Water Crayfish Research Articles

English

Abstract The Big Water Crayfish, Cambarus robustus, is native to several eastern U.S. states and Ontario, Canada. Cambarus robustus possesses several traits that make it a potential surrogate for federally listed species, such as the Big Sandy Crayfish, Cambarus callainus, and the Guyandotte River Crayfish, Cambarus veteranus. Basic husbandry information, like optimal temperature, and shelter requirements, have yet to be investigated for most Cambarus species. Therefore, to create a protocol for shelter requirements and preferences for federally listed Cambarus species, we conducted a shelter preference study with C. robustus. Thirty-one crayfish were placed in two treatments where opportunities to burrow underneath natural shelters, clear acrylic shelters, or tinted acrylic shelters were presented. Clear and tinted acrylic shelters are beneficial for investigators as they allow for monitoring of behavior and health without disrupting the crayfish. Each of the two trials lasted 24 hours and were video recorded to monitor behavior and shelter use. Our results suggest that C. robustus will use all shelter types, although natural shelters were occupied more frequently than acrylic shelters. Sex and size had minimal or no influence on shelter use. Future studies should continue to investigate husbandry and rearing techniques for Cambarus spp. and other species where propagation and head-starting efforts will commence.

Recycling crayfish shell and waste activated sludge as biochar to in-situ enhance antibiotics removal from wastewater: Linking structure properties and reaction kinetics

Aquaculture water represents a substantial source of antibiotics in the environment, thereby implicating potential hazards to human health and ecological stability. Additionally, the cultivation of crayfish in such water exacerbates concerns regarding the management of shell waste. In this investigation, crayfish shells and waste activated sludge were repurposed as biochar for the in-situ mitigation of antibiotics elimination from aquaculture wastewater. Compared to crayfish biochar (C-BC) solely from crayfish shell, crayfish sludge biochar (CS-BC) significantly enhances the adsorption of typical antibiotics like tetracycline and ciprofloxacin by 50.3–77.1 %. Findings from kinetic and isotherm experiments suggest that antibiotics adsorption mainly involves physical pore filling, but sludge introduction shifts CS-BC towards chemical adsorption. Further analysis reveals that sludge introduction reduces biochar pore size, boosts specific surface area, and offers more active adsorption sites. Additionally, hydrogen bonding on hydroxyl groups and increased oxygen-containing functional groups enhanced antibiotic adsorption onto CS-BC surfaces. This research presents a promising strategy for addressing antibiotic pollution in aquatic environments while also improving the utilization of organic solid waste resources.

Cardiac Activity of <i>Pontastacus leptodactylus</i> Esch. (Decapoda) under Prolonged Exposure to High Salinity: on the Possibility of Using Freshwater Crayfish in Testing of Brackish Waters

In this study, we analyzed the characteristics of the cardiac activity of crayfish during long-term keeping of animals in an environment with high salinity (6.5‰) in order to find out the fundamental possibility of using them as bioindicators in bioelectronic systems for monitoring the quality of marine coastal waters under high anthropogenic load. Similar salinity values were noted for many bays of the Baltic Sea sub-regions, for example, the Tallinn and Bothnian bays, which are characterized by intense anthropogenic load. It was found that an increase in water salinity from 0 to 6.5‰ caused an initial short-term increase in heart rate (HR) by 30%. It has been shown that crayfish can not only successfully survive for 1 month in high salinity water, but also change the characteristics of cardiac activity to a small extent. Some features were revealed in crayfish in water with altered salinity. During exposure to saline solution, crayfish showed a clear diurnal rhythm of cardiac activity. The rhythmicity of the heart rate disappeared a few days before the molt in both fresh and salt water. The study made it possible to draw a conclusion about the possibility of using freshwater crayfish in bioelectronic systems for continuous monitoring of the functional state of representatives of the local biota and for identifying the biological effects of pollutants in both fresh and brackish water.

Shellfish as Biosensors in Online Monitoring of Aquatic Ecosystems: A Review of Russian Studies

The use of biological objects in monitoring the state of the environment and the changes caused by the impact of environmental pollution on marine and fresh waters is a promising tool due to a lower cost in comparison to traditional monitoring and the ability to receive immediate information about the ecosystem status. In this review, we summarize the biological information about shellfish biomonitors and the results of studies focused on the development and use of the bioindicator species in early warning systems in Russia. Since the mid-1980s, Russian specialists have developed online biomonitoring systems; as in the rest of world, there are two main approaches that are currently applied to study the physiological status of potential biosensor shellfish species and to monitor freshwater and marine systems: valvometry (registration of gaping activity in bivalve mollusks) and photoplethysmography (registration of cardiac activity in mollusks and crustaceans). Valve movement responses to stressors such as abnormal conditions and pollutants include the closure of shell valves for a long period, decrease in the average distance between valves, rapid shell opening, and higher closing frequency. Cardiac activity reactions of shellfish to stress factors include rapid increases in heart rate and stress index, higher variability in heart rate than under normal conditions, and longer periods required for heart rate recovery after stress. The most common bioindicators used to monitor environmental disturbances in marine ecosystems are blue mussels, Iceland scallops, and red king crabs in cold-water habitats and Black Sea mussels in warmer waters as well as freshwater mussels and crayfish in fresh waters.

Determination of Soil Cadmium Safety Thresholds for Food Production in a Rice-Crayfish Coculture System.

Previous studies have mainly focused on cadmium (Cd) contamination in conventional rice monocultures, and no research on rice-crayfish coculture has been reported. In this study, a Cd-contaminated (0-30 mg kg-1) rice-crayfish co-culture system was established by adding exogenous Cd. The results showed that the Cd concentration in each tissue of rice and each organ of crayfish increased with increasing soil Cd concentration. Specifically, the Cd concentration in each rice tissue was as follows: root > stem > leaf ≈ panicle > grain > brown rice, and the jointing and heading stages were critical periods for the rapid enrichment of Cd in the aboveground tissues of rice. The Cd concentration in each organ of crayfish was as follows: hepatopancreas > gut > gill ≈ exoskeleton > abdominal muscle. Cd was gradually enriched in the abdominal muscle after 30 days of coculture between crayfish and rice. Pearson's correlation analysis showed that the soil's total Cd concentration, available Cd concentration, and water Cd concentration were positively correlated with Cd content in various tissues of rice and various organs of crayfish, whereas EC and TDS in water were markedly related to rice stems, leaves, stalks, and small crayfish. According to the maximum limit of Cd in grain (0.2 mg kg-1) and crustacean aquatic products (0.5 mg kg-1) in China, the safe threshold of soil Cd for rice and crayfish under the rice-crayfish coculture system is 3.67 and 14.62 mg kg-1, respectively. Therefore, when the soil Cd concentration in the rice-crayfish coculture system exceeds 3.67 mg kg-1, the safety risk to humans through the consumption of food from this coculture system will increase. This study provides a theoretical basis for safe food production in a rice-crayfish coculture system using the established Cd pollution model.

Oxygen consumption in relation to current velocity and morphology in the highly invasive crayfish Procambarus clarkii

The red swamp crayfish (Procambarus clarkii) is the most widely spread freshwater crayfish worldwide. Competing physiological traits can influence invasion success in any given environment by limiting the available scope for aerobically demanding activities. While high flows have been associated with reduced crayfish movement upstream, the effects of flow alteration on their metabolic demands have been largely overlooked. In this study, we estimated routine metabolic rate (RMR) at rest and oxygen consumption rates of crayfish under different current velocities in a flume respirometer, while maximum metabolic rate (MMR) was determined using the exhaustive chase protocol. We also measured some morphometric variables in males and females of crayfish. Oxygen uptake substantially increased with crayfish size and current velocity due to increased energy expenditure to overcome drag and hold a stationary position. Sexual dimorphism in morphological traits did not lead to sexual differences in oxygen uptake. Moreover, we found that individuals operated close to their maximum aerobic capacity at elevated current velocities (≥ 25 cm s−1). This suggested that the high flow-driven energetic demand may compromise the energy available for reproduction, growth and dispersal, thereby affecting overall fitness. These metabolic constraints could partly explain the failed invasions of invasive crayfish in fast-flowing waters.

Interleukin enhancer binding factor 2 (IEBF 2) was involved in the regulation of the antibacterial immune reactions in fresh water crayfish, Procambarus clarkii

Although interleukin and interleukin analogues which play important immunomodulatory roles in mammals have not yet been reported in invertebrates, interleukin enhancer binding factor (IEBF) which acts as a transcription factor has been recently studied in several crustaceans and it may be involved in innate immune defence against pathogens. In this study, an IEBF 2 homologue was identified in the fresh water crayfish, Procambarus clarkii. The significantly changed expression levels of Pc-iebf 2 after bacterial challenge revealed the possibility of its participation in defence against bacterial infection. The results of an RNAi assay showed that the crayfish survival rate was obviously decreased after dsIEBF 2 injection, compared with the control groups. And S. aureus proliferation was obviously enhanced at 24 and 48 h post bacterial injection, when Pc-iebf 2 was knocked down. The possible molecular mechanisms for the innate immune regulation functions of Pc-IEBF 2 were also investigated. We speculated that Pc-IEBF 2 plays an important role in defending against bacterial infection in crayfish. It could regulate some innate immune responses by affecting the Toll signalling pathway, melanisation, and cell apoptosis.

Molecular characterization and expression analysis of tumor necrosis factor receptor-associated factor 6 (traf6) like gene involved in antibacterial innate immune of fresh water crayfish, Procambarus clarkii

In invertebrates, innate immunity was the crucial defending pattern against pathogenic microorganisms. For the past few years, Toll or Toll like receptors (TLRs) signaling pathway was studied extensively in crustaceans. Among the components of Toll or Toll like receptors (TLRs) signaling pathway, tumor necrosis factor receptor-associated factor 6 (TRAF6) acted as an important cytoplasmic adaptor, which was conserved from Drosophila to human. In this study, a new traf6 like gene was cloned from hepatopancreas of P. clarkii. After challenged respectively by S. aureus or E. ictaluri, the expression profiles were studied. And the results showed that the mRNA transcript of Pc-traf6 like gene was up-regulated significantly in the hemocytes, hepatopancreas, gills, and intestine of crayfish. After Pc-traf6 like gene was knocked down, the expression levels of transcription factor (Dorsal) and some crucial immunity effectors (ALF 3, Lysozyme 1, Lectin 1, and Crustin 2) in TLRs signaling pathway were dramatically suppressed. Simultaneously, the survival rate of crayfish challenged respectively by S. aureus or E. ictaluri was significantly decreased in RNAi assay. All these results indicated that Pc-traf6 like gene played an important role in regulating the expression of downstream effectors in the TLRs signaling pathway of crayfish.

A new antimicrobial peptide isoform, Pc-crustin 4 involved in antibacterial innate immune response in fresh water crayfish, Procambarus clarkii

The main advantage of antimicrobial peptides (AMPs) used as the effectors in the innate immunity system of invertebrates is that the high specificity is not indispensable. And they play important roles in the systemic defenses against microbial invasion. In this study, a new full-length cDNA of the crustins molecule was identified in red swamp crayfish, P. clarkii (named Pc-crustin 4). The ORF of Pc-crustin 4 contained 369 bp which encoded a protein of 122 amino acids, with a 20-amino-acid signal peptide sequence. On the base of the classification method established by Smith et al., Pc-crustin 4 belonged to Type Ⅰ crustin molecule. The Pc-crustin 4 transcripts were expressed in hemocytes at relatively high level, and relatively low level in hepatopancreas, gills, and intestine in normal crayfish. After respectively challenged with S. aureus or E. ictaluri, the expression levels of Pc-crustin 4 showed up-regulation trends at different degrees in the hemocytes, hepatopancreas, gills, and intestine tissues. Besides, the results of liquid antibacterial assay showed that rPc-crustin 4 inhibited obviously the growth of S. aureus and E. ictaluri. The results of bacteria binding assay showed that rPc-crustin 4 could bind strongly to S. aureus and E. ictaluri. Finally, RNAi assay was performed to study the immunity roles of Pc-crustin 4 in crayfish in vivo. Taken together, Pc-crustin 4 is an important immunity effector molecule, which plays crucial roles in defending against bacterial infection in crayfish.

Effects of long-term starvation on health indices, gut microbiota and innate immune response of fresh water crayfish, marron (Cherax cainii, Austin 2002)

Present study aimed to investigate the physiological and molecular response of 28-days starved marron (Cherax cainii), an economically important freshwater crayfish species. Thirty two marron were randomly distributed into two distinct groups in quadruplicated tanks with a density of 4 marron per tank. The feeding- group of marron was fed the marron basal diet on every day while the starved- group was deprived of feed for four weeks. The results showed a significant (P < .05) reduction in protein, energy and fat contents in the tail muscle of marron due to starvation. The microbiome data showed significant modulation of bacterial abundance at both genus and species level in post-starved marron where core microbiota was replaced by Vibrio. The predicted KEGG metabolic pathway based on 16S rRNA data showed a notable shifting of biosynthesis capability towards nutrients stress response activity in starved marron. Significant impact of starvation on the relative expression level of immune genes was observed in starved marron where pro and anti-inflammatory cytokine genes were significantly down-regulated in fourth weeks. This study provides an insights into the immune response and health of marron exposed to starvation under farming conditions.

Marked variations in gut microbiota and some innate immune responses of fresh water crayfish, marron (Cherax cainii, Austin 2002) fed dietary supplementation of Clostridium butyricum.

This study aimed to investigate the effects of Clostridium butyricum as a dietary probiotic supplement in fishmeal based diet on growth, gut microbiota and immune performance of marron (Cherax cainii). Marron were randomly distributed into two different treatment groups, control and probiotic fed group. After 42 days of feeding trial, the results revealed a significant (P < 0.05) increase in growth due to increase in number of moults in marron fed probiotics. The probiotic diet also significantly enhanced the total haemocyte counts (THC), lysozyme activity in the haemolymph and protein content of the tail muscle in marron. Compared to control, the 16S rRNA sequences data demonstrated an enrichment of bacterial diversity in the probiotic fed marron where significant increase of Clostridium abundance was observed. The abundance for crayfish pathogen Vibrio and Aeromonas were found to be significantly reduced post feeding with probiotic diet. Predicted metabolic pathway revealed an increased activity for the metabolism and absorption of carbohydrate, degradation of amino acid, fatty acid and toxic compounds, and biosynthesis of secondary metabolites. C. butyricum supplementation also significantly modulated the expression level of immune-responsive genes of marron post challenged with Vibrio mimicus. The overall results suggest that C. butyricum could be used as dietary probiotic supplement in marron aquaculture.

Prospects for the cultivation of Australian red claw crayfish Cherax quadricarinatus on warm waters of energy facilities

River crayfish - a delicious food product. On the caloric content (72kcal/100g), the content of fats (2.83%), protein (17.13%) and vitamins of group B (thiamine, riboflavin, etc.), crayfish are not inferior to freshwater fish, and by a number of parameters exceed them. Meat of crayfish is rich in sulfur, phosphorus, iron, cobalt, magnesium, fluorine, potassium, selenium, chromium, calcium and vitamins of group B (B12, B6, B2, B1, B9,), C, E, K, PP and D. There is practically no cholesterol in it, but there are a lot of organic acids. A promising target of cultivation, both in Russia and abroad, is currently the Australian red-cheeked crayfish Cherax quadricarinatus. It is cultivated in such countries as: China, Brazil, Ecuador, America, and others. Currently, in spite of the presence of active crayfish farms in Russia, the biotechnology of growing Cherax quadricarinatus is not sufficiently developed. The main advantages of Cherax quadricarinatus over crayfish that live in our region (Astacus leptodactylus, Astacus astacus, etc.) are: high growth rate, tolerance to water quality, lack of pelagic larva stage. It is advisable to use cooler reservoirs of energy objects for growing valuable warm water aquaculture objects, since the water temperature of these reservoirs is higher than the natural. Energy can contribute to the development of warm water crayfish farming both in the Republic of Tatarstan and in Russia as a whole. Due to the excessive heat that enters the natural reservoirs from energy facilities, an excellent opportunity appears in the absence of the cost of expensive equipment, to grow valuable products. According to expert estimates, the cultivation of crayfish is 5-6 times more profitable than fish.

A Reassessment of the Crayfishes of Pennsylvania's Lake Erie Basin with an Emphasis on Zoogeography, Taxonomy, and Conservation.

An investigation is currently underway to reassess the crayfishes of the Lake Erie basin in northwestern Pennsylvania. A total of 54 stream sites were sampled, with a majority of the streams in the basin sampled at least once. Preliminary data have revealed that the most common crayfish species are Cambarus robustus (Big Water Crayfish), Faxonius propinquus (Northern Clearwater Crayfish), and Cambarus carinirostris (Rock Crayfish) respectively. Faxonius obscurus (Allegheny Crayfish) was discovered in one tributary to Elk Creek and a tributary to Lake Erie, not supporting prior belief that F. obscurus was forcing F. propinquus into smaller tributaries. Three additional species, Faxonius immunis (Calico Crayfish), Creaserinus fodiens (Digger Crayfish), and Cambarus spp. were collected via trapping. Procambarus acutus (White River Crayfish), an invasive crayfish species, was also collected via trapping. The presence of such a diverse crayfish fauna is likely due to the postglacial movement via stream and wetland migrations. The Lake Erie basin represents a range overlap for northern and southern crayfish species, and is a unique location within Pennsylvania’s watersheds.

Clinical features of Haff disease and myositis after the consumption of boiled brackish water crayfish: a retrospective study of 96 cases at a single centre.

The present study describes the difference in clinical features between the patients with Haff disease and crayfish-related myositis (CRM) after crayfish consumption. This was a single-centre, retrospective analysis at the Emergency Department of the Drum Tower Hospital of Nanjing University School of Medicine from July to August of 2016. The baseline information came from the Electronic Medical Record System at the institution. Totally 96 patients were included, of whom 52 patients were confirmed to have Haff disease and 44 patients were CRM. The illness predominately occurs in summer and most of them (55/96) are female. The primary clinical features are myalgia, muscle allodynia and back and body pain. Statistical differences in the baseline CK, CK-MB, myoglobin, and the WBC count exist between the Haff disease and CRM groups (P < 0.05). The serum levels of CK and CK-MB increase in the second (a median time 29.2 ± 7.4h) or third day (a median time 54.8 ± 9.3h) of disease course, and then rapidly decreased to normal levels, while the levels of myoglobin peak at the admission (a median time 7.7 ± 6.4h) and became normal after admission. There were no fatalities or complications during this study. All 96 patients recovered in a week. Of them, 75 were followed-up within 1month and none had recurrence. The Haff disease and CRM after boiled crayfish consumption reflect a different severity of muscle injury, and reveal similar clinical characteristics and most of the laboratory values. The overall prognosis of both is good.

Elevated water temperature impairs gamete production in male narrow-clawed crayfish Pontastacus leptodactylus (Eschscholtz, 1823)

Water temperature is one of the major environmental factors affecting the reproductive output of freshwater crayfish. The reproduction of freshwater crayfish only occurs in a limited water temperature range and minor changes in water temperature could have negative impacts on this biological process. Therefore, understanding the potential effects of temperature on the reproductive output of crayfish is important from both an ecological and aquaculture point of view. Spermatozoal production, hepatosomatic index (HSI), gonado-somatic index (GSI), testicular index (TI), and vas deferens index (VDI) were measured in Pontastacus leptodactylus maintained at 7.5, 11, and 19 °C during the reproductive season. It was found that the highest temperature significantly degrades the production of spermatozoa and VDI when compared to the crayfish maintained at lower temperatures (P &lt; 0.05). On the other hand, water temperature did not significantly affect the values of HSI, GSI, and TI (P &gt; 0.05). Furthermore, the highest temperature caused a negative impact on the vas deferens characterized by a softer and more adhesive texture. In conclusion, this study demonstrated that elevated water temperature has a negative impact on gamete production of male P. leptodactylus, as a cold water crayfish species, and may subsequently affect the whole reproduction process.

Exclusion of fish and invertebrates from benthic patches of artificial aquatic environments across water conductivity levels using high-frequency (10 Hz) pulses and adjustable electrical settings

Livestock fence chargers are often used to generate pulsed electrical fields in freshwater environments to exclude fish and invertebrates from benthic patches so that their ecological function can be investigated. Such devices appear to be effective, but the precise characteristics of the electrical fields they generate and specific settings needed to exclude organisms across water conductivity levels have not been described. We present an electrical engineering and experimental framework to predict and evaluate the effectiveness of a modified device at different combinations of electrical settings and water conductivities. We avoided toxic materials and considered safety issues. We conducted laboratory experiments to identify the electrical fields with a 10-Hz pulse frequency needed to exclude adult Fathead Minnows (Pimephales promelas) and crayfish (Procambarus clarkii) from electrical exclosures across a range of water conductivities (13–800 µS/cm). Fish and crayfish in waters of low conductivity (≤50 µS/cm) were excluded from exclosures at ≥200 V of electric potential. In water of higher conductivity (≥250 µS/cm), similar settings caused consumer immobilization. Electrical pulse durations of 150 µs were more effective than 50-µs pulse durations at excluding organisms. Further refinement toward standardized methods requires analogous experimentation in the field, but our findings emphasize the importance of comprehensively considering electrical fields (voltage, pulse frequency and duration), water conductivity, and electrode configuration a priori when using these devices to optimize designs.

New Records of Entocytherid Ostracods from New York and New Jersey

Abstract Ostracods of the family Entocytheridae are obligate ectosymbionts, primarily of crayfishes. Although the distribution and diversity of crayfishes is well known in the northeastern US, little is known about entocytherids in this region. In this study, we examined 5 species of crayfishes—Procambarus acutus (White River Crayfish), Orconectes limosus (Spinycheek Crayfish), Orconectes propinquus (Northern Clearwater Crayfish), Cambarus bartonii (Common Crayfish), and Cambarus robustus (Big Water Crayfish)—from 3 counties in New York (Saratoga, Orange, and Tompkins) and 8 counties in New Jersey (Essex, Sussex, Atlantic, Burlington, Camden, Cumberland, Gloucester, and Ocean). We recovered 2 species of entocytherid ostracods: Donnaldsoncythere cayugaensis and Donnaldsoncythere donnaldsonensis. Records from our study expand the known range of D. cayuagensis and fill in gaps in the known range of D. donnaldsonensis.

Survey on the parasites infested crayfish Procambarus clarkii, Girard,1852 (Crustacea, Cambaridae) in Egypt.

A parasitological survey on 1474 fresh water crayfish Procambarus clarkii was carried out during the period from January 2013 till May 2014 from different canals at Sharkia, Dakahlia and Kafr El-Sheikh Provinces in Egypt. Out of the examined crayfish , 8 were found to be infected with ectoparasitic protozoan Epistylis cambari on the gill filaments with percentage of infection 0.54% . Infection rates were varied between investigated areas, the percentages of infection were 0.21%, 0.57% and 2.7% at Sharkia, Dakahlia and Kafr El- Sheikh provinces respectively. Regarding to the seasonal prevalence of Epistylis cambari in examined crayfishes the peak of infection at Sharkia Province was recorded in summer (3.5%) , while at Dakahlia and Kafr El- Sheikh Provinces was detected in spring (1.13%) and (5.12%) respectively. The present study revealed that 11 out of 1474 (0.88%) were infected by one or more parasitic nematode larvae Strongyloides stercoralis that were observed in hemoceol of crayfish .The percentages of infection were 0.31%, 2.3% and 1.3% at Sharkia, Dakahlia and Kafr El-Sheikh Provinces respectively. Concerning to the seasonal prevalence of nematode larvae in examined crayfish, the peak of infection at Sharkia Province was detected in spring (4.5 %) ,while at Dakahlia Province was in summer (3.2%) and at Kafr El-Sheikh Province was in spring (1.5%). No infection was detected in winter and autumn.

BAX, a novel cell pro-apoptotic protein, involved in hemocytes early antiviral immune response in fresh water crayfish, Procambarus clarkii.

Apoptosis plays an important role in various biological processes and acts as a host defending mechanism by which infected cells are eliminated to restrict the virus propagation scale. Bax is a crucial pro-apoptotic protein, which mediates the release of cytochrome c from mitochondrion to cytosol in mammalian. However, its role in invertebrate is still obscure. Here, a novel pro-apoptotic protein gene was identified from hemocytes of red swamp crayfish. There was a Bcl-2 domain in the C-terminus of Pc-Bax, which possessed 497amino acids residues. And an important transmembrane region existed in the C-terminus of Pc-Bax, which implied that Pc-Bax located in mitochondrial membrane. Besides, Pc-Bax was expressed at a relative high level in hemocytes, and a relative low expression levels in hepatopancreas, gills, and intestine. In hemocytes, Pc-Bax transcript was rapidly up-regulated from 12h to 36h after WSSV infection. And there was the same trend for Pc-Bax protein expression level in hemocytes after WSSV infection. Results of qRT-PCR testing for VP28 gene showed WSSV replication was obviously enhanced after Pc-Bax knockdown. Meantime, hemocytes apoptosis was suppressed in Pc-Bax knockdown crayfish after WSSV injection, compared with the dsGFP injection group and normal group. Taken together, these results revealed that crayfish hemocytes apoptosis scale was enhanced to suppress WSSV replication by up-regulating Bax protein expression level after WSSV infection.

The crayfish plague pathogen can infect freshwater‐inhabiting crabs

Summary The oomycete Aphanomyces astaci is generally considered a parasite specific to freshwater crayfish, and it has become known as the crayfish plague pathogen. Old experimental work that reported transmission of crayfish plague to the Chinese mitten crab Eriocheir sinensis, and the ability of A. astaci to grow in non‐decapod crustaceans, has never been tested properly. We re‐evaluated the host range of A. astaci by screening for the presence of A. astaci in two crab species cohabiting with infected crayfish in fresh waters, as well as in other higher crustaceans from such localities. The animals were tested with species‐specific quantitative PCR, and the pathogen determination was confirmed by sequencing of an amplified fragment of the nuclear internal transcribed spacer. Furthermore, we examined microscopically cuticle samples from presumably infected crab individuals for the presence of A. astaci‐like hyphae and checked for the presence of pathogen DNA in such samples. Screenings of benthopelagic mysids, amphipods and benthic isopods did not suggest infection by A. astaci in non‐decapod crustaceans. In contrast, both studied lake populations of crabs (a native semiterrestrial species Potamon potamios in Turkey, and an invasive catadromous E. sinensis in Sweden) were infected with this parasite according to both molecular and microscopic evidence. Analyses of polymorphic microsatellite loci demonstrated that A. astaci strains in the crabs and in cohabiting crayfish belonged to the same genotype group, suggesting crayfish as the source for crab infection. The potential for A. astaci transmission in the opposite direction, from crabs to crayfish, and potential impact of this pathogen on populations of freshwater crabs require further investigations, because of possible consequences for crayfish and freshwater crab conservation and aquaculture.