a parasite get into previously infected host is higher than that of the invasion of parasite-free host. Thus, the Diplostomum huronense metacercaria is an important factor regulating the fish fry number both in direct (death of infected fry) and indirect (elimination of hyperinfected fishes by ichthyophagous birds) way.     

Metacercariae of Diplostomum spathaceum in the eyes of fishes from Yellowstone Lake, Wyoming

Fish were collected from Yellowstone Lake, Wyoming (USA). Metacercariae of Diplostomum spathaceum was found in the lens of 11 of 12 longnose suckers (Catostomus catostomus). The mean number of metacercariae per sucker was 59 and the average age of the fish was 11.6 yr. There was no correlation between age and intensity of parasites (r = 0.24). Of 10 cutthroat trout (Salmo clarki) examined, there were metacercariae present in six. The metacercariae were found outside of the lens tissue in the trout; they occurred in the vitreous humor and the retina. These may be a different species from those found in the suckers.     

Parasite fauna of the European river lamprey Lampetra fluviatilis (L.) from Lake Onega

Data on the parasite fauna of the adult European river lamprey Lampetra fluviatilis (L.) from Lake Onega are reported. Ten parasite species are found, including trematodes Diplostomum petromyzifluviatilis and D. spathaceum (metacercariae), cestode Proteocephalus longicollis, nematodes Cucullanus truttae and Raphidascaris acus, acanthocephalan Echinorhynchus salmonis, ectoparasitic infusoria Chilodonella hexastica, Trichodina tenuidens, and Trichodinella epizootica, and fungus Saprolegnia parasitica. Three species are found to be dominate, namely D. petromyzifluviatilis, Cucullanus truttae, and P. longicollis. Comparative analysis of the parasite faunas of the lampreys from other basins is carried out. Some similarity in the parasite faunas of lampreys and salmonids is discovered.     

Metacercariae of new trematode species of the genus Diplostomum (Trematoda,Diplostomidae) from fishes of Lake Tana,Ethiopia

Four new species of trematodes of the genus Diplostomum are described from metacercariae found in fishes from Lake Tana in Ethiopia: Diplostomum garrae sp. n. from the lens of Garra dembecha, D. longicollis sp. n. from the lens of Barbus humilis, D. montanum sp. n. from the lens of Barbus humilis, and D. tilapiae sp. n. from the vitreous body of Oreochromis niloticus. The metacercariae of the new species considerably differ in morphology and size from those of all known Holarctic species. It is the first African record of metacercariae of the genus Diplostomum in fish.     

On the development of body-wall musculature Diplostomum chromatophorum metacercariae (Trematoda: Diplostomidae)

The body-wall musculature of invasive cercariae and metacercariae of Diplostomum chromatophorum at different intervals after the penetration into the experimental intermediate host Cyprinus carpio (1, 3, 5, 6, 7, 10, 12, 20, 34, 40 days) has been investigated with the help of TEM technique. During the first 10 days after the invasion (in conditions of our experiment), the cercarial subtegumental muscle fibres degenerate. These muscles are replaced by newly formed ones. Mass differentiation of myoblasts beneath the tegument was observed in 7-10-day-old metacercariae. Obtained data indicate the metamorphosis of body-wall musculature during the morphogenesis in Diplostomum chromatophorum metacercariae.     

Infection status with trematode metacercariae in pond smelts, Hypomesus olidus

Many Koreans usually eat raw pond smelts, Hypomesus olidus, in the winter. This study was performed to evaluate the infection status with trematode metacercariae in pond smelts from January 1998 through February 1999. Among 1,305 fish collected, 459 were purchased from wholesale dealers in Chinchon-gun, Chungchongbuk-do, and the rest of them were caught with a casting net in Soyangho (Lake), Taehoman (Bay) and Paekkokchosuchi (Pond). Seven species of trematode metacercariae including two unidentified ones were detected from 1,305 pond smelts. The number of detected trematode metacercariae according to the species are as follow: Clonorchis sinensis 8, Holostephanus nipponicus 7, Cyathocotyle orientalis 24, Diplostomum sp. 14, and Metorchis orientalis 7. From the above results, it was confirmed that H. olidus plays a role as the second intermediate host of some kinds of trematode including C. sinensis in Korea. Our report shows possible clonorchiasis caused by eating raw pond smelts.     

Population dynamics of Tylodelphys destructor and Diplostomum mordax (Digenea: Diplostomidae) co-occurring in the brain of Patagonian silversides from Lake Pellegrini,Patagonia, Argentina

Studies on infection patterns of diplostomid parasites in commercially exploited fishes have not been done in Patagonia (Argentina). The aim of this work was to study the population dynamics of two diplostomid species in the brain of patagonian silversides (Odontesthes hatchery), the interaction between them, and effect on health and physical condition of the hosts. Tylodelphys destructor and Diplostomum mordax metacercariae in the brain of Patagonian silversides in Lake Pellegrini were studied between January 1991 and February 1992. Tylodelphys destructor parasitized all silversides examined; prevalence of D. mordax varied between 7% and 100%. Mean intensity for T. destructor was 35-140 and for D. mordax was 3-49. Highest mean intensities of T. destructor coincided with the lowest mean intensities of D. mordax. Recruitment seems to occur from July-November for T. destructor and from April-June for D. mordax, revealing a temporal segregation with inverse patterns of infection and recruitment. Tylodelphys destructor has higher intensities in the brain of the older fish, whereas D. mordax did not, suggesting another type of segregation. There were no evidences of gross pathology. No covariation between abundance of larvae and condition factor, gonadosomatic index, and gut fullness was detected.     

Histopathological and ultrastructural observations of metacercarial infections of Diplostomum phoxini (Digenea) in the brain of minnows Phoxinus phoxinus

The spatial distribution and histopathological changes induced by metacercariae of the digenean trematode Diplostomum phoxini (Faust, 1918) in the brains of European minnows Phoxinus phoxinus (L.) from the River Endrick, Scotland, were studied by light and electron microscopy. Post-mortem examination of a sample of 34 minnows revealed that 50% (n = 17) of the population was infected with 13.7 +/- 2.6 (mean +/- SE; range 1 to 38) metacercariae per infected host. Serial histological sections of the infected minnow brains revealed that the metacercariae were unevenly distributed throughout the brain, with aggregations occurring in the cerebellum, the medulla oblongata and the optic lobes. In fish with highest intensities of infection, over 40% of the cerebellar area and about 30% of the medulla oblongata area were occupied by larvae. Metacercariae disrupt the integrity of brain tissue, with individuals being found in small pockets surrounded by cellular debris. Metacercariae were rarely encountered on the surface of the brain. Electron microscopic examination of infection sites revealed that the granular layer surrounding metacercariae was necrotic, exhibited nuclear degradation and was marked by vacuolation of the cytoplasm. Rodlet cells, the only inflammatory cell types recorded in this study, were found only in parasitized brains and in close proximity to the teguments of metacercariae. It is hypothesised that secretions released from the teguments of metacercariae are a counter response to protect the metacercariae from the fish brain's cellular defence mechanisms.     

Observations on the occurrence of Diplostomum spathaceum and Schistocephalus sp. in ninespine sticklebacks (Pungitius pungitius) from the Belcher Islands, Northwest Territories, Canada

All 175 ninespine sticklebacks, Pungitius pungitius (Linné), collected from the Belcher Islands were parasitized by Diplostomum spathaceum (Rudolphi) and 43% by Schistocephalus sp. D. spathaceum metacercariae were mostly confined to a dorso-ventral band encircling the lens of the eye, and were concentrated in the anterio-dorsal sector of this band. The central area of the lens was thus relatively free of diplostomula, probably minimizing interference with the vision of the fish. The frequency distribution of D. spathaceum abundance in P. pungitius was closely approximated by a negative binomial, while that for Schistocephalus was best fitted by a Poisson. None of the fish condition factors examined appeared related to the intensity of the parasitic infections.     

Helminths of pond-reared walleye from Wisconsin

One hundred extended growth walleye fingerlings, Sander vitreus (Percidae), collected on 6 October 2004, from 1 rearing pond at the Lake Mills State Fish Hatchery in Lake Mills, Wisconsin, were examined for parasites. Diplostomum sp. (Trematoda: Diplostomatidae), Contracaecum sp. (Nematoda: Anisakidae), Bothriocephalus cuspidatus (Cestoda: Bothriocephalidae), and Proteocephalus sp. (Cestoda: Proteocephalidae) were the only parasites found. The first 3 species occurred as larval stages. Diplostomum sp. and Contracaecum sp. had similar prevalences, mean intensities, and mean abundances (72%, 2.2, and 1.6 and 71%, 2.1, 1.5, respectively) in walleye fingerlings. A headlamp technique used by the Wisconsin Department of Natural Resources personnel generated a prevalence of Diplostomum sp. in the lens that overestimated the prevalence of Diplostomum sp. found in a random subsample of 100 fingerlings examined with a microscope. Proteocephalus sp. and B. cuspidatus infected 14 and 12 fingerlings, respectively.     

Diversity and specificity in Diplostomum spp. metacercariae in freshwater fishes revealed by cytochrome c oxidase I and internal transcribed spacer sequences

In this study, sequences from the barcode region of cytochrome c oxidase I (COI) were used to distinguish Diplostomum spp. in a sample of 497 metacercariae collected from diverse fishes of the St. Lawrence River, Canada and findings were corroborated with internal transcribed spacer (ITS) regions of rDNA. Twelve species were detected based on sequences and metacercarial specificity for hosts and tissues. Although this is an unusually high diversity, additional species are likely to exist in the study area. Two species were indistinguishable with ITS data and there is evidence that they may be undergoing hybridization and/or have recently diverged. The ITS sequences of another species are similar to those of Diplostomum pseudospathaceum from Europe, but ITS data are insufficient to show that they are conspecific. Diplostomum spp. that infect tissues other than the lens are more host-specific than species inhabiting the lenses of fishes, which is attributed to the enhanced immunological privilege of the lens site compared with other tissues. Overall, COI sequences were superior to more commonly used ITS markers for delineating species of this important and taxonomically difficult pathogen.     

额尔齐斯河白斑狗鱼假尾复口吸虫的分子鉴定

利用分子生物学方法对采自额尔齐斯河（中国段）的白斑狗鱼（Esox lucius Linnaeus）晶状体内寄生的复口吸虫（Diplostomum）进行了种类鉴定,结果显示其种类为假尾复口吸虫（D.paracaudum）,为中国新记录种。通过PCR扩增待鉴定种的部分18S-ITS1-5.8S序列,测序后与GenBank中假尾复口吸虫的序列进行比对,发现其相似度达到99.6%。将该序列与7种复口吸虫的ITS1序列进行比对后构建系统进化树,进化树以单殖吸虫Gyrodactylus parvae为外类群,结果显示:待鉴定种与假尾复口吸虫（D.paracaudum）聚为一支,其支持率达到了50%以上,支持它们为同一虫种。     

The role of rodlet cells in the inflammatory response in Phoxinus phoxinus brains infected with Diplostomum

European minnows, Phoxinus phoxinus L., are commonly infected with Diplostomum phoxini Faust, 1918 metacercariae. A sub-sample of 34 minnows collected from the River Endrick, Stirlingshire, Scotland revealed that 50% of the population were infected (n = 17), with the cerebellum, medulla oblongata and the optic lobe regions of the minnow brain bearing the heaviest infections (13.7 +/- 2.6 mean +/- S.E.; 1-38 range). Serial histological sections through the brains of both uninfected and infected minnows revealed the presence of rodlet cells in the latter, which were occasionally observed in close proximity to the tegument of a metacercaria. Rodlet cells were the only type of host inflammatory cells found in this study and their role in the host's immune response to parasitic infection is commented upon.     

Infection status of pond smelts, Hypomesus olidus, and other freshwater fishes with trematode metacercariae in 6 large lakes

In order to determine the current infection status of pond smelts, Hypomesus olidus, and other freshwater fishes with trematode metacercariae, a total of 4,861 pond smelts and 18 other freshwater fishes, collected from the Soyang and Uiam Lakes in Gangwon-do, the Unam Lake in Jeollabuk-do, the Jangseong Lake in Jeollanam-do, the Uirim-ji (lake) in Chungcheongbuk-do, and the Andong Lake in Gyeongsangbuk-do, were individually digested with 1% pepsin-HCl and examined under a dissecting microscope. In all pond smelts caught from the 6 lakes, we were unable to detect any known human infectious trematode metacercariae in Korea. However, in other freshwater fishes, such as, Squalidus japonicus coreanus (Unam Lake), and Zacco platypus (Jangseong Lake) and Opsariichthys uncirostris amurensis (Jangseong Lake), metacercariae of human-infecting trematodes, i.e., Clonorchis sinensis and Metagonimus sp. were detected, respectively.     

Helminth communities of the rudd Scardinius erythrophthalmus (Cypriniformes, Cyprinidae) from Srebarna Biosphere Reserve, Bulgaria

A total of 180 individuals of Scardinius erythrophthalmus from Srebarna Lake, north-east Bulgaria, were examined for helminth parasites during spring, summer and autumn of 2005-2006 (30 specimens per season). Helminth parasites were recorded in 166 individuals (92.2%). Ten helminth species were found: trematodes--metacercariae of Posthodiplostomum cuticola, Diplostomum chromatophorum and D. spathaceum; monogeneans--Dactylogyrus difformis, D. difformoides and Diplozoon scardinii; cestodes--metacestodes of Paradilepis scolecina; nematodes--larvae of Spiroxys contortus and Rhabdochona denudata and adults of Schulmanela petruschewskii. Significant seasonal differences in the mean abundance were recorded for D. difformis, D. difformoides and D. scardinii. Significant seasonal differences in prevalence were recorded for P. cuticola, D. difformis, D. difformoides and D. scardinii. Dominant species in the component communities were P. cuticola, D. difformis and D. difformoides. The species composition of the component community essentially differs from that in the adjacent Danube River; a possible reason is the specific hydrobiological situation of the lake, characterized by a low density of benthic molluscs and crustaceans.     

No strict host specificity: Brain metacercariae Diplostomum petromyzifluviatilis Müller (Diesing, 1850) are conspecific with Diplostomum sp. Lineage 4 of Blasco-Costa et al. (2014)

Metacercariae of Diplostomum petromyzifluviatilis (Digenea, Diplostomidae) from the brain of European river lamprey Lampetra fluviatilis from the Baltic Sea basin and Arctic lamprey Lethenteron camtschaticum from the White Sea basin were studied with the use of genetic and morphological methods. Phylogenetic analysis based on cox1 marker showed that the parasites of both lamprey species were conspecific with Diplostomum sp. Lineage 4 of Blasco-Costa et al. (2014). The name Diplostomum petromyzifluviatilis Müller (Diesing, 1850) has historical precedence as a species described from the brain of lampreys and should be used in genus nomenclature. There were no morphological qualitative differences between the metacercariae from the two lamprey species but those from L. fluviatilis were larger than those from L. camtschaticum. We expanded the data on the second intermediate hosts and the localization of D. petromyzifluviatilis, showing that its metacercariae occur not only in the brain of lampreys but also in the brain and the retina of three-spined stickleback Gasterosteus aculeatus and the vitreous humour of the perch Perca fluviatilis across the European part of the Palearctic.     

Prevalence of two site-specific populations of Diplostomum spp. in eye infections of rainbow trout, Salmo gairdneri Richardson, from lakes in Washington State, U.S.A.

Two distinct site-specific populations of Diploslomum spp., occurring concurrently in the lens and retina of naturally infected rainbow trout, were different morphologically. They represent separate populations epidemiologically. The lens and retina metacercariae did not differ immunologically when tested by an enzyme-linked immunosorbent assay against immune rabbit and trout antisera. Antibody titres became positive by September 1982 in a natural population of yearling rainbow trout infected with lens and retina metacercariae and remained positive for at least 8 months. The antibodies formed may offer protection against reinfections with Diplostomum spp. cercariae.     

The epidemiology of the metacercariae of Diplostomum baeri and D. spathaceum in perch (Perca fluviatilis) from the warm water effluent of a nuclear power station

Thermal effects on the dynamics of infection with metacercariae of Diplostomum baeri and D. spathaceum were monitored between May and September, in a year-class of perch Perca fluviatilis, in an artificial lake receiving warm water discharges from a nuclear power station and in an unheated reference site, for a two year period. In the heated area the prevalence of infection of the retinal form, D. baeri, was always 100%, whereas in the unheated site there was an increase from 93% in May to 100% in June 1986. The relative density of D. baeri was found to increase gradually during the first summer in both areas, although the accumulation rate of metacercariae was significantly increased in the heated area. In August of the first year the relative density of D. baeri peaked in the heated area, whereas it continued to increase in the unheated control. However, in September of the following year, the relative densities were at the same level in both thermal regimes. A concomitant decline in the degree of overdispersion of metacercariae within the host population was observed in the heated area as the population density of metacercariae decreased, whereas the index of dispersion remained at the same level throughout the study in the unheated area. However, it was not possible to sample perch in the unheated area between October 1986 and May 1987 and changes in the parasite population could have occurred during this period. The prevalence and relative density of D. spathaceum, the lens form, was on the contrary low, especially in the unheated site where it was recorded only occasionally. The infection of D. baeri exhibited a convex pattern in both thermal regimens, although the peak infection was noticed earlier in the heated area. Regulation of the parasite infrapopulation may have been achieved by the combined effects of a decreased transmission rate of cercariae with increasing age of the host, the mortality of metacercariae as a natural termination of the life span and to selective predation of heavily infected hosts. However, regardless of an increased accumulation rate of metacercariae in the heated area, the relative densities of D. baeri became equal in both thermal regimes at the end of the study. The mortality rate of metacercariae in the heated area was therefore presumably increased as compared with the unheated reference site.     

Identification of Diplostomum spp. in the retina of perch Perca fluviatilis and the lens of roach Rutilus rutilus from the Baltic Sea — an experimental study

Metacercariae of the genus Diplostomum dwelling in the retina of perch Perca fluviatilis and the lens of roach Rutilus rutilus were identified on the basis of adults obtained by feeding various piscivorous birds of the families Laridae, Anatidae and Phasianidae with metacercariae on an experimental basis. Both morphological studies of the metacercariae and adults obtained from the intestine of the infected birds, as well as the suitability in these hosts, indicated that we were dealing with two different species of Diplostomum. The perch form was recognised as D. baeri Dubois, 1937. Although metacercariae of this species matured both in herring gull Larus argentatus and common tern Sterna hirundo, the principal final host seemed to be goosanders Mergus merganser. In contrast, the lens form in roach was identified as D. spathaceum (Rudolphi, 1819) and it seemed to be restricted to birds of the family Laridae. These experimental results agree with parasitological findings from birds infected in the wild.