North American Crayfish Species Research Articles

Comparison of two water sampling approaches for eDNA-based crayfish plague detection

The crayfish plague agent Aphanomyces astaci causes high fatality rates among European crayfish species and is transmitted by semi-immune North American crayfish species via zoospores. Recently environmental DNA (eDNA) techniques have been developed to detect the pathogen directly in water samples.To identify the optimal technique for concentrating spores out of water samples we tested two water filtration methods, namely depth filtration (DF) and dead-end ultrafiltration (DEUF), with subsequent qPCR-based detection of A. astaci spores from the water column in three river systems in Germany.Both eDNA methods were successful in recovering and detecting A. astaci spores from all three lotic water systems and the detection patterns were generally consistent across watercourse and season. Water turbidity negatively affected the A. astaci spore detection with both eDNA methods, with increasing pellet weights for the DEUF method and decreasing water volumes for the DF samples. Although filtering high-volume water samples with the DEUF method led to slightly higher detection rates of A. astaci and seemed to be more sensitive in A. astaci detection, its application is highly laborious and more costly. We therefore propose to use the DF method for large-scale screenings of A. astaci in running waters due to its fast, cost-effective and easy-to-apply sample processing and the very robust quantification results. We are confident that this method might be favored as well for eDNA studies of other organisms.

Resistance to the crayfish plague, Aphanomyces astaci (Oomycota) in the endangered freshwater crayfish species, Austropotamobius pallipes.

The pathogen Aphanomyces astaci Schikora 1906 is responsible for the decline of the native crayfish species of Europe, and their current endangered status. This pathogenic species is native to North America and only colonizes aquatic decapods. The North American crayfish species have a high resistance to this pathogen, while species from other regions are highly susceptible. However, recent field and laboratory observations indicate that there might exist some populations with resistance against this disease. The objective of this study was to test the susceptibility of 8 selected native European crayfish populations of Austropotamobius pallipes Lereboullet 1858 from the Pyrenees. We challenged them against the genome sequenced strain AP03 of A. astaci isolated from a North American red swamp crayfish, Procambarus clarkii Girard 1852, in the Garrotxa Natural Park, Girona. The results showed that there are significant differences (P<0,001) among populations, although most of them show high mortality rates after the zoospore challenge with A. astaci. However, one population from Girona exhibited a 100% survival during a four-month monitoring period under the experimental conditions tested. Histological analyses revealed a high immune reaction in tissues examined, i.e., encapsulation and melanization of hyphae, similar to that found in North American resistant crayfish species. These results represent the first observation of a native European crayfish population showing high resistance towards the most virulent genotype of this pathogen, i.e., genotype Pc. The identification of this population is of key importance for the management of these endangered species, and represents a crucial step forward towards the elucidation of the factors involved in the immune reaction against this devastating pathogen.

Aphanomyces astaci presence in Japan: a threat to the endemic and endangered crayfish species Cambaroides japonicus?

Abstract Spread of the crayfish plague pathogen, Aphanomyces astaci, by North American crayfish species is considered one of the main reasons for substantial declines and local extinctions of native European crayfish populations. Owing to human introductions, several American crayfish species have become established throughout the world, and thus pose a potential threat to indigenous crayfish populations susceptible to crayfish plague. In Japan, two such widespread alien species, Procambarus clarkii and Pacifastacus leniusculus, were introduced for aquaculture purposes in the late 1920s and since then successfully expanded their ranges. Aggressive interactions with alien crayfish along with habitat modifications have been considered primarily responsible for drastic declines in populations of the Japanese endemic crayfish, Cambaroides japonicus, observed in the last few decades. However, the presence of the crayfish plague pathogen, to which Japanese crayfish are susceptible, may be expected, and could contribute to these declines. Only recently, A. astaci has been reported from Taiwan, and to our knowledge no study focusing on its presence outside of the Western Palearctic has been conducted. To fill this gap, 54 P. clarkii and 47 P. leniusculus individuals from five different Japanese locations were screened using molecular methods recommended by the World Organization for Animal Health. Aphanomyces astaci DNA was detected in all studied populations, altogether in 61% and 21% of examined individuals of P. clarkii and P. leniusculus, respectively. The results provide the first evidence of A. astaci presence in Japan and highlight the threat of pathogen transmission to C. japonicus populations. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Effect of experimental exposure to differently virulent Aphanomyces astaci strains on the immune response of the noble crayfish Astacus astacus

European crayfish are sensitive to the crayfish plague pathogen, Aphanomyces astaci, carried by North American crayfish species due to their less effective immune defence mechanisms against this disease. During a controlled infection experiment with a susceptible crayfish species Astacus astacus using three A. astaci strains (representing genotype groups A, B, and E), we investigated variation in their virulence and in crayfish immune defence indicators (haemocyte density, phenoloxidase activity, and production of reactive oxygen species). Experimental crayfish were exposed to two dosages of A. astaci spores (1 and 10sporesmL−1). The intensity and timing of the immune response differed between the strains as well as between the spore concentrations. Stronger and faster change in each immune parameter was observed in crayfish infected with two more virulent strains, indicating a relationship between crayfish immune response and A. astaci virulence. Similarly, the immune response was stronger and was observed earlier for the higher spore concentration. For the first time, the virulence of a strain of the genotype group E (isolated from Orconectes limosus) was experimentally tested. Total mortality was reached after 10days for the two higher spore dosages (10 and 100sporesmL−1), and after 16days for the lowest (1sporemL−1), revealing equally high and rapid mortality as caused by the genotype group B (from Pacifastacus leniusculus). No mortality occurred after infection with genotype group A during 60days of the experimental trial.

A bomb set to drop: parthenogenetic Marmorkrebs for sale in Ireland, a European location without non-indigenous crayfish

Ireland is one of the few locations in Europe where non-indigenous North American crayfish species have not been introduced, and is a refuge for endangered white-clawed crayfish, Austropotamobius pallipes (Lereboullet, 1858). The parthenogenetic crayfish species Marmorkrebs, Procambarus fallax f. virginalis (Hagen, 1870), is sold in the pet trade in Ireland within the recorded range of A. pallipes. Marmorkrebs risk being introduced into Irish waters, where they could threaten A. pallipes populations, particularly as a vector for crayfish plague.

Survey of the crayfish plague pathogen presence in the Netherlands reveals a new Aphanomyces astaci carrier

North American crayfish species as hosts for the crayfish plague pathogen Aphanomyces astaci contribute to the decline of native European crayfish populations. At least six American crayfish species have been reported in the Netherlands but the presence of this pathogenic oomycete with substantial conservational impact has not yet been confirmed in the country. We evaluated A. astaci prevalence in Dutch populations of six alien crustaceans using species-specific quantitative PCR. These included three confirmed crayfish carriers (Orconectes limosus, Pacifastacus leniusculus, Procambarus clarkii), two recently introduced but yet unstudied crayfish (Orconectes cf. virilis, Procambarus cf. acutus), and a catadromous crab Eriocheir sinensis. Moderate levels of infection were observed in some populations of O. limosus and P. leniusculus. Positive results were also obtained for E. sinensis and two Dutch populations of O. cf. virilis. English population of the latter species was also found infected, confirming this taxon as another A. astaci carrier in European waters. In contrast, Dutch P. clarkii seem only sporadically infected, and the pathogen was not yet detected in P. cf. acutus. Our study is the first confirmation of crayfish plague infections in the Netherlands and demonstrates substantial variation in A. astaci prevalence among potential hosts within a single region, a pattern possibly linked to their introduction history and coexistence.

Invasive Chinese mitten crab (Eriocheir sinensis) transmits crayfish plague pathogen (Aphanomyces astaci)

The Chinese mitten crab ( Eriocheir sinensis) is a vector of the fatal crayfish plague pathogen (Aphanomyces astaci). Both species are listed among the worlds 100 worst invasive species. From its origin in China the Chinese mitten crab was introduced to Europe, presumably via ballast water from ships. A. astaci originated in North America and is assumed to have been firstly introduced to Europe through human- mediated transportation of live specimens of North American freshwater crayfish species. While the North American crayfish species are resistant to the pathogen, it causes a fatal disease to native European crayfish species. It was generally assumed that the crayfish plague could only infect freshwater crayfish species. Until recently, the Chinese mitten crab had not been recognised as a host of the pathogen. And no study has yet been carried out to investigate if they also serve as a vector. In this study, transmission experiments are carried out in combination with subsequent species-specific molecular analysis. The results establish that the Chinese mitten crab carry the crayfish plague pathogen and can transmit it to the European noble crayfish (Astacus astacus). The implications of these findings are ecologically alarming, considering the high invasive potential and the catadromous life cycle of Chinese mitten crabs, facilitating the widespread distribution of the pathogen.

Microsatellite markers for direct genotyping of the crayfish plague pathogen Aphanomyces astaci (Oomycetes) from infected host tissues

Aphanomyces astaci is an invasive pathogenic oomycete responsible for the crayfish plague, a disease that has devastated European freshwater crayfish. So far, five genotype groups of this pathogen have been identified by applying random amplified polymorphic DNA analysis on axenic cultures. To allow genotyping of A. astaci in host tissue samples, we have developed co-dominant microsatellite markers for this pathogen, tested them on pure cultures of all genotype groups, and subsequently evaluated their use on tissues of (1) natural A. astaci carriers, i.e., North American crayfish species, and (2) A. astaci-infected indigenous European species from crayfish plague outbreaks. Out of over 200 potential loci containing simple sequence repeat (SSR) motifs identified by 454 pyrosequencing of SSR-enriched library, we tested 25 loci with highest number of repeats, and finally selected nine that allow unambiguous separation of all known RAPD-defined genotype groups of A. astaci from axenic cultures. Using these markers, we were able to characterize A. astaci strains from DNA isolates from infected crayfish tissues when crayfish had a moderate to high agent level according to quantitative PCR analyses. The results support the hypothesis that different North American crayfish hosts carry different genotype groups of the pathogen, and confirm that multiple genotype groups, including the one originally introduced to Europe in the 19th century, cause crayfish plague outbreaks in Central Europe. So far undocumented A. astaci genotype seems to have caused one of the analysed outbreaks from the Czech Republic. The newly developed culture-independent approach allowing direct genotyping of this pathogen in both axenic cultures and mixed genome samples opens new possibilities in studies of crayfish plague pathogen distribution, diversity and epidemiology.

Reproductive Plasticity in Freshwater Invader: From Long-Term Sperm Storage to Parthenogenesis

Orconectes limosus, a North American crayfish species, is one of the most important aquatic invaders in European inland waters. Despite more than 120 years occurrence in Europe and intense research, there are still gaps in knowledge of its life history and ecology. Investigation into O. limosus invasive success requires identifying the mechanisms that enabled them to establish dense and widespread populations from small initial numbers without observable limitation by an introduction bottleneck. In part, O. limosus success may lie in its ability to reproduce by facultative parthenogenesis. Moreover, there are possible other mating scenarios, because of two mating seasons (autumn and spring) in O. limosus. This work investigated the effect of four reproductive scenarios (autumn mating only, spring mating only, autumn and spring mating, and without mating) on the reproductive success of O. limosus. Females successfully reproduced in all tested mating regimes using parthenogenesis as well as log term sperm storage. This reproductive plasticity likely facilitates the overwhelming success of O. limosus spread and establishment in new localities. It can explain the spread of O. limosus from the initial introduction of 90 specimens to most of continental Europe and Great Britain. These conclusions imply a serious threat, not only for autochthonous European astacofauna, but for other aquatic organisms as well as entire ecosystems.

Prevalence of the Crayfish Plague Pathogen Aphanomyces astaci in Populations of the Signal Crayfish Pacifastacus leniusculus in France: Evaluating the Threat to Native Crayfish

Aphanomyces astaci, the crayfish plague pathogen, first appeared in Europe in the mid-19th century and is still responsible for mass mortalities of native European crayfish. The spread of this parasite across the continent is especially facilitated by invasive North American crayfish species that serve as its reservoir. In France, multiple cases of native crayfish mortalities have been suggested to be connected with the presence of the signal crayfish Pacifastacus leniusculus, which is highly abundant in the country. It shares similar habitats as the native white-clawed crayfish Austropotamobius pallipes and, when infected, the signal crayfish might therefore easily transmit the pathogen to the native species. We investigated the prevalence of A. astaci in French signal crayfish populations to evaluate the danger they represent to local populations of native crayfish. Over 500 individuals of Pacifastacus leniusculus from 45 French populations were analysed, plus several additional individuals of other non-indigenous crayfish species Orconectes limosus, O. immunis and Procambarus clarkii. Altogether, 20% of analysed signal crayfish tested positive for Aphanomyces astaci, and the pathogen was detected in more than half of the studied populations. Local prevalence varied significantly, ranging from 0% up to 80%, but wide confidence intervals suggest that the number of populations infected by A. astaci may be even higher than our results show. Analysis of several individuals of other introduced species revealed infections among two of these, O. immunis and P. clarkii. Our results confirm that the widespread signal crayfish serves as a key reservoir of Aphanomyces astaci in France and therefore represents a serious danger to native crayfish species, especially the white-clawed crayfish. The prevalence in other non-indigenous crayfish should also be investigated as they likely contribute to pathogen transmission in the country.

Self-limiting outbreak of crayfish plague in an Austropotamobius pallipes population of a river basin in the Abruzzi region (central Italy)

Crayfish plague, caused by the oomycete Aphanomyces astaci, is a serious disease of European freshwater crayfish and has eliminated entire populations in several European countries. In September 2011, mortality was observed among the Austropotamobius pallipes population of a river basin in the Abruzzi region (central Italy), and A. astaci DNA was detected by PCR in dead crayfish. A systematic survey was carried out to evaluate the spread and the effects of the plague in the river basin. The source of the outbreak remained unknown since North American crayfish species, which frequently act as subclinical carriers of the infection, were not detected in the area. The A. pallipes population disappeared from a river stretch of ~1 km, where A. astaci infection was detected in dead crayfish. However, apparently unaffected crayfish were still present upstream of that area as well as in a tributary that joined the brook in the apparently depopulated stretch. A. astaci infection was not detected in dead individuals collected in the upstream area and tributary. A follow-up visit conducted in the following season showed the presence of A. pallipes in the river stretch hit by the plague. In this outbreak, the spread of the infection could have been limited by a low density of the crayfish population and by the geographic conformation of the river basin, which includes a dense network of small tributaries, characterized by high flow velocity and low water temperature. In this particular setting, crayfish plague outbreaks can remain undetected. This underlines the importance of active monitoring programs aimed at the prompt recognition of both episodes of mortality and the presence of non-indigenous crayfish species.

Crayfish plague agent detected in populations of the invasive North American crayfish Orconectes immunis (Hagen, 1870) in the Rhine River, Germany

Crayfish plague, caused by the parasitic oomycete Aphanomyces astaci, has driven indigenous European crayfish species to regional extinction in many parts of Europe and is among the leading threats to the remaining populations. A. astaci is known to be carried by longestablished invasive crayfish species of North American origin, which are also the main vectors of the plague pathogen. In this study, we examined whether a new invasive crayfish of North American origin, the calico crayfish (Orconectes immunis), also carries A. astaci. Orconectes immunis is a recent invader of the Upper Rhine plain, where it seems to displace its invasive predecessor Orconectes limosus, which is a known carrier of the agent of the crayfish plague. Using real-time PCR, we identified the calico crayfish as the fourth invasive crayfish species to be a carrier of the crayfish plague pathogen in Europe and we confirmed the infection with A. astaci in O. limosus. These findings support the concern that all North American crayfish species in European waters are carriers of the crayfish plague pathogen. Such knowledge should prove useful for conservation efforts, management, legislation, and public education about the spread of crayfish plague and non-indigenous crayfish species.

A Successful Crayfish Invader Is Capable of Facultative Parthenogenesis: A Novel Reproductive Mode in Decapod Crustaceans

Biological invasions are impacting biota worldwide, and explaining why some taxa tend to become invasive is of major scientific interest. North American crayfish species, particularly of the family Cambaridae, are prominent invaders in freshwaters, defying the “tens rule” which states that only a minority of species introduced to new regions become established, and only a minority of those become invasive and pests. So far, success of cambarid invaders has largely been attributed to rapid maturation, high reproductive output, aggressiveness, and tolerance to pollution. We provide experimental evidence that females of one cambarid species particularly widespread in Europe, the spiny-cheek crayfish Orconectes limosus, are capable of facultative parthenogenesis. Such reproductive mode has never before been recognized in decapods, the most diverse crustacean order. As shown by analysis of seven microsatellite loci, crayfish females kept physically separated from males produced genetically homogeneous offspring identical with maternal individuals; this suggests they reproduced by apomixis, unlike those females which mated with males and had a diverse offspring. Further research is needed to clarify what environmental conditions are necessary for a switch to parthenogenesis in O. limosus, and what role it plays in natural crayfish populations. However, if such reproductive plasticity is present in other cambarid crayfish species, it may contribute to the overwhelming invasive success of this group.

Temporal variation in the prevalence of the crayfish plague pathogen,Aphanomyces astaci, in three Czech spiny-cheek crayfish populations

North American crayfish species are natural hosts of the crayfish plague pathogen Aphanomyces astaci . The spiny-cheek crayfish Orconectes limosus , widespread in Central Europe, is the main reservoir of A. astaci in Czech Republic. We tested if there are temporal changes in the prevalence of infected individuals (i.e. , the proportion of individuals in which the pathogen is detected) in spiny-cheek crayfish populations. Crayfish from three populations shown previously to be infected to different extents (high, intermediate and low), were repeatedly sampled in different years (2004–2010) and seasons. The presence of A. astaci in the soft abdominal crayfish cuticle was tested by specific amplification of the pathogen DNA. There was no substantial temporal variation in pathogen prevalence in the highly and very lowly infected populations. However, a significant long-term as well as seasonal decrease was found in the intermediately infected population. This decline could be related to a decrease in population density over the studied years, and to crayfish seasonal moulting, respectively. A reliable estimate of pathogen prevalence in American crayfish populations thus requires repeated monitoring over years, preferably during the same season before the main period of crayfish moulting.

Crayfish plague pathogen in invasive North American crayfish species in Hungary

Journal of Fish DiseasesVolume 33, Issue 11 p. 925-929 Crayfish plague pathogen in invasive North American crayfish species in Hungary E Kozubíková, E Kozubíková Faculty of Science, Department of Ecology, Charles University in Prague, Prague, Czech RepublicSearch for more papers by this authorM Puky, M Puky Hungarian Danube Research Station of the Institute of Ecology and Botany of the Hungarian Academy of Sciences, Göd, HungarySearch for more papers by this authorP Kiszely, P Kiszely Balaton Limnological Institute of the Hungarian Academy of Sciences, Tihany, HungarySearch for more papers by this authorA Petrusek, A Petrusek Faculty of Science, Department of Ecology, Charles University in Prague, Prague, Czech RepublicSearch for more papers by this author E Kozubíková, E Kozubíková Faculty of Science, Department of Ecology, Charles University in Prague, Prague, Czech RepublicSearch for more papers by this authorM Puky, M Puky Hungarian Danube Research Station of the Institute of Ecology and Botany of the Hungarian Academy of Sciences, Göd, HungarySearch for more papers by this authorP Kiszely, P Kiszely Balaton Limnological Institute of the Hungarian Academy of Sciences, Tihany, HungarySearch for more papers by this authorA Petrusek, A Petrusek Faculty of Science, Department of Ecology, Charles University in Prague, Prague, Czech RepublicSearch for more papers by this author First published: 06 October 2010 https://doi.org/10.1111/j.1365-2761.2010.01199.xCitations: 16 E Kozubíková, Faculty of Science, Department of Ecology, Charles University in Prague, Viničná 7, Prague 2, CZ-12844, Czech Republic (e-mail: evikkk@post.cz) Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume33, Issue11November 2010Pages 925-929 RelatedInformation

The North American crayfish Procambarus clarkii is the carrier of the oomycete Aphanomyces astaci in Italy

Aphanomyces astaci (Saprolegniales, Oomycetes) is classified among the 100 world’s worst invasive species. This species is endemic to North America and has been introduced into Europe by imports of their hosts, the North American crayfish species. As a consequence, extensive mass mortalities involved several populations of the European crayfish. Here, we checked its occurrence in four Italian populations of Procambarus clarkii, the most widespread alien crayfish in Italy. Digital image analyses and image processing techniques were used to select micro-melanized areas in the subabdominal cuticle of 2–10 crayfish per population. All the selected areas tested positive for A. astaci ITS nrDNA specific primers; moreover, the obtained sequences clearly corresponded to A. astaci, thus revealing that P. clarkii is an active carrier of this oomycete in Italy. Decisions are to be urgently made to control the spread of both P. clarkii and A. astaci for the conservation of the indigenous crayfish biodiversity.

Distribution, Status, and Life-History Observations of Crayfishes in Western North Carolina

Abstract Approximately 390 native North American crayfish species are known, representing nearly two-thirds of the world&s crayfish fauna. The majority of these species occur in the southeastern United States. North Carolina supports a substantial proportion of that diversity with 41 described indigenous crayfish species, 12 of which are endemic, and 3 introduced species, many of which are of significant conservation interest. In the late 1990s, the North Carolina Wildlife Resources Commission (NCWRC) began a focused effort to inventory and establish baselines for monitoring populations of both native stream-dwelling and burrowing crayfishes and invasive non-native species. During 2004–2005, that effort was completed for the Hiwassee, Little Tennessee, Savannah, French Broad, Watauga, New, Catawba, and Broad river basins in western North Carolina. Twenty-four stream-dwelling species and 5 burrowing species were collected from 199 stream sites and 58 burrowing sites. New records for many species, including...

The old menace is back: Recent crayfish plague outbreaks in the Czech Republic

The crayfish plague pathogen, Aphanomyces astaci (Saprolegniales, Oomycetes), is lethal for native European crayfish species and eliminated a number of their populations during the second half of the 19th and throughout the 20th centuries. The disease is spread by non-native North American crayfish species, known to be carriers of the pathogen, which are currently thriving in many European countries. This represents one of the major threats to the recovery of populations of native crayfish (the noble crayfish Astacus astacus and the stone crayfish Austropotamobius torrentium) in the Czech Republic. While only two suspected plague-caused crayfish mass mortalities were reported in the second half of the 20th century, five mass mortalities involving both native species were found to be caused by A. astaci between 2004 and 2007, and several additional ones, though unconfirmed, are likely. We discuss possible reasons for this apparent increase in the number of crayfish plague outbreaks, and we report details of the four most recent mass mortalities in which the presence of A. astaci has been confirmed by molecular methods (PCR with species-specific primers and sequencing of the pathogen DNA) and microscopic analysis, and of additional suspicious cases of crayfish disappearance. As these plague outbreaks have been found only accidentally, it is likely that their actual frequency is higher. The Czech Republic is probably not exceptional in this respect, and plague monitoring within the whole Central Europe deserves more attention.

Detection of Aphanomyces astaci in North American crayfish by polymerase chain reaction

We present a PCR based method to detect Aphanomyces astaci in North American crayfish. Primers were designed to specifically amplify parts of the internal transcribed spacer (ITS) regions and the 5.8 rRNA gene of A. astaci. A single round and a semi-nested assay were tested for their sensitivity and specificity. Specificity of the PCR assays was tested against several closely related Aphanomyces species, other Oomycetes and some non-A. astaci DNA that might be found in or on crayfish. The single round assay was fully specific against all DNA tested. In the semi-nested assay, cross-reaction was seen when the equivalent of 40,000 or more genomic units of A. invadans or A. frigidophilus were entered into the PCR reaction. The lower detection limit of both assays lies around 1 genomic unit of A. astaci. Investigation of various parts of the exoskeleton of 3 North American crayfish species revealed that for O. limosus and P. leniusculus the telson and soft abdominal cuticle yielded a positive PCR reaction most frequently. For the third species, Procambarus clarkii, only 1 individual tested positive, so no conclusion as to preferred infestation site(s) could be drawn.

Behavioral Responses to 'Alarm Odors' In Potentially Invasive and Non-invasive Crayfish Species from Aquaculture Ponds

AbstractTwo North American crayfish species, the Eastern white river crayfish, Procambarus acutus acutus, and the red swamp crayfish, P. clarkii, were studied in the laboratory for their responses to food odors and to cues released by injured conspecifics and heterospecifics. The two species differ in that only P. clarkii is known to behave as an invasive species. All the test individuals were collected from aquaculture research ponds, in which they had had no prior contact with the other species and predation risks, excluding cannibalism, were reduced. The experimental design consisted in subjecting 20 crayfish per species to (1) a 3-min control phase after the injection of 20 ml of water and (2) a 3-min test phase after the injection of 20 ml of one of three test solutions (food odor, conspecific odor plus food odor, heterospecific odor plus food odor). We found that the two species differ on one hand for their background behavior and on the other for the intensity and quality of their responses to the three types of cues. Firstly, P. clarkii appeared more active than P. acutus acutus during the control phase and responded in a stronger fashion to the injection of the solutions. Secondly, we recorded an increased locomotion in P. acutus acutus with food and heterospecific cues (by moving crayfish maximize the chance of finding food), but not with conspecific odors (by not moving, crayfish reduce their exposure to visual predators). To the contrary, at the injection of the three test solutions P. clarkii displayed clear feeding-related activities (although less intense with conspecific odors) as opposed to the danger reactions shown in a previous study on individuals from a naturalized population of the same species. This result suggests that crayfish reared in an environment where predation risks are reduced (e. g. in aquaculture ponds) may respond differently to cues that in other, more risky habitats inform of a danger.