ABSTRACT
Nematomorph parasites manipulate terrestrial arthropods to enter streams where the parasites reproduce. These manipulated arthropods become a substantial prey subsidy for stream salmonids, causing cross-ecosystem energy flow. Diverse nematomorph-arthropod associations underlie the energy flow, but it remains unknown whether they can mediate the magnitude and temporal attributes of the energy flow. Here, we investigated whether distinct phylogenetic groups of nematomorphs manipulate different arthropod hosts and mediate seasonal prey subsidy for stream salmonids. The results of our molecular-based diagnoses show that Gordionus and Gordius nematomorphs infected ground beetle and orthopteran hosts, respectively. The presumable ground beetle hosts subsidized salmonid individuals in spring, whereas the presumable orthopteran hosts did so in autumn. Maintaining the two distinct nematomorph-arthropod associations thus resulted in the parasite-mediated prey subsidy in both spring and autumn in the study streams. Manipulative parasites are common, and often associated with a range of host lineages, suggesting that similar effects of phylogenetic variation in host-parasite associations on energy flow might be widespread in nature.
Subject(s)
Ecosystem , Host-Parasite Interactions , Seasons , Animals , Salmonidae/parasitology , Phylogeny , Helminths/physiology , Coleoptera/parasitology , Coleoptera/physiology , RiversABSTRACT
Between 1898 and 1940, eight human cases of diphyllobothriasis were reported in Argentina, always in recently arrived European immigrants. In 1982, the first autochthonous case was detected, and since then, 33 other autochthonous cases have been reported, totaling 42 cases of human diphyllobothriasis in Argentina before the present study. Our aim is to update the information on diphyllobothriasis in Argentina by identifying specimens from new cases using morphometrical and/or molecular methods. We also aim to assess the epidemiological relevance of this food-borne disease in the country. Anamnestic data were obtained from patients or professionals, along with 26 worms identified using morphometrical (21 samples) and molecular techniques (5 samples). All the patients acquired the infection by consuming freshwater salmonids caught in Andean lakes in Northern Patagonia. Morphometrics and DNA markers of worms were compatible with Dibothriocephalus latus. In total, 68 human cases have been detected in Argentina, 60 of which were autochthonous. The human population living North-western Patagonia, whose lakes are inhabited by salmonids, is increasing. Similarly, the number of other definitive hosts for Dibothriocephalus dendriticus (gulls) and for D. latus (dogs) is also increasing. In addition, salmonid fishing and the habit of consuming home-prepared raw fish dishes are becoming widespread. Therefore, it is to be expected that diphyllobothriasis in Argentina will increase further.
Subject(s)
Diphyllobothriasis , Diphyllobothrium , Argentina/epidemiology , Diphyllobothriasis/epidemiology , Diphyllobothriasis/parasitology , Humans , Animals , Male , Female , Diphyllobothrium/genetics , Diphyllobothrium/isolation & purification , Diphyllobothrium/classification , Adult , Middle Aged , Aged , Salmonidae/parasitology , Foodborne Diseases/parasitology , Foodborne Diseases/epidemiology , Young Adult , History, 20th Century , History, 19th CenturyABSTRACT
Parasitic salmon lice (Lepeophtheirus salmonis) are a constraint to the sustainable growth of salmonids in open net pens, and this issue has caused production to level off in recent years in the most aquaculture-intensive areas of Norway. The maximum allowed biomass at a regional level is regulated by using the so-called "traffic light" system, where salmon louse-induced mortality of migrating wild salmon post-smolts is evaluated against set targets. As a case study, we have investigated how a specific aquaculture-intensive area can reduce its louse levels sufficiently to achieve a low impact on wild salmon. Analyses of the output from a virtual post-smolt model that uses data on the reported number of salmon lice in fish farms as key input data and estimates the salmon louse-induced mortality of wild out-migrating Atlantic salmon post-smolts, suggested that female louse abundance on the local farms must be halved in spring to reach the goal implied by the traffic light system. The outcome of a modelling scenario simulating a proposed new plan for coordinated production and fallowing proved beneficial, with an overall reduction in louse infestations and treatment efforts. The interannual variability in louse abundance in spring, however, increased for this scenario, implying unacceptably high louse abundance when many farms were in their second production year. We then combined the scenario with coordinated production with other louse control measures. Only measures that reduced the density of farmed salmonids in open cages in the study area resulted in reductions in salmon louse infestations to acceptable levels. This could be achieved either by stocking with larger fish to reduce exposure time or by reducing fish numbers, e.g. by producing in closed units.
Subject(s)
Aquaculture , Copepoda , Fish Diseases , Animals , Fish Diseases/parasitology , Fish Diseases/prevention & control , Copepoda/physiology , Aquaculture/methods , Norway , Female , Ectoparasitic Infestations/veterinary , Ectoparasitic Infestations/parasitology , Ectoparasitic Infestations/prevention & control , Salmo salar/parasitology , Salmonidae/parasitology , Salmon/parasitologyABSTRACT
The article dwells upon characteristics of the species richness of parasite communities in least cisco Coregonus sardinella Valenciennes in Polar water bodies: Kureyskoye Reservoir, Lake Kutaramakan, Khatanga River. The communities consist of parasite species common in coregonids. The main species in all the parasite communities in least cisco are Dibothriocephalus ditremus and D. dendriticus. Triaenophorus crassus plerocercoids dominate in the regulated water body (Kureyskoye Reservoir). To analyze the species richness of the component communities (s), coefficients of the power-law equation s = a × nb were applied, where a is the expected species richness in the first host individual examined, and b is the rate of species accumulation in parasite component communities (s). The resulting curves of species accumulation give statistical rigor to the assessment of differences and similarities of the species richness of the component communities of parasites in least cisco of various ages and habitats. The species richness of infra- and component parasite communities in least cisco was found to be significantly lower in the lake and the storage reservoir than in riverine habitats (Khatanga River). At the same time, the species accumulation rate for parasite communities in least cisco from Lake Kutaramakan was higher than in the reservoir due to a higher diversity of parasite infracommunities.
Subject(s)
Parasites , Salmonidae , Animals , Cold Climate , Salmonidae/parasitology , Ecosystem , WaterABSTRACT
New data on the complete mitochondrial genome of Azygia robusta (Azygiidae) were obtained by the next-generation sequencing (NGS) approach. The mitochondrial DNA (mtDNA) of A. robusta had a length of 13 857 bp and included 12 protein-coding genes, two ribosomal genes, 22 transfer RNA genes, and two non-coding regions. The nucleotide sequences of the complete mitochondrial genomes of two A. robusta specimens differed from each other by 0.12 ± 0.03%. Six of 12 protein-coding genes demonstrated intraspecific variation. The difference between the nucleotide sequences of the complete mitochondrial genomes of A. robusta and Azygia hwangtsiyui was 26.95 ± 0.35%; the interspecific variation of protein-coding genes between A. robusta and A. hwangtsiyui ranged from 20.5 ± 0.9% (cox1) to 30.7 ± 1.2% (nad5). The observed gene arrangement in the mtDNA sequence of A. robusta was identical to that of A. hwangtsiyui. Codon usage and amino acid frequencies were highly similar between A. robusta and A. hwangtsiyui. The results of phylogenetic analyses based on mtDNA protein-coding regions showed that A. robusta is closely related to A. hwangtsiyui (belonging to the same suborder, Azygiida) that formed a distinct early-diverging branch relative to all other Digenea. A preliminary morphological analysis of paratypes of the two azygiid specimens studied showed visible morphological differences between them. The specimen extracted from Sakhalin taimen (Parahucho perryi) was most similar to A. robusta. Thus, we here provide the first record of a new definitive host, P. perryi, for A. robusta and also molecular characteristics of the trematode specimens.
Subject(s)
Salmonidae , Trematoda , Phylogeny , Salmonidae/parasitology , Animals , DNA, Mitochondrial/chemistry , Sequence Analysis, DNA , Russia , Trematoda/anatomy & histology , Trematoda/classification , Trematoda/genetics , Trematoda/isolation & purificationABSTRACT
OBJECTIVE: The ability to effectively treat parasitic infestations of fish is of high importance for fish culture facilities. However, tools or approved therapies for treating infestations on fish are limited. This paper summarizes results from four separate clinical field studies that evaluated the efficacy of hydrogen peroxide (H2 O2 ; 35% PEROX-AID) for reducing Gyrodactylus spp. infestation density. METHODS: Three species of Gyrodactylus were studied (G. salmonis, hosts: Brook Trout Salvelinus fontinalis and Lake Trout S. namaycush; G. freemani, host: Yellow Perch Perca flavescens; G. hoffmani, host: Fathead Minnow Pimephales promelas) before and after the application of immersion H2 O2 therapy. RESULT: Parasite density was significantly reduced for each parasite × host combination to which H2 O2 therapy was applied. Two clinical field studies in salmonids were found to demonstrate substantial effectiveness that enabled 35% PEROX-AID approval. CONCLUSION: Further assessments of Gyrodactylus spp. could expand the use of H2 O2 for controlling these parasites in aquaculture. Specifically, H2 O2 was effective at all levels tested (50 or 75 mg H2 O2 /L for 60 min for the Yellow Perch and Fathead Minnow clinical field studies; 100 or 150 mg H2 O2 /L for 30 min regardless of salt pre-treatment for the Brook Trout study; and 100 mg H2 O2 /L for 30 min or 50 mg H2 O2 /L for 60 min for the Lake Trout study).
Subject(s)
Cyprinidae , Fish Diseases , Perches , Salmonidae , Trematoda , Animals , Hydrogen Peroxide , Salmonidae/parasitology , Trout , Fish Diseases/drug therapy , Fish Diseases/parasitologyABSTRACT
High-throughput sequencing strategies became commonly employed to study non-model parasites, but the corresponding genomes and transcriptomes were seldom mined following the original publication. Similar to the data generated with genome skimming techniques based on shallow-depth shotgun genomes, various genomic and transcriptomic resources can be screened for useful molecular phylogenetic markers traditionally characterised with Sanger sequencing. Here, we provide an example of a strategy using reduced-representation genomic as well as transcriptomic data to obtain broad insights into the molecular diversity of the cestode Proteocephalus longicollis, a common parasite of salmonids distributed throughout the Holarctic region. We extract popular mitochondrial and nuclear ribosomal markers from various genomic resources for hundreds of parasite specimens from multiple European whitefish populations and compare those with Proteocephalus representatives from other species of salmonids and various geographical regions. In contrast with the previous morphology-based assessments, molecular phylogeny reveals a high degree of genetic divergence between Proteocephalus isolates from different salmonids, contrastingly low genetic differentiation within the parasite's populations hosted by the European whitefish (Coregonus lavaretus species complex), and a sister species relationship of Proteocephalus from European whitefish and Proteocephalus percae, a parasite of European perch (Perca fluviatilis). Proteocephalus spp. from North American lake whitefish, brown trout and Arctic charr each formed clearly distinct lineages. These results advance our understanding of the interrelationships of the Proteocephalus-aggregate, a well-recognized clade of Holarctic freshwater fish proteocephalids, and support resurrection of some of the nominal species of Proteocephalus, including Proteocephalus exiguus La Rue, 1911 from North American coregonids and Proteocephalus fallax La Rue, 1911 from European C. lavaretus, reserving Proteocephalus longicollis (Zeder, 1800) exclusively for parasites of Salmo trutta.
Subject(s)
Cestoda , Fish Diseases , Salmonidae , Animals , Phylogeny , Fish Diseases/parasitology , Salmonidae/parasitology , GenomicsABSTRACT
Ceratonova shasta is a myxozoan parasite endemic to the Pacific Northwest of North America that is linked to low survival rates of juvenile salmonids in some watersheds such as the Klamath River basin. The density of C. shasta actinospores in the water column is typically highest in the spring (March-June), and directly influences infection rates for outmigrating juvenile salmonids. Current management approaches require quantities of C. shasta density to assess disease risk and estimate survival of juvenile salmonids. Therefore, we developed a model to simulate the density of waterborne C. shasta actinospores using a mechanistic framework based on abiotic drivers and informed by empirical data. The model quantified factors that describe the key features of parasite abundance during the period of juvenile salmon outmigration, including the week of initial detection (onset), seasonal pattern of spore density, and peak density of C. shasta. Spore onset was simulated by a bio-physical degree-day model using the timing of adult salmon spawning and accumulation of thermal units for parasite development. Normalized spore density was simulated by a quadratic regression model based on a parabolic thermal response with river water temperature. Peak spore density was simulated based on retained explanatory variables in a generalized linear model that included the prevalence of infection in hatchery-origin Chinook juveniles the previous year and the occurrence of flushing flows (≥171 m3/s). The final model performed well, closely matched the initial detections (onset) of spores, and explained inter-annual variations for most water years. Our C. shasta model has direct applications as a management tool to assess the impact of proposed flow regimes on the parasite, and it can be used for projecting the effects of alternative water management scenarios on disease-induced mortality of juvenile salmonids such as with an altered water temperature regime or with dam removal.
Subject(s)
Parasites , Parasitic Diseases, Animal , Salmonidae , Animals , Parasitic Diseases, Animal/epidemiology , Salmon/parasitology , Salmonidae/parasitology , WaterABSTRACT
The genus Salmincola is an ectoparasitic copepod group commonly infesting the branchial and buccal cavities of salmonids. While negative impacts on hatchery fishes have been reported, their impacts on wild fish populations and distribution patterns are critically understudied. In the Shiretoko Peninsula, Hokkaido, Japan, we found parasites belonging to this genus on the branchial cavity of a stream salmonid, Southern Asian Dolly Varden Salvelinus curilus. All parasites recovered were identified as Salmincola edwardsii based on morphological characteristics and partial 28S rDNA sequences. Prevalence was highly heterogeneous even among neighboring streams (0-54.8%, < 10 km) with the mean intensity among streams being generally low (2.19 parasites/infeted fish). Despite the low intensity, quantile regression analysis showed negative trends between parasite intensity and host condition, suggesting that the infestation of S. edwardsii has a potential negative impact on the host salmonid. In addition, a single copepod was found from an anadromous fish, which could indicate some salinity tolerance of the copepods. It is important to evaluate the effects of Salmincola spp. on host species and determine the limiting factors on the parasite's distribution for proper management.
Subject(s)
Copepoda/pathogenicity , Fish Diseases/parasitology , Parasitic Diseases, Animal/parasitology , Salmonidae/parasitology , Animals , Copepoda/anatomy & histology , Copepoda/genetics , Fish Diseases/epidemiology , Japan/epidemiology , Parasitic Diseases, Animal/epidemiologyABSTRACT
Norway produces more than one million tonnes of salmonids every year, almost exclusively in open-water net pens. In 2014, the Norwegian government announced plans to increase salmonid production. However, increasing the number of farmed salmonids can have negative effects on the marine environment that threaten the industry's sustainability. In particular, production growth can lead to an increase in density-dependent diseases, including parasitic sea lice. The aim of this study was to simulate the effects of increased salmonid production on sea lice abundance using different scenarios for increasing the number of fish and for the management of sea lice. We used a previously developed, partly stage-structured model based on Norwegian production and environmental data to simulate the different scenarios. Our results show that increasing the marine farmed salmonid population at a national level by two or five times the current production leads to an increase in the sea lice abundance by 3.5% and 7.1%, respectively. We also found that by lowering the maximum allowable level of sea lice to an average of 0.049 adult females per fish, weekly treatments can be used to control sea lice population growth with a five times increase in production. However, this increases the number of farms treating per week by as much as 281.3%, which can lead to high costs and increased mortality among farmed salmonids. Overall, the results from our study shed light on the effects of increasing salmonid production in Norway with respect to the ongoing threat of sea lice infestations.
Subject(s)
Copepoda , Fish Diseases , Lice Infestations , Salmonidae , Animals , Female , Fish Diseases/epidemiology , Fish Diseases/parasitology , Norway/epidemiology , Salmonidae/parasitologyABSTRACT
Lake Teletskoye (West Siberia, Russia) is inhabited by a sympatric pair of whitefish, with each member of the pair being characterized by different feeding habits. Coregonus lavaretus pidschian (Gmelin, 1789) is a large 'benthivorous' form, while C. l. pravdinellus (Dulkeit, 1949) is a small 'planktivorous' form. Fish were collected from the end of August to the middle of September in 2017 and 2019-2020 in the north part of Lake Teletskoye. For the 'benthivorous' form the prevalence, intensity and abundance of T. crassus ranged from 22.4% to 51.9%, 1.9-2.8 and 0.4-1.3, respectively, whereas the same indices for the 'planktivorous' form ranged from 94.7% to 97.5%, 4.2-4.8 and 4.0-4.7, respectively. The level of prevalence of infection and abundance of T. crassus in muscle was relatively stable among studied years for both forms. The level of prevalence was higher in the years 2019 and 2020 than in 2017 for the 'benthivorous' form, whereas for the 'planktivorous' form this index did not change during the studied years. For the first time, a partial sequencing of the cox1 gene (593 bp) for T. crassus was sequenced. All 15 plerocercoids of T. crassus were represented by four haplotypes.
Subject(s)
Cestoda , Diet/veterinary , Fish Diseases , Salmonidae , Animals , Cestoda/genetics , Fish Diseases/parasitology , Lakes , Muscles/parasitology , Salmonidae/parasitology , SiberiaABSTRACT
During their different life stages, parasites undergo remarkable morphological, physiological, and behavioral "metamorphoses" to meet the needs of their changing habitats. This is even true for ectoparasites, such as the monogeneans, which typically have a free-swimming larval stage (oncomiracidium) that seeks out and attaches to the external surfaces of fish where they mature. Before any obvious changes occur, there are ultrastructural differences in the oncomiracidium's outer surface that prepare it for a parasitic existence. The present findings suggest a distinct variation in timing of the switch from oncomiracidia epidermis to the syncytial structure of the adult tegument and so, to date, there are three such categories within the Monogenea: (1) Nuclei of both ciliated cells and interciliary cytoplasm are shed from the surface layer and the epidermis becomes a syncytial layer during the later stages of embryogenesis; (2) nuclei of both ciliated cells and interciliary syncytium remain distinct and the switch occurs later after the oncomiracidia hatch (as in the present study); and (3) the nuclei remain distinct in the ciliated epidermis but those of the interciliary epidermis are lost during embryonic development. Here we describe how the epidermis of the oncomiracidium of Discocotyle sagittata is differentiated into two regions, a ciliated cell layer and an interciliary, syncytial cytoplasm, both of which are nucleated. The interciliary syncytium extends in-between and underneath the ciliated cells and sometimes covers part of their apical surfaces, possibly the start of their shedding process. The presence of membranous whorls and pyknotic nuclei over the surface are indicative of membrane turnover suggesting that the switch in epidermis morphology is already initiated at this stage. The body tegument and associated putative sensory receptors of subadult and adult D. sagittata are similar to those in other monogeneans.
Subject(s)
Epidermis/ultrastructure , Fish Diseases/parasitology , Salmonidae/parasitology , Trematoda/ultrastructure , Trematode Infections/veterinary , Animals , Cell Nucleus/ultrastructure , Cytoplasm/ultrastructure , Epidermis/growth & development , Gills/parasitology , Larva/ultrastructure , Trematoda/growth & development , Trematode Infections/parasitologyABSTRACT
Salmincola californiensis is a Lernaeopodid copepod parasitizing Pacific salmon and trout of the genus Oncorhynchus. Salmincola californiensis is of increasing concern in both native and introduced ranges because of its potential fish health impacts and high infection prevalence and intensity in some systems. Discrepancies in the documented life history phenology of S. californiensis with the sister species Salmincola edwardsii, as well as our laboratory observations, led us to question the existing literature. We documented a naupliar stage, thought lost for S. californiensis. In addition, we found a high degree of thermal sensitivity in egg development, with eggs developing faster under warmer conditions. Survival of copepodids was also highly dependent on temperature, with warmer conditions reducing lifespan. The longest lived copepodid survived 18 days at 4°C in stark contrast to the generally accepted <48 h survival for that life stage. We also note a consistent relationship between egg sac size and the number of eggs contained. However, egg sac sizes were highly variable. Our findings demonstrate that revisiting old assumptions for S. californiensis and related taxa will be a necessary step to improving our knowledge of the parasite life history and development that will be critical to disease management.
Subject(s)
Copepoda , Life Cycle Stages/physiology , Salmonidae/parasitology , Animals , Copepoda/growth & development , Copepoda/physiology , Ectoparasitic Infestations/veterinary , Fish Diseases/parasitology , Gills/parasitology , Oncorhynchus mykiss/parasitology , Salmon/parasitology , TemperatureABSTRACT
Myxozoans are parasitic, microscopic cnidarians that have retained the phylum-characteristic stinging capsules called nematocysts. Free-living cnidarians, like jellyfish and corals, utilize nematocysts for feeding and defence, with discharge powered by osmotic energy. Myxozoans use nematocysts to anchor to their fish hosts in the first step of infection, however, the discharge mechanism is poorly understood. We used Myxobolus cerebralis, a pathogenic myxozoan parasite of salmonid fishes, and developed two assays to explore the nature of its nematocyst discharge. Using parasite actinospores, the infectious stage to fish, we stimulated discharge of the nematocysts with rainbow trout mucus in vitro, in solutions enriched with chloride salts of Na+, K+, Ca2+ and Gd3+, and quantified discharge using microscopy. We then used quantitative polymerase chain reaction to evaluate the in vivo effects of these treatments, plus Mg2+ and the common aquaculture disinfectant KMnO4, on the ability of M. cerebralis actinospores to infect fish. We found that Mg2+ and Gd3+ reduced infection in vivo, whereas Na+ and K+ over-stimulated nematocyst discharge in vitro and reduced infection in vivo. These findings align with nematocyst discharge behaviour in free-living Cnidaria, and suggest phylum-wide commonalties, which could be exploited to develop novel approaches for controlling myxozoan diseases in aquaculture.
Subject(s)
Cations, Monovalent/metabolism , Myxobolus/physiology , Nematocyst/metabolism , Animals , Biological Evolution , Cnidaria , Fish Diseases/parasitology , Fish Diseases/transmission , Host-Parasite Interactions , Myxozoa/physiology , Oligochaeta/parasitology , Salmonidae/parasitologyABSTRACT
In 2018 and 2019, salmonid fishes, Salmo trutta L. and Salvelinus alpinus (L.) from lakes in Iceland were assessed for trematodes during a parasitological examination. Combined morphological and molecular analyses revealed the presence of four trematode species, two of which were previously known to parasitise salmonids in Iceland, Crepidostomum farionis (Müller, 1780) and Phyllodistomum umblae (Fabricius, 1780), and the two remaining species were recognised as new to science. Morphologically and genetically, Crepidostomum brinkmanni n. sp. and C. pseudofarionis n. sp. are closely related to two European species, namely C. metoecus and C. farionis. However, C. brinkmanni n. sp. is distinct by the position of maximum body width and arrangement of vitelline follicles; C. pseudofarionis n. sp. is distinct by its stout body, position of maximum body width, size of muscular papillae relative to oral sucker and the anterior extent of vitelline follicles. The new species were previously molecularly detected in their intermediate and definitive hosts in Norway and Ukraine, but their sequences were not supplemented with any morphological characterisation. In the present study, we provide detailed morphological descriptions and molecular sequences (28S rDNA and ITS2) of the four species of trematodes detected in Iceland. The discovery of the two new species of Crepidostomum indicates that the trematode diversity in fishes in the north is higher than previously known; our finding doubles the species spectrum of fish trematodes for Iceland. The record of C. brinkmanni from Ukraine indicates that its distribution might not be limited to northern latitudes.
Subject(s)
Biodiversity , Fish Diseases/parasitology , Salmonidae/parasitology , Trematoda/classification , Trematode Infections/parasitology , Animals , DNA, Ribosomal/genetics , Fish Diseases/epidemiology , Iceland/epidemiology , Lakes , Phylogeny , Species Specificity , Trematoda/genetics , Trematode Infections/epidemiologyABSTRACT
Changes in parasite communities might result in new host-parasite dynamics and may threaten local fish populations. This phenomenon has been suggested for acanthocephalan parasites in the river Rhine and Danube where the species Pomphorhynchus tereticollis is becoming replaced by the Ponto-Caspian P. laevis. Developing knowledge on morphologic, genetic and behavioural differences between such species is important to follow such changes. However, disagreements on the current phylogeny of these two acanthocephalan species are producing conflicts that is affecting their correct identification. This study is offering a clearer morphological and genetic distinction between these two species. As P. tereticollis is found in rhithral tributaries of the Rhine, it was questioned whether the local salmonid populations were hosts for this species and whether P. laevis was expanding into the Rhine watershed as well. In order to test for this, brown trout, Salmo trutta, and grayling, Thymallus thymallus from South-Western Germany watersheds have been samples and screened for the occurrence of acanthocephalan parasites. For the first time, both species were confirmed to be hosts for P. tereticollis in continental Europe. P. tereticollis was found to be common, whereas P. leavis was found only at a single location in the Danube. This pattern suggest either that the expansion of P. laevis through salmonid hosts into rhithral rivers has not yet occurred, or that not yet ascertained biotic or abiotic features of rhithral rivers hinder P. laevis to spread into these areas.
Subject(s)
Acanthocephala/genetics , Fish Diseases/parasitology , Salmonidae/parasitology , Acanthocephala/anatomy & histology , Acanthocephala/classification , Animals , DNA, Helminth/genetics , DNA, Helminth/metabolism , Fish Diseases/epidemiology , Fish Diseases/pathology , Germany/epidemiology , Microscopy, Electron, Scanning , Phylogeny , Prevalence , Trout/parasitologyABSTRACT
Proliferative kidney disease (PKD) of salmonids, a chronic immunopathology caused by the myxozoan parasite Tetracapsuloides bryosalmonae, is exacerbated by increased water temperatures. PKD causes economic concerns to trout farmers and contributes to the decline of wild salmonid populations in North America and Europe. The parasite occurs as far north as Norway and Iceland in Europe and was confirmed from California to southern British Columbia in the American continent. In mid-September 2011 adult chum salmon (Oncorhynchus keta) were sampled from Kantishna River, a tributary to Yukon River in Alaska. Clinical PKD was diagnosed based on the macroscopic appearance of mottled kidneys that were uniformly swollen and by the detection of tumultuous histozoic extrasporogonic and coelozoic sporogonic stages of T. bryosalmonae in renal tissue by histopathology. Archived samples provided the molecular confirmation and local strain identification, representing the first confirmed case of PKD in wild adult chum salmon, also co-infected with Parvicapsula minibicornis that represents another novel myxozoan detection in Alaska. Our investigation was extended to another case from August/September 1997, with mortality following furunculosis and ectoparasite co-infections, in sockeye salmon (Oncorhynchus nerka) pre-smolts net-pen reared in English Bay Lakes, Alaska. Immunohistochemistry on archived histological preparations confirmed T. bryosalmonae sporogonic and extrasporogonic stages, indicating a severe to resolving PKD, with concomitant Chloromyxum spp. infection. Those cases provide the first documentation that this parasite is present in Alaska and causes PKD in wild and cultured salmonids in the region. The known geographic range of T. bryosalmonae can be extended to ~267 km south of the Arctic Circle, representing the northernmost detection in America. Given the vast size of Alaska and small resident population, it is likely that T. bryosalmonae remained undetected, but more recently became evident due to the clinical manifestation of PKD, possibly linked to increasing water temperatures reported at the sample locations.
Subject(s)
Fish Diseases , Kidney Diseases , Myxozoa , Parasitic Diseases, Animal , Salmonidae , Alaska , Animals , Fish Diseases/parasitology , Kidney , Kidney Diseases/parasitology , Myxozoa/pathogenicity , Salmonidae/parasitologyABSTRACT
The myxozoan parasite Ceratonova shasta is an important pathogen that infects multiple species of Pacific salmonids. Ongoing genetic surveillance has revealed stable host-parasite relationships throughout the parasite's endemic range. We applied Bayesian phylogenetics to test specific hypotheses about the evolution of these host-parasite relationships within the well-studied Klamath River watershed in Oregon and California, USA. The results provide statistical support that different genotypes of C. shasta are distinct lineages of one species, which is related to two other Ceratonova species in the same ecosystems; Ceratonova X in speckled dace and C. gasterostea in threespine stickleback. Furthermore, we found strong support for the hypothesis that C. shasta type 0 in native steelhead trout and type I in Chinook salmon each evolved with a specialist host adaptation strategy, while C. shasta type II in coho salmon resulted from a generalist host adaptation strategy. Inferred date and host species of the most recent common ancestor of extant Klamath basin types indicate that it occurred between 14,000 and 21,000â¯years ago, and most likely infected a native steelhead or rainbow trout host.
Subject(s)
Myxozoa/classification , Salmonidae/parasitology , Sequence Analysis, DNA/methods , Adaptation, Physiological , Animals , Bayes Theorem , California , Genotype , Host Specificity , Host-Parasite Interactions , Myxozoa/genetics , Myxozoa/physiology , Oregon , Phylogeny , Salmonidae/geneticsABSTRACT
BACKGROUND: Rhadinorhynchus trachuri Harada, 1935 is probably one of the most widely distributed acanthocephalans in the world, but the least known taxonomically. This report fills the large gap of knowledge about its taxonomy, host relationships, and worldwide distribution in marine fishes of both sides of the Pacific Ocean and the connecting Indian Ocean. PURPOSE: To revisit the taxonomy of this species, provide a more complete morphological description and expand our knowledge about its morphological identity and variations and elaborate on its worldwide zoogeography; accounting for its worldwide distribution based on new collections, museum specimens, and on published reports. METHODS: Specimens from Vietnam were processed, identified, and documented using standard techniques. Specimens of R. trachuri were studied from three species of fish in three families, Auxis thazard (Lacépède) (Scombridae), Megalaspis cordyla (Linn.) (Carangidae), and Tylosurus sp. (Belonidae) in Nha Trang and Binh Thuan in the south Pacific coast of Vietnam and additional museum specimens mostly from salmonids from the Pacific coast of California were also studied. Extensive research was conducted on published records of R. trachuri and its marine fish hosts worldwide. RESULTS: Specimens of R. trachuri are characterized by cylindrical trunk with anterior rings of spines and posterior ventral and lateral spines, a proboscis usually with 12 hook rows each with 19-24 hooks, variable position of testes, and a long uterus, uterine bell attached to the dorsal trunk wall, rounded vagina, and unusually dorsal gonopore. The hosts and geographical distribution of R. trachuri suggest a northern linkage of infections between the Asian and American Pacific populations across the Bering Sea involving salmonid fishes and a southern linkage through the Indian Ocean involving Carangid fishes. Other hosts involved in the cycling and distribution of infections are also discussed with some definitive hosts also serving as paratenic hosts. CONCLUSIONS: This is the first complete description about R. trachuri and the first comprehensive accounting of its worldwide distribution in 19 species of marine fish in seven families. Considerable intraspecific variability related to geographical restrictions, intermediate and definitive host specificity and distribution, and host feeding behavior was documented.
Subject(s)
Acanthocephala/anatomy & histology , Acanthocephala/classification , Fish Diseases/parasitology , Host Specificity , Perciformes/parasitology , Animals , Beloniformes/parasitology , California , Female , Geography , Helminthiasis, Animal , Indian Ocean , Male , Oceans and Seas , Parasitic Diseases, Animal/parasitology , Salmonidae/parasitology , VietnamABSTRACT
Diphyllobothriosis is a reemerging zoonotic disease because of global trade and increased popularity of eating raw fish. We present molecular evidence of host switching of a human-infecting broad fish tapeworm, Dibothriocephalus latus, and use of salmonids as intermediate or paratenic hosts and thus a source of human infection in South America.