Molecular detection of Aphanomyces astaci - An improved species specific qPCR assay.

The parasitic oomycete Aphanomyces astaci is the causative agent of crayfish plague, a devastating disease for European freshwater crayfish. Species specific quantitative real-time PCR (qPCR) can offer rapid detection of the pathogen. However, the well established A. astaci qPCR assay recommended by the World Organization for Animal Health (WOAH) amplifies the recently described Aphanomyces fennicus. Consequently, false-positive results may occur. This calls for the improvement of the established species specific A. astaci qPCR assay in order to avoid amplifying A. fennicus while screening for A. astaci. We developed an improved species specific A. astaci qPCR assay and validated the assay across three laboratories, using established procedures including different qPCR master mixes for each respective laboratory. Genomic DNA from A. astaci, A. fennicus and closely related Aphanomyces spp. was analysed and compared with both the improved and established assay. Additionally, DNA from crayfish tissue and environmental samples were analysed with both assays. The improved assay showed similar sensitivity with the established assay for all sample types, while proving highly specific for A. astaci avoiding amplification of A. fennicus and the other tested Aphanomyces spp. Environmental DNA (eDNA) samples collected at River Lierelva in Norway amplified with the established assay, but not with the improved assay indicating false positive. We were able to sequence a 530 bp fragment of the ITS region from these eDNA samples and the consensus sequence showed 99.9-100 % pairwise identity with A. fennicus and 97.2-98 % pairwise identity with A. astaci, suggesting that the occurrence of A. fennicus is not limited to Finland, where it was first discovered.

Cambaraspora faxoni n. sp. (Microsporidia: Glugeida) from native and invasive crayfish in the USA and a novel host of Cambaraspora floridanus.

Crayfishes are among the most widely introduced freshwater taxa and can have extensive ecological impacts. Knowledge of the parasites crayfish harbor is limited, yet co-invasion of parasites is a significant risk associated with invasions. In this study, we describe a novel microsporidium, Cambaraspora faxoni n. sp. (Glugeida: Tuzetiidae), from two crayfish hosts in the Midwest USA, Faxonius virilis and Faxonius rusticus. We also expand the known host range of Cambaraspora floridanus to include Procambarus spiculifer. Cambaraspora faxoni infects muscle and heart tissue of F. rusticus and develops within a sporophorous vesicle. The mature spore measures 3.22 ± 0.14 µm in length and 1.45 ± 0.13 µm in width, with 8-9 turns of the polar filament. SSU sequencing indicates the isolates from F. virilis and F. rusticus were identical (100%) and 93.49% similar to C. floridanus, supporting the erection of a new species within the Cambaraspora genus. The novel parasite was discovered within the native range of F. rusticus (Ohio, USA) and within a native congeneric (F. virilis) in the invasive range of F. rusticus (Wisconsin, USA). Faxonius virilis is invasive in other regions. This new parasite could have been introduced to Wisconsin with F. rusticus or it may be a generalist species with a broad distribution. In either case, this parasite infects two crayfish species that have been widely introduced to new drainages throughout North America and could have future effects on invasion dynamics or impacts.

Crayfish co-introduced symbiotic ostracod found on native crab in Japan: The first record of epibiont ostracod found a new host.

Ankylocythere sinuosa (Rioja, 1942), a symbiotic ostracod native to North America, was found from the Japanese mitten crab Eriocheir japonica (De Haan, 1835), a species native to Japan, collected from a pond in Shizuoka City, Shizuoka Prefecture, central Japan. Introduced North American crayfish Procambarus clarkii (Girard, 1852), which is a host of A. sinuosa in their native range, inhabits ponds sympatrically with Japanese mitten crabs, and it is thought that the ostracods transferred from the exotic crayfish to the native crabs. In recent years, along with the artificial transportation of crayfish around the world, their symbiotic ostracods also have been found on the body surfaces of exotic crayfish in Europe and Japan. However, no studies have confirmed the infestation of exotic ostracods on native crustaceans in the field. A wide range of developmental stages of A. sinuosa from juveniles to adults were found in Japanese mitten crabs, and mating individuals were also found. This strongly suggests that they can reproduce on the body surface of Japanese mitten crabs. In the future, it will be necessary to strengthen measures against alien species to prevent these exotic symbionts from infestating native ecosystems, and we also need to investigate the exact impact of this symbiont on Japanese mitten crabs.

First Record of Psorospermium sp. (Class: Mesomycetozoea) in Northern Clearwater crayfish Faxonius propinquus Girard 1852 (Decapoda: Cambaridae) from Michigan, U.S.A.

Psorospermium cf. haeckeli Hilgendorf 1883 is a unicellular, eukaryotic protozoan within the class Mesomycetozoea, phylogenetically situated near the animal-fungal divergence(Cavalier-Smith 1998; Ragan et al. 1998). Although only one species has been identified, there have been four morphotypes described in 17 species of crayfish from the Holarctic, Neotropical, and Australasian regions (Herbert 1987; Henttonen et al. 1992, 1994; Rug Vogt 1994). However, molecular analyses of the internal transcribed spacer DNA suggest morphotypes may represent distinct species (Bangyeekhun et al. 2001).

A Comprehensive Review on Crustaceans' Immune System With a Focus on Freshwater Crayfish in Relation to Crayfish Plague Disease.

Freshwater crayfish immunity has received great attention due to the need for urgent conservation. This concern has increased the understanding of the cellular and humoral defense systems, although the regulatory mechanisms involved in these processes need updating. There are, however, aspects of the immune response that require clarification and integration. The particular issues addressed in this review include an overall description of the oomycete Aphanomyces astaci, the causative agent of the pandemic plague disease, which affects freshwater crayfish, and an overview of crustaceans' immunity with a focus on freshwater crayfish. It includes a classification system of hemocyte sub-types, the molecular factors involved in hematopoiesis and the differential role of the hemocyte subpopulations in cell-mediated responses, including hemocyte infiltration, inflammation, encapsulation and the link with the extracellular trap cell death pathway (ETosis). In addition, other topics discussed include the identity and functions of hyaline cells, the generation of neoplasia, and the emerging topic of the role of sessile hemocytes in peripheral immunity. Finally, attention is paid to the molecular execution of the immune response, from recognition by the pattern recognition receptors (PRRs), the role of the signaling network in propagating and maintaining the immune signals, to the effector elements such as the putative function of the Down syndrome adhesion molecules (Dscam) in innate immune memory.

Patterns of infection in a native and an invasive crayfish across the UK.

Invasive crayfish and the introduction of non-native diseases pose a significant risk for the conservation of endangered, white-clawed crayfish (Austropotamobius pallipes). Continued pollution of waterways is also of concern for native species and may be linked with crayfish disease dynamics. We explore whether crayfish species or environmental quality are predictors of infection presence and prevalence in native A. pallipes and invasive signal crayfish (Pacifastacus leniusculus). We use a seven-year dataset of histology records, and a field survey comparing the presence and prevalence of infectious agents in three isolated A. pallipes populations; three isolated P. leniusculus populations, and three populations where the two species had overlapped in the past. We note a lower diversity of parasites (Simpson's Index) in P. leniusculus ('Pacifastacus leniusculus Bacilliform Virus' - PlBV) (n = 1 parasite) relative to native A. pallipes (n = 4 parasites), which host Thelohania contejeani, 'Austropotamobius pallipes bacilliform virus' (ApBV), Psorospermium haeckeli and Branchiobdella astaci, at the sites studied. The infectious group present in both species was an intranuclear bacilliform virus of the hepatopancreas. The prevalence of A. astaci in A. pallipes populations was higher in more polluted water bodies, which may reflect an effect of water quality, or may be due to increased chance of transmission from nearby P. leniusculus, a species commonly found in poor quality habitats.

Crayfish plague in Czechia: Outbreaks from novel sources and testing for chronic infections.

The crayfish plague pathogen Aphanomyces astaci, which is among the most studied pathogens of aquatic invertebrates, co-evolved with North American crayfish species but threatens crayfish on other continents. The pathogen causes mass mortalities, particularly in Europe. In this study we document 12 crayfish plague outbreaks that occurred from 2014 to 2019 in Czechia and, by using available molecular techniques (microsatellite and mtDNA markers), we reveal the A. astaci genotypes involved. Our results provide the first evidence of strains from genotype group D, originally associated with the host Procambarus clarkii, causing Astacus astacus and Austropotamobius torrentium mass mortalities in Czechia. Moreover, mtDNA sequencing confirmed two distinct haplotypes of the D haplogroup, indicating two independent sources of infection, presumably originating from ornamental crayfish in the pet trade or spreading from crayfish established in neighbouring countries. Genotype group A was recorded in two As. astacus mortalities, and genotype group E, associated with Faxonius limosus, in two Au. torrentium and three As. astacus mortalities. Microsatellite genotyping also reidentified the unusual genotype SSR-Up in two As. astacus outbreaks, ten years after its first documented occurrence. In addition, we tested healthy-appearing indigenous crayfish from 25 localities for potential chronic infections. No traces of A. astaci DNA were detected; chronic infections in European crayfish species thus do not seem a pervasive phenomenon in Czechia. However, their role as A. astaci latent reservoirs, especially in Pontastacus leptodactylus populations introduced to the country since the late 19th century, cannot be excluded.

Non-destructive method for detecting Aphanomyces astaci, the causative agent of crayfish plague, on the individual level.

The pathogenic oomycete Aphanomyces astaci, transmitted mainly by invasive North American crayfish, causes the crayfish plague, a disease mostly lethal for native European crayfish. Due to its decimating effects on native crayfish populations in the last century, A. astaci has been listed among the 100 worst invasive species. Importantly, detecting the pathogen in endangered native crayfish populations before a disease outbreak would provide a starting point in the development of effective control measures. However, current A. astaci-detection protocols either rely on degradation-prone eDNA isolated from large volumes of water or, if focused on individual animals, include killing the crayfish. We developed a non-destructive method that detects A. astaci DNA in the microbial biofilm associated with the cuticle of individual crayfish, without the need for destructive sampling. Efficiency of the new method was confirmed by PCR and qPCR and the obtained results were congruent with the traditional destructive sampling method. Additionally, we demonstrated the applicability of the method for A. astaci monitoring in natural populations. We propose that the new method should be used in future monitoring of A. astaci presence in endangered European native crayfish individuals as an alternative to eDNA-based monitoring.

The complete life cycle of the unusual apostome Hyalophysa clampi (Ciliophora, Apostomatida), a symbiont of crayfish in Alabama (USA).

Hyalophysa clampi Browning and Landers, 2012 was reexamined to determine all stages in the life cycle of this symbiotic ciliate. The cell feeds as a normal exuviotroph within the exoskeleton of its molted crayfish host but does not encyst following the trophont stage. Trophonts transform into swimming tomont stages, which divide by palintomy over successive divisions, splitting to two cells, separating, and repeating. The divisions cease when the daughter cells attain the size of the infestive tomite stage, which attaches to a new crayfish. This unique life cycle is most similar to the European hermit crab symbiont Polyspira delagei, which forms chains of daughter cells during division. Scanning electron microscopy confirmed the unusual presence of two contractile vacuoles in H. clampi, unique among the Apostomatida, and provided ultrastructural details to better understand light microscopy silver staining. The genus diagnosis for Hyalophysa is modified herein to accommodate this new life cycle.

The signal crayfish (Pacifastacus leniusculus) in Lake Tahoe (USA) hosts multiple Aphanomyces species.

The genus Aphanomyces (Oomycetes) comprises approximately 50 known species of water molds in three lineages. One of the most notorious is Aphanomyces astaci, the causative agent of crayfish plague. In this study, fresh isolates of Aphanomyces were collected from 20 live specimens of the signal crayfish Pacifastacus leniusculus (Dana, 1852) from Lake Tahoe, California, providing 35 axenic cultures of A. astaci as well as two apparently undescribed Aphanomyces spp. isolates. Based on the results of ITS-, chitinase-, mitochondrial rnnS- and rnnL-sequences and microsatellite markers combined, the Lake Tahoe A. astaci isolates were identical to isolates of A. astaci B-haplogroup commonly detected in Europe, and infection experiments confirmed their high virulence towards noble crayfish. One of the two undescribed Aphanomyces spp. isolates was highly similar to an Aphanomyces lineage detected previously in crustacean zooplankton (Daphnia) in Central Europe, while the other was distinct and most closely related (ITS sequence similarity of 93%) to either A. astaci or to Aphanomyces fennicus isolated recently from Astacus astacus in Finland. Neither of the two Aphanomyces spp. isolates caused crayfish mortality under experimental conditions. Our results indicate that the populations of North American signal crayfish can act as carriers of both pathogenic and non-pathogenic Aphanomyces at the same time. Furthermore, considering that a limited number of crayfish individuals from a single location yielded multiple distinct Aphanomyces isolates, our results suggest that substantial species diversity within this genus remains undescribed.

The effect of temperature on bacteria-host interactions in the freshwater crayfish, Pacifastacus leniusculus.

Water temperature is known to affect many aspects of aquatic life including immune responses and susceptibility to diseases. In this context, we studied the effect of temperature on the defense system of the freshwater crayfish Pacifastacus leniusculus. Animals were challenged with two pathogenic Gram-negative bacteria, Aeromonas hydrophila and Pseudomonas gessardii, as well as the bacterial cell wall component lipopolysaccharide (LPS) at two different temperatures, cold (6 °C) and room temperature (22 °C). The immune responses were compared by means of differences in mortality, phagocytosis, bacterial clearance, and the melanization reaction of the hemolymph at these two temperatures. We observed that crayfish survival was higher at cold temperature. The mortality rate was zero at 6 °C following A. hydrophila or LPS injections. Furthermore, the bacteria were completely cleared from crayfish after they had been held at 6 °C for more than 9 days. We also observed a strong melanization reaction of hemolymph at 22 °C when stimulated with LPS, as well as with bacteria. Taken together, our results suggest that the cellular immunity is more effective at low temperature in this cold-adapted animal and pathogens are efficiently removed from the body by mean of phagocytosis.

New genotyping method for the causative agent of crayfish plague (Aphanomyces astaci) based on whole genome data.

The oomycete Aphanomyces astaci causes crayfish plague, the most important disease of European freshwater crayfish species. Presumably introduced into Europe 150 years ago with the import of North American crayfish, A. astaci is highly pathogenic to European crayfish species. Five genotypes (A, B, C, D, and E) have been defined based on random amplified polymorphic DNA analysis (RAPD-PCR) from A. astaci pure cultures. The distinction of genotypes is an essential tool to conduct molecular epidemiological studies on crayfish plague and it has been used to clarify and better understand the history and spread of this disease in Europe. Whereas RAPD-PCR requires DNA from pure culture isolates, the development of genotyping tools that can be applied to DNA extracted from clinical samples allows a much wider application of genotyping studies, including revisiting historic samples. In this study, we present a new approach that adds to currently available methods for genotyping A. astaci strains directly from clinical crayfish samples. Whole-genome sequencing of A. astaci strains representing all currently known genotypes was employed, genomic regions unique to the respective genotype identified, and a PCR-based genotyping assay designed, which focuses on the presence/absence of PCR product after amplification with the genotype-specific primers. Our diagnostic methodology was tested using DNA extracts from pure A. astaci cultures, other Aphanomyces species and additional oomycetes, samples from a recent Italian crayfish plague outbreak and additional historical samples available in the Centre for Environment, Fisheries and Aquaculture Science laboratory. The new markers were reliable for pure culture and clinical samples from a recent outbreak and successfully discriminated genotype A, B, D, and E. The marker for genotype C required an additional sequencing step of the generated PCR product to confirm genotype.

MtDNA allows the sensitive detection and haplotyping of the crayfish plague disease agent Aphanomyces astaci showing clues about its origin and migration.

The oomycete Aphanomyces astaci, the causative agent of crayfish plague, is listed as one of the 100 worst invasive species in the world, destroying the native crayfish populations throughout Eurasia. The aim of this study was to examine the potential of selected mitochondrial (mt) genes to track the diversity of the crayfish plague pathogen A. astaci. Two sets of primers were developed to amplify the mtDNA of ribosomal rnnS and rnnL subunits. We confirmed two main lineages, with four different haplogroups and five haplotypes among 27 studied A. astaci strains. The haplogroups detected were (1) the A-haplogroup with the a-haplotype strains originating from Orconectes sp., Pacifastacus leniusculus and Astacus astacus; (2) the B-haplogroup with the b-haplotype strains originating from the P. leniusculus; (3) the D-haplogroup with the d1 and d2-haplotypes strains originating from Procambarus clarkii; and (4) the E-haplogroup with the e-haplotype strains originating from the Orconectes limosus. The described markers are stable and reliable and the results are easily repeatable in different laboratories. The present method has high applicability as it allows the detection and characterization of the A. astaci haplotype in acute disease outbreaks in the wild, directly from the infected crayfish tissue samples.

Uso de monensina sódica en el cultiva de camarón marino Litopenaeus vannamei para el tratamiento de gregarinas en la Cooperativa Fauna Silvestre, Bahía de Jiquilisco: en asocio con Cooperativa Fauna Silvestre / Use of monensin sodium in the cultivation of marine shrimp Litopenaeus vannamei for the treatment of gregarines in Cooperativa Fauna Silvestre, Bahía de Jiquilisco: in association with Cooperativa Fauna Silvestre

Este proyecto estuvo orientado a evaluar el efecto del producto veterinario Monensina Sódica, un anticoccídico utilizado actualmente en el cultivo de camarón marino de la especie Litopennaeus vannamei para el tratamiento de la parasitósis por gregarinas. Durante la investigación se identificó la presencia de gregarinas en los estanques de la Cooperativa Fauna Silvestre; se estableció el porcentaje de la población infectada por gregarinas y se determinó el grado de afectación que presenta el cultivo, información que permitió seleccionar el estanque donde se instalaron tres japas, cada una con una dimensión de tres metros de largo por un metro y medio de ancho y un metro de profundidad; en cada japa se colocaron 100 camarones procedentes del mismo estanque. La aplicación del tratamiento fue por un periodo de 5 días, el cual consistió en evaluar el efecto de dos tratamientos con dosis de 8 y 10 gramos de Monensina Sódica por cada kilogramo de alimento que se suministra por separado a los camarones de las japas uno y dos; el tercer grupo de camarones será la japa testigo en el estudio. Posteriormente se evaluó el crecimiento de los camarones tratados durante un ciclo de cultivo y se comparó con los camarones que no recibieron tratamiento. Las muestras de camarón tomadas en campo fueron trasladadas en bolsas con agua y oxígeno hacia el laboratorio del Centro Regional MEGATEC La Unión, donde fueron procesadas mediante el método de análisis en fresco, método que permitió identificar el grado de infestación del parásito que se aloja en el intestino del camarón. Las muestras se tomaron antes y después de iniciar el tratamiento con Monensina Sódica. Durante la toma y procesamiento de las muestras se contó con la participación de estudiantes del Técnico en Manejo Integrado de Recursos Costero Marinos, con la finalidad de fortalecer sus capacidades mediante la aplicación de procedimiento, para detectar de forma temprana la presencia de Gregarinas en los cultivos de camarón marino.

This project was aimed at evaluating the effect of the veterinary product Monensin Sodium, an anticoccidic currently used in the culture of marine shrimp of the Litopennaeus vannamei species for the treatment of gregarine parasitosis. During the investigation, the presence of gregarines was identified in the ponds of the Cooperativa Fauna Silvestre; The percentage of the population infected by gregarines was established and the degree of affectation presented by the crop was determined, information that allowed selecting the pond where three japas were installed, each one with a dimension of three meters long by one and a half meters of width and a meter deep; 100 shrimp from the same pond were placed in each japa. The application of the treatment was for a period of 5 days, which consisted of evaluating the effect of two treatments with doses of 8 and 10 grams of Monensin sodium for each kilogram of food that is supplied separately to the shrimp of japas one and one. two; the third group of shrimp will be the control japa in the study. Subsequently, the growth of the treated shrimp was evaluated during a culture cycle and compared with the shrimp that did not receive treatment. The shrimp samples taken in the field were transferred in bags with water and oxygen to the laboratory of ITCA-FEPADE MEGATEC La Unión, where they were processed using the fresh analysis method, a method that allowed identifying the degree of infestation of the parasite that is housed in the intestine of the shrimp. The samples were taken before and after starting the treatment with Monensin sodium. During the taking and processing of the samples, students from the Technician in Integrated Management of Coastal Marine Resources participated, in order to strengthen their capacities through the application of a procedure to detect early the presence of Gregarines in crops. of marine shrimp.

Ultrastructural and molecular characterization of Vairimorpha austropotamobii sp. nov. (Microsporidia: Burenellidae) and Thelohania contejeani (Microsporidia: Thelohaniidae), two parasites of the white-clawed crayfish, Austropotamobius pallipes complex (Decapoda: Astacidae).

The microsporidiosis of the endangered white-clawed crayfish Austropotamobius pallipes complex has generally been attributed to only one species, Thelohania contejeani, the agent of porcelain disease. Species identification was mostly assessed by macroscopic examination or microscopic evaluation of muscle samples rather than by molecular or ultrastructural analyses. A survey conducted on A. pallipes complex populations in Northern Italy highlighted the presence of two different microsporidia causing similar muscular lesions, T. contejeani and an undescribed octosporoblastic species Vairimorpha austropotamobii sp. nov. Mature spores and earlier developmental stages of V. austropotamobii sp. nov. were found within striated muscle cells of the thorax, abdomen, and appendages of the crayfish. Only octosporoblastic sporogony within sporophorous vesicles (SPVs) was observed. Diplokaryotic sporonts separated into two uninucleate daughter cells, which gave rise to a rosette-shaped plasmodium, and eight uninucleate spores were produced within the persistent SPV. Ultrastructural features of stages in the octosporoblastic sequence were similar to those described for Vairimorpha necatrix, the type species. Mature spores were pyriform in shape and an average of 3.9 × 2.2 µm in size. The polar filament was coiled 11-14 times, lateral to the posterior vacuole. The small subunit ribosomal RNA gene (SSU rRNA) and the large subunit RNA polymerase II gene (RPB1) of V. austropotamobii sp. nov. were sequenced and compared with other microsporidia. The highest sequence identity of SSU rRNA (99%) and RPB1 (74%) genes was with the amphipod parasite Nosema granulosis and subsequently with V. cheracis, which infects the Australian yabby Cherax destructor. In our work we discuss about the reasons for placing this new species in the genus Vairimorpha. In addition, we provide for T. contejeani a RPB1 gene sequence, supplemental sequences of SSU rRNA gene and ultrastructural details of its sporogony in the host A. pallipes complex.

Incidencia de parásitos y bacterias del genero vibrio en el cultivo de camarón marino desarrollados en cooperativas camaroneras del municipio de Jiquilisco, Departamento de Usulután / Incidence of parasites and bacteria of the vibrio genus in the marine shrimp culture developed in shrimp cooperatives of the municipality of Jiquilisco, Department of Usulután

En El Salvador el 59.3% del camarón marino de la especie Litopenaeus vannamei se produce en la Bahía de Jiquilisco, departamento de Usulután, el cultivo tiene una duración de 60 a 90 días y el peso de cosecha oscila entre 7 y 12 gramos. El bajo crecimiento y las altas mortalidades son problemas que preocupan a este sector productivo. Por esta razón la Escuela Especializada en Ingeniería ITCA-FEPADE a través de la carrera de Gestión Integral de Recursos Marino Costeros, desarrolló una investigación aplicada orientada a identificar la existencia de parásitos y bacterias del género Vibrio en los cultivos de camarón marino que se desarrollan en la zona de Salinas del Potrero y El Zompopero, así como evaluar su incidencia en el cultivo. Con la investigación se detectó la presencia de cinco géneros de parásitos que están presentes en branquias, intestinos y urópodos en el cultivo de camarón marino en grado 1 y 2; ambas categorías se consideran las etapas iniciales de propagación de los parásitos. También se evidenció a través del análisis bacteriológico en el medio de cultivo TCBS, la presencia de bacterias del genero Vibrio en agua, sedimento y camarón.

In El Salvador, 59.3% of the marine shrimp of the Litopenaeus vannamei species is produced in the Bay of Jiquilisco, department of Usulután, the culture lasts from 60 to 90 days and the harvest weight ranges between 7 and 12 grams. Low growth and high mortality are problems that concern this productive sector. For this reason, Escuela Espcializada en Ingeniería ITCA-FEPADE , through the major of Gestión Integral de Recursos Marino Costeros, developed an applied research aimed at identifying the existence of parasites and bacteria of the genus Vibrio in marine shrimp cultures that develop in the area of ​​Salinas del Potrero and El Zompopero, as well as evaluating their impact on the crop. The investigation detected the presence of five types of parasites that are present in gills, intestines and uropods in marine shrimp culture in grade 1 and 2; Both categories are considered the initial stages of parasite spread. The presence of Vibrio bacteria in water, sediment and shrimp is also evidenced through bacteriological analysis in the TCBS culture medium.

Recent Incidence of Paragonimus westermani Metacercariae in Freshwater Crayfish, Cambaroides similis, from Two Enzootic Sites in Jeollanam-do, Korea.

An epidemiological study was performed to know the recent infection status of Paragonimus westermani metacercariae (PwMc) in freshwater crayfish, Cambaroides similis, from 2 streams in Jeollanam-do, Republic of Korea. Crayfish were collected from creeks in Bogil-do (Island), Wando-gun, and in a creek near Daeheung Temple in Haenam-gun. The infection rate of crayfish with PwMc in Bogil-do was 89.8%, and the metacercarial burden was 37 PwMc per the infected crayfish. Crayfish in a creek near Daeheung Temple were larger and twice heavier than those in Bogil-do. Of them, 96.5% were infected with PwMc. An average of 140 metacercariae was found in the infected crayfish, almost quadruple to those of Bogil-do. There was a strong correlation between the number of PwMc and body weight of the crayfish. These results suggest that P. westermani metacercariae are still prevalent in crayfish of the 2 regions in Jeollanam-do, Korea.

The prevalence of Aphanomyces astaci in invasive signal crayfish from the UK and implications for native crayfish conservation.

The crayfish plague agent, Aphanomyces astaci, has spread throughout Europe, causing a significant decline in native European crayfish. The introduction and dissemination of this pathogen is attributed to the spread of invasive North American crayfish, which can act as carriers for A. astaci. As native European crayfish often succumb to infection with A. astaci, determining the prevalence of this pathogen in non-native crayfish is vital to prioritize native crayfish populations for managed translocation. In the current study, 23 populations of invasive signal crayfish (Pacifastacus leniusculus) from the UK were tested for A. astaci presence using quantitative PCR. Altogether, 13 out of 23 (56·5%) populations were found to be infected, and pathogen prevalence within infected sites varied from 3 to 80%. Microsatellite pathogen genotyping revealed that at least one UK signal crayfish population was infected with the A. astaci genotype group B, known to include virulent strains. Based on recent crayfish distribution records and the average rate of signal crayfish population dispersal, we identified one native white-clawed crayfish (Austropotamobius pallipes) population predicted to come into contact with infected signal crayfish within 5 years. This population should be considered as a priority for translocation.

First Introduction of Two Australian Temnocephalan Species into Africa with an Alien Host: Double Trouble.

The redclaw crayfish, Cherax quadricarinatus (Decapoda: Parastacidae), is native to Australia but has been introduced to South Africa as a warm-water aquaculture species. In a South African natural waterbody, examined crayfish had high-intensity infections of 3 temnocephalan species on their body surfaces and within the branchial chambers. Temnocephalans were characterized using light and scanning electron microscopy and identified as Craspedella pedum, Diceratocephala boschmai, and Didymorchis sp. This is the first report of the introduction of Australian temnocephalans, C. pedum and Didymorchis sp., to Africa and expands the known distribution of these species beyond their presumptive native range. The present study also documents a naturalized population of C. quadricarinatus from a natural water body in South Africa, comprising a new geographical locality record.

Parasites alter freshwater communities in mesocosms by modifying invasive crayfish behavior.

Parasites can alter communities by reducing densities of keystone hosts, but few studies have examined how trait-mediated indirect effects of parasites can alter ecological communities. We test how trematode parasites (Microphallus spp.) that affect invasive crayfish (Orconectes rusticus) behavior alter how crayfish impact lake littoral communities. O. rusticus drive community composition in north temperate lakes, and predatory fish can reduce crayfish activity and feeding. In laboratory studies, Microphallus parasites also alter O. rusticus behavior: infected O. rusticus eat fewer macroinvertebrates and are bolder near predatory fish than uninfected individuals. We used a 2 x 2 factorial experiment to test how predatory fish and parasites affect O. rusticus impacts in large mesocosms over 4 weeks. We predicted (1) that when predators were absent, infected crayfish would have lower impacts than uninfected crayfish on macrophytes and macroinvertebrates (as well as reduced growth and higher mortality). However, (2) when predators were present but unable to consume crayfish, infected crayfish would have greater impacts (as well as greater growth and lower mortality) than uninfected crayfish because of increased boldness. Because of its effect on crayfish feeding behavior, we also predicted (3) that infection would alter macrophyte and macroinvertebrate community composition. In contrast to our first hypothesis, we found that infected and uninfected crayfish had similar impacts on lower trophic levels when predators were absent. Across all treatments, infected crayfish were more likely to be outside shelters and had greater growth than uninfected crayfish, suggesting that the reduced feeding observed in short-term experiments does not occur over longer timescales. However, in support of the second hypothesis, when predatory fish were present, infected crayfish ate more macroinvertebrates than did uninfected crayfish, likely due to increased boldness. We also observed a trend for greater macrophyte consumption associated with infection and a trend indicating infection might alter macroinvertebrate community composition. Our results suggest that parasites can alter aquatic communities in mesocosms merely by modifying host behavior.