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Transglutaminase (TGase) from signal crayfish (Pacifastacus leniusculus) and its activity at low temperatures was studied. TGase is an abundant protein in the hematopoietic (HPT) cells and this tissue was used for TGase enzyme preparation. The optimal temperature and pH for the activity of crayfish TGase were determined. We found that TGase activity at 4 °C showed nearly the same activity as at a temperature of 22 °C. TGase activity from crayfish was compared with guinea pig liver TGase activity at 4 °C and the crayfish TGase displayed a higher activity while guinea pig liver TGase had a very low activity at this low temperature. By comparing kinetic parameters to guinea pig liver TGase, the results showed that a high activity of crayfish TGase was due to a decreasing Km value for pentylamine as a substrate, while it did not affect the kcat value (at 22 °C). The amino acid sequences of a krill and a crayfish TGase, which both are cold adapted, do not give any clue to why these two enzymes are cold-adapted. These results demonstrate that crayfish TGase is adapted to have significant activity at low temperatures and since crayfish are living in quite cold waters this is an interesting adaptation of this enzyme.

The data presented here corresponds to the research paper “Simultaneous detection of invasive signal crayfish, endangered white-clawed crayfish and the crayfish plague using environmental DNA”. A crayfish-specific assay was designed and optimised using three real-time PCR supermixes (SYBR™ Green, SsoFast™ EvaGreen® and HOT FIREPol® EvaGreen®). Diagnostic high resolution melt (HRM) data from direct application of assay on both ex-situ eDNA water samples and field samples from four catchments (two in Wales, two in England) is presented in this article, displaying positive HRM profiles for invasive signal crayfish (Pacifastacus leniusculus), native white-clawed crayfish (Austropotamobius pallipes) and crayfish plague causal agent (Aphanomyces astaci). Keywords: Pacifastacus leniusculus, Austropotamobius pallipes, Crayfish plague, HRM-qPCR, eDNA

Metal pollution is a long-standing concern and bioindicators are commonly used in ecotoxicological studies to monitor impacted wildlife populations for evidence of sublethal effects. Significant variation in the response of common biomarkers to metals is reported across taxa, thus necessitating careful characterization in model organisms. In this study, we describe the regulation of glutathione S-transferase (GST), glutathione (GSH), and metallothionein (MT) by zinc chloride (0.6, 0.9, 1.2, 2.4, 4.8, 9.6 μg g(−1)) and copper chloride (0.6, 0.9, 1.2 μg g(−1)) in signal crayfish (Pacifastacus leniusculus). Zinc chloride did not alter GST activity relative to controls in the hepatopancreas. Crayfish exposed to copper chloride exhibited decreased GST activity at the lowest dose tested (0.6 μg g(−1)) with no change observed at the higher doses. GSH did not change in response to either metal when sexes were grouped together. MT concentrations increased in response to zinc (2.4, 4.6, and 9.6 μg g(−1) doses) and copper (0.6, 0.9, and 1.2 μg g(−1) doses) in gill tissue. In tail tissue, MT increased at the 2.4 and 4.8 μg g(−1) zinc chloride doses and all the concentrations of copper tested. Sex-specific differences in endogenous antioxidant expression were also analyzed with no clear patterns emerging. We concluded that these endpoints are sensitive to zinc and copper in signal crayfish, although careful interpretation is needed when applying them in field studies given the variation in responses, non-monotonic dose responses, and differences in biotic and abiotic factors that inevitably exist in different aquatic ecosystems.

The crayfish plague pathogen (Aphanomyces astaci) causes mass mortalities of European crayfish when transmitted from its original North American crayfish hosts. Little is known, however, about interspecific transmission of the pathogen between different American crayfish species, although evidence from trade of ornamental crayfish suggests this may happen in captivity. We screened signal and virile crayfish for A. astaci at allopatric and sympatric sites in a UK river. Whilst the pathogen was detected in signal crayfish from both sites, infected virile crayfish were only found in sympatry. Genotyping of A. astaci from virile crayfish suggested the presence of a strain related to one infecting British signal crayfish. We conclude that virile crayfish likely contracted A. astaci interspecifically from infected signal crayfish. Interspecific transmission of A. astaci strains differing in virulence between American carrier species may influence the spread of this pathogen in open waters with potential exacerbated effects on native European crayfish.

The effects of chloridazon (Ch) and its metabolite chloridazon-desphenyl (Ch-D) at the environmentally relevant concentrations of 0.45 µg/L and 2.7 µg/L on signal crayfish Pacifastacus leniusculus were assessed in a 30-day exposure followed by a 15-day depuration period. Locomotion, biochemical haemolymph profile, oxidative and antioxidant parameters, and histopathology were evaluated. Crayfish exposed to Ch at 0.45 µg/L and 2.7 µg/L showed significantly (p

The spread of non-indigenous crayfish species poses a threat to local populations of crayfish as well as to other fauna and flora across Europe and around the world. Several methods have been used in attempt to reduce their numbers and stop their further spread. Crayfish barriers are the best way to stop the non-anthropogenic spread of established invasive crayfish populations. Up to now there are very few published papers regarding crayfish barrier design and practical experience in construction. For the last seven years, we have optimised construction and functionality of crayfish barriers, tested various building materials and planned construction of many barriers across Switzerland. In this article, we highlight our experience, share the acquired knowledge and present the newest findings regarding considerations, which must be made when planning a barrier to stop the upstream movement of non-indigenous crayfish species. From our experience we conclude that crayfish barriers work in preventing the movement of invasive species if certain factors are taken into account. Barrier design and construction must be specific for each project, because the size of the watercourse, flow velocity, bank conditions, existing constructions and accessibility, all change the way a barrier should be set-up.

After mating, spermatophores of signal crayfish are stored on the body of the female for a period before fertilization. This study compared the post-mating protein profile and pattern of protein tyrosine phosphorylation of the signal crayfish spermatophore to that of the freshly ejaculated spermatophore and found substantial differences. Two major bands of tyrosine-phosphorylated proteins of molecular weights 10 and 50 kDa were observed in the freshly ejaculated spermatophore of the signal crayfish. While the tyrosine-phosphorylated protein band with molecular weight 10 kDa was formed by protein(s) of similar pH, the band with molecular weight of 50 kDa consisted of proteins of varying pH. In the post-mating spermatophore, the band with molecular weight of 50 kDa was not detected, and an increase in the level of protein tyrosine phosphorylation was observed in the 10 kDa band. The microtubular radial arms of the spermatozoon showed a positive reaction to an anti-tyrosine antibody conjugated with gold particles in both the freshly ejaculated and post-mating spermatophores. In conclusion, the male gamete of the signal crayfish undergoes molecular modification during post-mating storage on the body of the female including changes in the level of protein expression and protein tyrosine phosphorylation. Structural similarity of the radial arms in the crayfish immotile spermatozoon with flagellum, which is the main site of protein tyrosine phosphorylation in the mammalian motile spermatozoa, raises questions regarding evolution and function of such organelles across the animal kingdom that must be addressed in the future studies.

Invasive species represent one of greatest threats to aquatic biodiversity globally and are widely acknowledged to be instrumental in modifying native community structure. Despite this, little is known about how the increasing range expansion of invasive taxa may affect routine biomonitoring tools widely employed to measure or quantify environmental quality in lotic systems. This study examined the impact of an invasive freshwater crayfish on commonly employed riverine macroinvertebrate biomonitoring tools (scores and indices) designed to respond to a range of stressors. Data from long-term monitoring sites on both ‘control’ and invaded rivers in England were examined to assess changes to biomonitoring scores following invasion by signal crayfish ( Pacifastacus leniusculus ). Results indicate that routine biomonitoring tools used to quantify potential ecological stressors which are weighted by abundance, such as the Lotic-invertebrate Index for Flow Evaluation (LIFE) score and Proportion of Sediment-sensitive Invertebrates (PSI), were subject to significant inflation following invasion. In contrast, indices based simply on the presence of taxa, such as the Average Score Per-Taxon (ASPT – a derivative of BMWP), displayed no changes compared to control rivers; or in the case of the Biological Monitoring Working Party Score (BMWP), NTAXA and EPT richness, no consistent pattern following invasion. Season had a significant effect on the interaction of crayfish and LIFE and PSI scores. Autumn samples were subject to statistical inflation following crayfish invasion whilst spring samples exhibited no significant change. The results suggest that care should be taken when interpreting routine macroinvertebrate biomonitoring data where non-native crayfish are present, or in instances where their presence is suspected.

eDNA-based methods represent non-invasive and cost-effective approaches for species monitoring and their application as a conservation tool has rapidly increased within the last decade. Currently, they are primarily used to determine the presence/absence of invasive, endangered or commercially important species, but they also hold potential to contribute to an improved understanding of the ecological interactions that drive species distribution. However, this next step of eDNA-based applications requires a thorough method development.We developed an eDNA assay for the white-clawed crayfish (Austropotamobius pallipes), a flagship species of conservation in the UK. Multiple subsequent in-situ and ex-situ validation tests aimed at improving method performance allowed us to apply eDNA-based surveys to evaluate interactions between white-clawed crayfish, crayfish plague and invasive signal crayfish.The assay performed well in terms of specificity (no detection of non-target DNA) and sensitivity, which was higher than more established traditional species survey methods. Quantification of species biomass was, however, less reliable.Comparison of eDNA sampling methods (precipitation vs. various filtration approaches) revealed that optimal sampling method differed across environments and might depend on inhibitor concentrations.Finally, we applied our methodology together with established assays for crayfish plague and the invasive signal crayfish and demonstrated their significant interactions in a UK river system.Our analysis highlights the importance of thorough methodological development of eDNA-based assays. Only a critical evaluation of methodological strengths and weaknesses will allow us to capitalise on the full potential of eDNA-based methods and use them as decision support tools in environmental monitoring and conservation practices.

The French Alps is an important area for several species of crayfish; some species are native in this region and several were introduced by humans. The present study aimed at modelling the distributions of these two categories of species and find the significant environmental variables to explain these distributions. Field sampling was performed in this region in 2014 resulting in enough data for modelling the distribution of three species, one native (the white-clawed crayfish, Austropotamobius pallipes) and two introduced from North America (the spiny-cheek crayfish, Faxonius limosus, and the signal crayfish, Pacifastacus leniusculus). Environmental data were collected from different sources and included altitude, slope, land cover, and several water quality measures such as nitrate and ammonium concentrations. The two introduced species showed different influential variables compared to the white-clawed crayfish. Currently, it is unlikely that the two introduced species affect negatively the native white-clawed crayfish. The most important threat for this species seems to be the increase of temperature caused by global warming. If the introduced species continue to spread, they may provide a synergy with the increase of temperature and threaten the native populations. It appears crucial to continue the monitoring of these species in this area. Future investigations should be carried out to understand the relationships between present crayfish spatial distribution and pathogens carried by alien species as these might be critical factors mediating the interactions among these species.

Worldwide biodiversity is suffering a “biogeographical homogenization” due to biological invasions. The translocation of freshwater crayfish around the world for aquaculture and the pet trade is also spreading their symbionts, so that all of the association's members have the potential to form invasive populations. In Europe, the signal crayfish, Pacifastacus leniusculus, is often concomitant with the branchiobdellidan Xironogiton victoriensis and through repeated translocations their ranges are expanding. In this study, we report the first observation of X. victoriensis on a native European crayfish population of Austropotamobius pallipes. This work is an alert to the authorities and decision makers on the risks to native species when aquaculture projects introduce alien crayfish species and their symbionts into an area. Future studies are needed to evaluate the impact of this non-native ectosymbiont on native crayfish populations.

Red swamp crayfish (Procambarus clarkii) and signal crayfish (Pacifastacus leniusculus) are two invasive freshwater species with a worldwide distribution. The objective of this work was to investigate how the two species move and use space in an area of recent coexistence. Simultaneously, we test the use of new tools and indices to describe their movement patterns. To accomplish this we performed a radio-tracking program within a river-type habitat during two different periods (September/October 2010 and June/July 2013). We used spatial analysis tools to map crayfish radio-location data with and without accounting for the curvature of the river. To assess the consistency of the direction of movement and of the distances traveled by crayfish, two indices were developed. To assess the habitat preferences of each species we applied Ivlev's Electivity Index and the Standardized Forage Ratio. Movement of P. clarkii and P. leniusculus differed. The average detected movement was 8.8 m day−1 for P. clarkii and 17.5 m day−1 for P. leniusculus. However, crayfish behavior ranged from almost complete immobility – sometimes during several days – to large movements, in half a day, up to a maximum of 255 m for P. clarkii and 461 m for P. leniusculus. The proportion of upstream or downstream movements was independent of the species and both species displayed no preference for either direction. The indices of consistency of movement showed a large interindividual variation. Species and period (2010 or 2013) affected the mean daily distance traveled, maximum observed distance from location of release and percentage of observations under vegetation cover. The Ivlev's Electivity Index and the Standardized Forage Ratio presented similar results. P. clarkii showed a preference for pool areas with riparian vegetation cover while P. leniusculus preferred riffle and pool areas with riparian vegetation cover. Our work provided new and valuable data for modeling the active dispersal of these two problematic invaders in a context of coexistence.

Assessment of population biology at early establishment stages is a fundamental component of conservation monitoring programmes, such as for invasive signal crayfish Pacifastacus leniusculus. Population structure, body condition (including its relation to density-dependence), spatial patterns and habitat relationships were examined between September and October 1997 along the lower River Stort catchment (Thames River catchment, UK). A higher proportion of females was observed at intermediate sizes, whereas the largest individuals were males. Body condition was positively associated with total crayfish abundance in females but not males. Principal components analysis of the population data (by gender and size) across sampling sites revealed three distinct groups (large males, large females, small crayfish of mixed gender), with large males having significantly (analysis of covariance) lower body condition. Multiple regression of crayfish population and habitat data revealed: increasing abundance was associated with high total suspended solids (e.g. burrowing behaviour) in all size/gender groups except medium and large males; decreasing abundances of large males and females with increasing hydrodynamic efficiency (i.e. Froude number); and increasing abundance of large males and females with increasing substratum roughness. Signal crayfish population structure in the River Stort suggests an elevated potential for dispersal and reinforcement throughout the River Lee catchment. The observed spatial and habitat segregation of crayfish by gender and size appears to reflect a female reproductive strategy that avoids contact between progeny and big aggressive/cannibalistic males. Furthermore, intra-male competition is the likely reason for the lower body condition of big males, given the lack of a negative relationship between male body condition and crayfish abundance. The comparison with established populations elsewhere shows that a sex-ratio biased towards females could be a good descriptor to detect invading populations. Potential threats posed by signal crayfish for the conservation of River Stort catchment are predation, competition and habitat alteration.

Climate change and invasive species are two major biodiversity threats expected to provoke extinctions of many species in the future. This study evaluates the joint threat posed by climate change and two invasive species: the zebra mussel (Dreissena polymorpha) and the signal crayfish (Pacifastacus leniusculus), on the distribution of two endangered freshwater species: the depressed river mussel (Pseudanodonta complanata) and the white-clawed crayfish (Austropotamobius pallipes), at the scale of Europe. We expected the native species to experience a gradual contraction over time in their geographic range size, while the invasive species would maintain or increase their spread; therefore, their overlap would increase, further threatening the conservation of the native species. To test these three hypotheses, ensemble species distribution models (SDMs) were calibrated with current distributions and projected onto present and 2050 future climatic scenarios. In agreement with our expectations, the 2050 scenarios suggested D. polymorpha may strongly benefit from climate changes (increase of 15–20% in range size), while the depressed river mussel would experience a considerable loss (14–36%), the overlap between both mussels increasing up to 24%. Although both crayfishes were predicted to be negatively affected by climate changes, the contraction was more severe for the invasive P. leniusculus (up to 32% decrease in range size). Moreover, the overlap between both crayfishes decreased by 13–16%, which may reduce the pressure upon the native A. pallipes. This study illustrates how SDMs can assist in management of endangered species over large spatial and temporal scales by identifying current and future areas of shared bioclimatic suitability and potential refugia.

The invasion of non-native signal crayfish into European ecosystems has resulted in a drastic reduction of native European crayfish, with adverse effects on ecosystems and fisheries. This study aimed to determine whether native crayfish can be protected by physical barriers that do not hinder fish migration, but prohibit the upstream migration of non-native crayfish. Laboratory experiments were carried out to test a barrier design consisting of a gently-inclined, smooth, prismatic, cross-channel structure. Barrier efficiency appeared to depend on barrier roughness, barrier slope and flow velocity directly above the barrier crest. The maximum barrier slope that can be climbed by crayfish decreases with increasing flow velocity in a non-linear way. This observation is in agreement with the physics of crayfish locomotion as demonstrated by applying Newton’s laws of motion to crayfish. Contrary to general acceptance, signal crayfish do deliberately deploy their swimming capacities to pass barriers, proving the general belief that crayfish only swim as an escape response to be untrue. This suggests that crayfish are able to pass all barriers regardless of barrier slope or barrier roughness if the flow velocity is below the maximum velocity against which crayfish can swim. Nevertheless, physical crayfish barriers are an effective method to protect indigenous crayfish in streams with sufficiently high flow velocities. Promising barrier locations are pre-existing structures such as fish ladders alongside weirs, where flow velocities are controlled, sedimentation risks are low, maintenance is done regularly and the bed profile is suitable to connect barriers to.

The specialized crayfish parasite Aphanomyces astaci causes the devastating crayfish plague in European crayfish. Even though A. astaci sporulation has been thoroughly studied under pure culture conditions, little is known about the sporulation dynamic from its live host. Our purpose was to investigate the A. astaci spore dynamic in its native parasite–host relationship by monitoring the sporulation from carrier crayfish into the ambient water using agent specific qPCR. American signal crayfish (Pacifastacus leniusculus) with known positive carrier status were housed individually and communally in two experimental set-ups using multiple replicates and different temperatures. Water samples were collected weekly, and spore numbers were quantified. We demonstrate here that live latent carrier crayfish continuously released a moderate number of A. astaci spores (∼2700 spores per crayfish/week) in the absence of death and moulting events. In contrast, a pronounced sporulation increase was seen already one week prior to death in moribund crayfish, suggesting a crayfish plague-like condition developing in weakened or stressed individuals. Significantly more spores were produced at 18 °C compared to 4 °C, while a negative correlation was detected between spore numbers and temperatures rising from 17 to 23 °C. This study is the first attempt to quantify the spore release from carrier crayfish on the basis of qPCR applied on water samples, and demonstrate that the approach successfully unravel A. astaci sporulation patterns. The results emphasize that carrier crayfish pose a constant infection risk to highly susceptible crayfish species regardless of crayfish life cycle state.

Peracetic acid (PAA) is useful in treating a wide variety of serious fish diseases in aquaculture. As no information on PAA toxicity to crayfish is available, we conducted acute toxicity tests of Persteril 36, a commercial PAA-containing product, on three age/size classes of signal crayfish, Pacifastacus leniusculus. Results confirmed high tolerance of the target species to this product, expressed as a 96 h LC50 of 77.3 ± 1.0 mg L− 1 PAA in adults and low post-treatment mortality in 9 month old juveniles. As PAA concentrations successfully applied in aquaculture are generally 2.0 mg L− 1 or lower, PAA can be recommended for use in astaciculture. After necessary evaluations, uses might include limiting spread of crayfish plague, treating saprolegniosis on artificially incubated crayfish eggs, and avoiding translocations of further crayfish-related non-native species when introducing crayfish or stocking them in closed culture systems.

Crayfish are amongst the most frequently introduced non-native aquatic organisms, with well-documented negative effects on a large number of freshwater taxa. Crayfish-control attempts often make use of manual removal by trapping, a method known preferentially to remove the largest individuals. Studies from aquaculture suggest that lowered population densities and the preferential removal of large individuals may result in non-removed individuals demonstrating increased growth rates. We test the hypothesis under wild conditions, that removal by trapping of American signal crayfish from a UK river would result in an improvement in body condition in the remaining crayfish. We studied four 100 m stretches of two rivers, the Evenlode and Thame, comprising two removal and two non-removal stretches. Each river supported both treatments. Half of the crayfish captured from the removal sections were removed and humanely destroyed by freezing. All crayfish captured from the non-removal sections were marked and returned at the point of capture. Crayfish were more likely to be captured if relatively large and with intact chelae. Catch per unit effort was reduced at the removal sites, and still remained significantly lower between capture sessions. The mean carapace length of crayfish was smaller at removal than non-removal sites. Over the course of the experiment, crayfish at the removal sites became progressively heavier for a given carapace length. The results of this study are consistent with expectations if removals reduced the population density, particularly of large, competitively dominant crayfish, resulting in higher growth rates in the remaining population. This study confirms the possibility that the effects of manual removal by trapping may be at least partially counteracted by density dependent effects improving the body condition of the non-removed portion of the population.

Considering that the use of decapsulated Artemia cysts as direct food for juvenile crayfish could be an alternative to live nauplii, a 100-day experiment was carried out under controlled conditions to evaluate the effects of cysts, comparing with nauplii, as supplement to a dry diet for salmonids on the survival and growth of juvenile signal crayfish (Pacifastacus leniusculus) from the onset of exogenous feeding (stage 2). The reduction of feeding frequency was also tested. According to a bifactorial design, six treatments, differing in the supplement and feeding frequency, were tested: the dry diet supplemented with Artemia nauplii or decapsulated cysts was supplied once a day, once every two days and once every three days. Survival rates ranged from 56.7% to 81.7%, rising significantly with increasing the feeding frequency. The highest growth (12.94 mm carapace length and 593.08 mg weight) was reached by the crayfish that received the dry diet supplemented with cysts once a day, with significant differences from the rest of the treatments. Considering the supplement, the cysts supported significantly higher growth than the nauplii. Regarding the feeding frequency, growth was higher when the food was supplied once a day, showing significant differences from the other two frequencies (once every two days and once every three days). This study shows that decapsulated cysts are better dietary supplement than live nauplii. In crustacean culture, this is the first report of successful use of Artemia cysts from the onset of exogenous feeding.

The invasive signal crayfish ( Pacifastacus leniusculus ) may undergo ontogenetic diet shifts with increasing size, but the consequences of crayfish size–structure changes for aquatic food webs are little known. We evaluated size-dependent impacts of signal crayfish on a littoral marsh food web using in-situ enclosures in a northern Japanese marsh. During the 60-day experiment, large crayfish ( 30 mm) appeared after more time had passed. Benthic algal biomass was reduced in the presence of large crayfish but was affected little by small crayfish, suggesting that large crayfish were significant bioturbators. On the other hand, total invertebrate biomass was reduced while total invertebrate density was enhanced in the presence of both crayfish size classes. Potential crayfish impacts on invertebrates are: (1) predation on large vulnerable taxa such as Trichoptera and predatory invertebrates, (2) mechanical destruction of macrophytes, thereby reducing microhabitats for invertebrates, (3) heightened emigration of invertebrates in response to bioturbation and/or (4) predation or competition release on small invertebrates as a result of crayfish reducing their predators/competitors. Invertebrate taxa richness was nearly halved in the presence of large crayfish, probably reflecting reductions of rare taxa. Overall, functional roles of signal crayfish as omnivores and ecosystem engineers remained similar during the ontogenetic stage but the magnitude and rate of crayfish impacts intensified with increasing crayfish size. Thus, removal of large invasive crayfish alone may reduce detrimental impacts on aquatic biodiversity.

The aim of this study was to determine the possibilities of increasing egg density in artificial incubation using low flow rates. Eggs of signal crayfish ( Pacifastacus leniusculus ) were incubated at three densities: 6.6, 20 and 42 eggs cm − 2 and two flow rates: 0.5 and 1 l min − 1 (0.0095 l cm − 2 min − 1 and 0.019 l cm − 2 min − 1 , respectively). Formaldehyde doses of 3000 and 2500 ppm were administered as antifungal treatment. In experiment 1, the best survival to stage 2 juvenile (84.3%) was obtained with the administration of 3000 ppm of formaldehyde at a density of 6.6 eggs cm − 2 , but differences were not significant either with a higher density (20 eggs cm − 2 ) or with a lower formaldehyde concentration (2500 ppm). In experiment 2, the best final survival (88.8%) was obtained with the administration of 2500 ppm of formaldehyde at a density of 20 eggs cm − 2 , and a flow rate of 0.5 l min − 1 (0.0095 l cm − 2 min − 1 ), without significant differences either with the same density and a flow of 1 l min − 1 (0.019 l cm − 2 min − 1 ), or with the density of 42 eggs cm − 2 (around 86%). The progressive reduction of formaldehyde concentration we have tested may have found its limit at 2500 ppm since, although was shown to be effective, a light fungal growth could be observed. Nevertheless, with 3000 ppm the growth of fungi was kept out completely with densities up to 20 eggs cm − 2 . Antifungal treatment seems to be a key factor to make feasible artificial incubation of crayfish eggs at high densities such as 42 eggs cm − 2 , even with a limited water flow.

The number and duration of agonistic encounters between signal crayfish Pacifastacus leniusculus individuals were monitored in two different social environments: a “stable” environment with large size variation and in an “unstable” environment with narrow size variation of conspecifics. The number of the agonistic interactions was higher in the “stable” environment. However, aggressive encounters lasted indicatively (P = 0.098) longer in the “unstable” social environment. The number of encounters decreased significantly over the course of the communal rearing in both environments. The crayfish were kept individually before and after the communal rearing and growth and food consumption were measured. Both growth and food intake decreased when the animals were reared communally in comparison to the individual phases. The amount of cheliped, leg and antennal injuries did not differ between the two social environments, however, their occurrence increased during the communal rearing. These results suggest that the social environment of crayfish (the size variation of conspecifics) affects the number and the duration of agonistic encounters, while the absence of conspecifics (individual vs. communal) influences growth, food intake and the number of injuries. In a “stable” environment, fighting success was based on animal size. This was not the situation in an “unstable” environment, indicating the important role of behaviour on social hierarchy under conditions where size variation is limited, e.g. in restocked natural populations or aquaculture. Feeding success correlated poorly with fighting success and, therefore, feeding hierarchy does not reliably describe social hierarchy in crayfish populations.

Two 100-day experiments were carried out under controlled conditions in order to evaluate the effects of different combinations of a dry diet supplemented with live feed on survival and growth of juvenile Pacifastacus leniusculus Dana juveniles from the onset of external feeding. In the first experiment, juveniles were subjected to five feeding and density conditions: a dry diet for rainbow trout (D) with a density of 50 animals m− 2, the same dry diet supplemented with Artemia nauplii for 20, 60 or 100 days (50 m− 2) and D supplemented with Artemia nauplii for 100 days at a density of 200 m−2. When juvenile crayfish did not receive live feed supplement, mean survival rate (11.33%) and growth were significantly lower. The highest survival rates were obtained when nauplii were added for 100 days (57.83% and 57.33%). Survival rates in the two densities were similar but growth was significantly higher at the lowest one. When the period of supplementation was reduced to 20 or 60 days, survival rates decreased significantly. In experiment 2, amount and frequency of Artemia supply were increased and freshwater zooplankton (Daphnia pulex) was used as supplement of D. An increased frequency (three times a week) and amount of live food supply led to high survival rates (up to 82%) and growth (Carapace length: 11.79 mm, Weight: 360.16 mg). From these results it can be deduced that live feed can be the source of some nutritional factors needed for astacid juvenile crayfish from the onset of external feeding to guarantee the viability during the first months of life.

Individual food intake of two-year-old signal crayfish (Pacifastacus leniusculus Dana) juveniles (initial carapace length 22.81 ± 1.68 mm and wet weight 3.08 ± 0.67 g) fed semi-moist gelatine-based food were measured four times (days 28, 43, 64 and 91) during a three-month experimental period. Food intake competition results between juveniles from three separate groups was evaluated with the help of feeding ranks that were assessed on the basis of the individual mean values of consumption data from repeated radiography measurements. Signal crayfish juveniles showed high variability in food intake both among juveniles in a group (inter-individual) and within individuals day-to-day variation (intra-individual). This unequal distribution of food resources and its relation to animal size as a main factor to control food intake suggested feeding hierarchy among crayfish juveniles reared communally. This is supported by observed low day-to-day variations in food intake among juveniles with high consumption. The relationship between competition success and size-based dominance were analysed with the change of individual carapace length rank during the experiment based on growth and food consumption data. It seemed that signal crayfish juveniles can raise their rank either by consuming high amounts of food or being very efficient.

In artificial incubation of astacid crayfish eggs, the use of effective antifungal treatments is advisable for controlling the spread of fungi from dead to healthy eggs and increasing final efficiency rates. The aim of this study was to evaluate the effectiveness of formaldehyde, malachite green, hydrogen peroxide, isopropyl alcohol, copper sulfate, potassium permanganate and iodine (as polyvidone iodine) on signal crayfish ( Pacifastacus leniusculus Dana) eggs incubated at 6.6 eggs/cm 2 for long periods (up to 71 days). The administration of 3000 ppm formaldehyde for 15 min every other day up to the beginning of hatching allowed a stage 2 juvenile survival rate of 74.5%, without significant differences with 15 ppm malachite green (81.5%). These treatments did not show differences with the 150,000 ppm isopropyl alcohol dosage (65.5%). Formaldehyde at 3000 ppm can be administered up to the beginning of moulting to stage 2, without affecting the survival rates. Formaldehyde and malachite green treatments effectively controlled fungi. However, isopropyl alcohol and copper sulfate weakly inhibited mycelial growth only at the highest concentrations (150,000 and 18 ppm, respectively). Hydrogen peroxide below to 1500 ppm was insufficient to control fungi resulting in low survival rates to juvenile stage 2 (

Studies carried out to evaluate reproductive efficiency from maturing up to juvenile stage 2 production in astacid crayfish are scarce. Research with a view to determining total losses over the whole reproductive cycle is required. Two experiments were carried out with Pacifastacus leniusculus to obtain data on reproductive efficiency in earthen ponds and under laboratory conditions, in each case with two different densities of animals. All the parameters recorded were related to the initial number of females. In earthen ponds, numbers of egg-bearing females close to hatching (April) showed no significant differences between the two densities (76.1% with 3.4 breeders/m 2 and 72.5% with 6.6 breeders/m 2 ), with an estimated mean of 228 eggs per female. In the laboratory, 81.3% and 75% of females yielded stage 2 juveniles at densities of 6 and 12 breeders/m 2 , respectively, with an average of 135.4 juveniles per initial female, achieving an efficiency from first to final count around 70%. Productivity results are discussed with relation to those attained in other astacid species.

During the artificial incubation, fungi can grow over nonviable eggs and invade the healthy ones causing a decrease of efficiency rates. Thus, the use of antifungal substances must be considered. Different doses and treatment frequencies of formaldehyde, hydrogen peroxide, sodium chloride and malachite green were tested on eggs of signal crayfish (Pacifastacus leniusculus Dana). Eggs were incubated at two densities: 2.2 and 6.6 eggs/cm2. The highest efficiency to stage 2 juvenile (67.3%) was obtained with formaldehyde (4500 ppm) applied for 15 min three times a week up to the beginning of hatchings, without significant differences with the same treatment applied twice a week neither with malachite green (15 ppm). In both cases, the fungal growth was effectively inhibited. The formaldehyde dose of 1500 ppm administered every 3 days, as well as hydrogen peroxide and sodium chloride treatments, were insufficient to control fungi. It was detected a positive effect when density was reduced, so that with 2.2 eggs/cm2, a final efficiency of 71% was obtained even without antifungal use; while with 6.6 eggs/cm2, it was 22.6%.

The effect of stocking density on growth and survival of Pacifastacus leniusculus (Dana) juveniles was evaluated. P. leniusculus stage 2 juveniles (average weight 21.3±4.1 mg and average carapace length [CL] 5.2±0.3 mm) were stocked in 0.42 m 2 tanks at 100, 200, 400 and 800 individuals/m 2 and reared for 91 days at 18.4±0.4 °C. Final mean weight and mean length were found to decrease with increasing stocking densities. When doubling the stocking density the predicted reduction of the final wet weight is about 74 mg/individual (13–17%) and the corresponding decrease in carapace length was 0.51 mm (about 4%) over the experimental period. The survival of the animals was also affected by stocking density; the model suggests a decrease of 11% units in the survival when the stocking density is doubled. Furthermore, the proportion of lost chelipeds was found to be dependent on the stocking density. No density effects were found on the parameters describing the within tank length distributions of individual animals. These data suggest that the culture of P. leniusculus is feasible at the density groups tested but 200–400 juveniles/m 2 is recommended for intensive juvenile culture in the first 3 months growing season.

Use of the lipofuscin ageing method as a crustacean fisheries research tool requires a calibration of tissue lipofuscin concentration to chronological age that is applicable to the natural population under investigation. Current approaches, involving known-age individuals or analysis of cohorts in neurolipofuscin concentration frequency distributions of the wild population, have advantages and disadvantages. A possible alternative that could be applied to individuals of unknown age involves initial biopsy of lipofuscin-loaded tissue from an eyestalk followed, after a known time period, by sampling of the second eyestalk, providing two successive lipofuscin measurements from the same individual and, thus, the neurolipofuscin accumulation rate in the intervening period. We tested the feasibility of this approach by examining the effect of eyestalk removal itself on subsequent lipofuscin accumulation in the remaining eyestalk using known-age individuals of a convenient decapod model, the signal crayfish, Pacifastacus leniusculus. By comparison with untreated controls, a 61% reduction in average neurolipofuscin accumulation rate in the remaining eyestalk occurred. It is hypothesized that this represents either slowed lipofuscinogenesis due to reduced oxidative metabolism or glycosylation, or increased lipofuscin loss due to enhanced proteolytic or phagocytic activity. It is recommended that the proposed ablation technique not be used for calibration of lipofuscin-based age determinations due to its unpredictable effect on lipofuscin accumulation.

We studied the distribution patterns of the native European white-clawed crayfish (Austropotamobius pallipes) and the introduced signal crayfish (Pacifastacus leniusculus), and looked at the water chemistry in several streams in the north of the Iberian Peninsula (Cantabrian watershed). Fifty fluvial reaches which were currently or previously inhabited by crayfish and had physical attributes similar to the known habitat requirements of crayfish were sampled. P. leniusculus was the most common species encountered (54% of the samples), A. pallipes was found in 19% and neither species was recorded in the remaining reaches. In this paper we determine the relationship between crayfish presence and water chemistry. As neither species inhabits waters with the highest NO2– concentrations found, it seems both species are sensitive to NO2–. Mg+2 and SO4–2 concentrations are the factors separating sites with and without crayfish (crayfish inhabit water with higher concentrations of both cations). The main differences between reaches inhabited by native and signal crayfish lies in SO4–2 concentration: higher concentrations favour signal crayfish. Applications to management based on the river water chemistry are proposed.

Signal crayfish (Pacifastacus leniusculus) originating from Lake Tahoe, California, were introduced into Karisjarvi, a small (11 ha) lake in central Finland (61° 58'N, 25° 32'E), in 1968 and 1969. Since then, the population has been monitored regularly by trap catches. The stocked signals (3–5 years old) were caught until 1973, by which time they had reached ages of 7–9 years. Catches have increased slowly since the early 1980s, the peak occurring in 1991 at 2.0 individuals per trap per night. The population size was estimated as 60 trappable specimens in 1974, 95 in 1981 and 420 in 1988. The mean density of adult population in suitable biotopes was low, 0.07 specimens per m–2, or 0.3 per shore metre, in 1988. The slow development of the P. leniusculus population has been attributed to environmental factors, mainly the limited area of good crayfish habitat. More than 90 % of all signal crayfish were caught in one-third of the shore area, i.e. in steeply sloping lake beds suitable for burrowing or rich in shelters such as rocks and submerged trees. The signals avoided flat, soft bottoms. Fifty per cent of the female P. leniusculus matured at 90 mm TL (smallest 64 mm), i.e. half of the females entered the breeding population in the autumn of their fourth year. The mean size of newly hatched (stage 2) juveniles was 9.7 mm TL and of one-summer olds 30.3 mm. The largest specimen trapped measured 159 mm. The signal crayfish imported into Finland and stocked were infected with crayfish plague (Aphanomyces astaci), but no mortality has been recorded. Two Branchiobdellidae (Annelida, oligochaeta) epibiont species new to Finland were imported from North America with P. leniusculus. The continuous occurrence of these commensals in the signal crayfish population indicates that they have adapted to Finnish conditions.

Signal crayfish, Pacifastacus leniusculus (Dana), a native of North America, were introduced into the River Great Ouse, the major lowland river in mid- to eastern England in 1984. The present paper reports the growth and reproduction of a naturalised signal crayfish population in the river. Crayfish moulted between April and October. Males of individuals >55 mm carapace length (CL) and females of individual >45 mm CL moulted only once a year while younger ones moulted more than once. Mature males grew faster than mature females by a larger per moult increment (MI) and more frequent moult. For crayfish >30 mm CL, the MI increased with CL and then decreased as crayfish grew larger, while the percentage moult increment (PCMI), the annual moult increment (AMI), and the annual percentage moult increment (APCMI) decreased with increase in CL. The mean AMI of males (36–70 mm CL) ranged from 11.7 to 5.1 mm in CL, that of females (41–70 mm CL) 8.4 to 3.4 mm. Both males and females matured in their third year. The smallest ovigerous female was 36.3 mm CL. In 1994, the mean number of pleopodal eggs per ovigerous female sampled at the end of April was 158. A recruitment of 70 juveniles per m2 was estimated in the original pool of crayfish introduction.

The feeding ecology of the introduced signal crayfish Pacifastacus leniusculus (Dana) was studied in the River Great Ouse, the major lowland river in mid- to eastern England. A total of 22 food groups were categorized from the gut contents. They showed that P. leniusculus is an omnivorous species. In terms of frequency of occurrence or gravimetric composition, the top five main diets for all sizes of crayfish in four seasons were similar. They were vascular detritus, filamentous green algae Cladophora , crayfish fragments, Chironomidae, and Ephemeroptera. Signal crayfish showed season-related feeding habits. Vascular detritus and Cladophora were ingested most frequently by all sizes of crayfish throughout the year, especially in the autumn and winter. Adult crayfish (>45 mm in carapace length) consumed more Chironomidae in the spring while consumed more Tricoptera in the summer. Coleoptera were consumed more by the young-of-the-year (YOY) in the spring. Signal crayfish also had size-related feeding habits. The larger the crayfish, the more vascular detritus was ingested. The frequency of occurrence of Cladophora was increased with crayfish size in the winter while that was higher for the median sized crayfish (20–45 mm in carapace length) in the summer. Fish were predated mainly by adult crayfish in the summer and autumn. Cannibalism occurred mainly in the summer and autumn and increased with crayfish size. Epheroptera were increasingly consumed with crayfish size in the summer while Coleoptera were consumed only by the YOY. The rations estimated for three 8-h periods of a day showed that P. leniusculus is a typical nocturnal feeder. The estimated daily ration ranged from 0.22 to 6.02% of crayfish body wet weight with higher rations in the adults than juveniles and in the summer and autumn than other seasons. The gross efficiency of food conversion decreased rapidly with increase in crayfish size.

Two isolates of Aphanomyces astaci obtained from diseased white-clawed crayfish (Austropotamobius pallipes) in Herefordshire, England were compared against representative isolates of three groups of the fungus found in Sweden and one from Spain by means of random amplification of polymorphic DNA (RAPD). The English isolates proved to be very similar to a Swedish strain which is considered to have been introduced from North America with shipments of the signal crayfish (Pacifastacus leniusculus) from 1970 onwards, and has since spread to indigenous populations of noble crayfish (Astacus astacus). This strain has not been found to be involved in recent incidences of crayfish plague in Turkey and Spain. It is therefore most likely that at least some of the outbreaks of crayfish plague in England resulted from imports of P. leniusculus from northern Europe after 1970, or directly from North America.

This study presents a revised method for the extraction of mitochondrial genome (mtDNA) from crayfish species of aquacultural interest, Pacifastacus leniusculus. The mean size of the mitochondrial genome is approximately 18,000 bp. Restriction fragment length polymorphism (RFLP) analysis performed on the mtDNA has revealed extensive genetic variability within this species. The estimated percentage of nucleotide sequence divergence among the four haplotypes found for P. leniusculus ranges from 1.16 to 3.99%. These data suggest that RFLP analysis of mtDNA may provide greater resolution than protein electrophoresis for population identification among signal crayfish populations. This marker offers new avenues for aquaculture and for understanding the genetic structure and evolutionary history of crayfish populations.

As part of investigations of the ecological impact and transmission of the crayfish parasite Psorospermium haeckeli , a laboratory experiment was performed where noble crayfish, Astacus astacus , and signal crayfish, Pacifastacus leniusculus , from populations in which P. haeckeli had not been detected, were fed with each other in all combinations. Noble crayfish fed noble crayfish did not acquire P. haeckeli during the experimental period of 10 months, while noble crayfish fed signal crayfish did. Signal crayfish fed noble crayfish showed a lower frequency of definitive positive infestation than signal crayfish fed signal crayfish. The results support the theory that Psorospermium haeckeli has been introduced to the Baltic island of Gotland with signal crayfish, and that signal crayfish, when not infected with the crayfish plague fungus Aphanomyces astaci , is more successful in suppressing the parasite. The investigations also showed that the technique of digesting soft tissues might be an inadequate method of observing P. haeckeli in signal crayfish.

Four experiments were carried out in order to evaluate survival and growth rates of Stage 2 juvenile Pacifastacus leniusculus under different management conditions: effects of offspring origin (artificial incubation, maternal incubation under laboratory conditions and maternal incubation under natural conditions), of different shelter availability, of water circulation systems (partially re-circulated and full flow-through), and effects of certain flow rates. Juveniles kept singly, rather than in groups, had higher survival rates. However, when juveniles were in groups, they showed faster growth. Offspring from artificial incubation did not show significant differences in survival and growth rates from those from maternal incubation. The addition of pebbles as shelter did not improve survival rates. The use of a full flow-through system allowed significantly higher survival and growth rates. A flow rate of 1 l/min improved the survival rate in comparison with 6 l/min, but not growth. In general, the highest mortality occurred during the first 40–60 days of the experiments, although a great variation in the final results was observed.

Arbitrary primers and the DNA polymerase chain reaction (PCR) technique were applied to study genetic variation between different strains of the crayfish plague fungus, Aphanomyces astaci. Eight different primers among 15 tested were chosen for a comparative analysis of the different A. astaci strains. On average, each primer gave rise to 5–8 bands and a majority of the bands was polymorphic for at least some strains. Two main groups among the different Swedish isolates were clearly discernible. One group included isolates from the indigenous crayfish species Astacus astacus and one isolate from As. leptodactylus originating from Turkey. The other main group included fungal isolates from both As. astacus and the introduced North American crayfish Pacifastacus leniusculus. In this latter case it seems likely that the introduced American signal crayfish has served as a vector and transmitted the pathogen to the indigenous crayfish.

An outbreak of crayfish plague (caused by the fungus Aphanomyces astaci) is described in white-clawed crayfish, Austopotamobius pallipes, in enclosed pond culture in an area of England from which no disease outbreaks have yet been reported. Signal crayfish, Pacifastacus leniusculus, from commercial culture, introduced to adjacent ponds shortly before the disease outbreak, appear to have been the disease carriers.

A large number of sites throughout the United Kingdom have been stocked with signal crayfish, Pacifastacus leniusculus . This paper describes the growth and survival of an enclosed population of this species in the southern United Kingdom. Analysis of size data from trapping records indicates that growth in the study population is at least as good as that reported from elsewhere in Europe. Maximum sizes of 75.0 mm and 68.5 mm carapace length, for males and females, respectively, were recorded. Growth of the initial implants was very good but declined slightly as density increased and habitat resources were utilised. Approximately 20% survival of introduced juveniles to catchable adults was calculated from estimates of population size. These data also permitted calculation of adult density as 1.8 m −2 . Subsequent harvesting had a detectable effect on catch per unit effort. The benefits and drawbacks of introducing a fast growing, alien species, resistant to the crayfish plague are discussed in relation to the status of Austropotamobius pallipes , the single, disease-susceptible native species.