Successful storage and transport of eggs of the white-clawed crayfish (Austropotamobius pallipes Lereboullet)

Embryonated eggs of theEuropean native white-clawed crayfish Austropotamobius pallipes Lereboullet weresubjected to three periods of storage usingpolystyrene boxes and, afterwards, artificiallyincubated. At the end of the longest storage(42 days) survival rate was 98.3%, with 65%developed to stage 2 juvenile. Differentstorage periods allowed the staggeredproduction of juvenile batches within a monthperiod. The same containers used for storagewere also suitable for transport.     

Effects of shelter type and food supply frequency on survival and growth of stage-2 juvenile white-clawed crayfish (Austropotamobius pallipes Lereboullet) under laboratory conditions

Two shelter substrates (fibre-cement sheets and PVC pipes) and two foodsupply frequencies (once and twice daily) were tested on white-clawed juvenilecrayfish in two separate experiments performed under laboratory conditions.Juvenile crayfish were maintained at an initial density of 50 animals persquaremetre in a flow-through system and fed on fresh Daphniapulex and a feed formulated for rainbow trout. After 120 days,highersurvival (50.5%), but lower growth, was obtained when fibre-cement sheets wereprovided as shelter. A comparison between food supply frequencies showed abetter survival rate (60.5%) when food was provided twice per day althoughtherewere no differences in growth after 80 days of trial. The number of animalswith chela autotomy is positively correlated (r between 0.33 and 0.48 depending ontreatments) with decreases in survival rate. The combination of adequate shelterand frequency of food supply could reduce the agonistic behaviour of juvenilecrayfish.     

Effects of stripping time on the success of the artificial incubation of white-clawed crayfish, Austropotamobius pallipes (Lereboullet), eggs

One of the main limiting factors in the use of artificial incubation techniques on crayfish farms has been the widespread belief that eggs should be stripped from females in the late stages of embryogenesis. In order to disprove this idea, three different times for egg removal were tested in white-clawed crayfish, Austropotamobius pallipes (Lereboullet): (1) just before the gastrulation process (mean degree days= 335, 34 days after spawning); (2) when the embryo was between the closing of the blastopore and the appearance of mandibular rudiments (mean degree days= 524, 56 days after spawning); and (3) when the embryo had thoracic appendage rudiments (mean degree days= 810, 92 days after spawning). The results showed that it is possible to attain acceptable survival rates up to juvenile stage 2 (51%), even when eggs have been detached at the earliest time (34 days after spawning), in such a way that artificial incubation is used for more than three-quarters (75.7%) of the total duration of the embryonic development. Factors such as the incubation device, water quality and incubation conditions have a major influence on the success of the process. Finally, a critical period was observed during the last stages of development in the present study, particularly between the eyed stage and juvenile stage 2, with mortality rates of between 26.7% and 56%.     

An intranuclear bacilliform virus associated with near extirpation of Austropotamobius pallipes Lereboullet from the Nant watershed in Ardéche, France

White-clawed crayfish, Austropotamobius pallipes, were endemic to the Nant watershed, Ardéche, France, until they were extirpated by epizootic mortality at the beginning of the twentieth century. A. pallipes were successfully reintroduced to the Nant watershed in the middle of the twentieth century. However, epizootic mortality was observed in the Nant watershed in the summer of 2000 during which time A. pallipes was extirpated from downstream regions. Dead and moribund crayfish were again detected in several episodes in summer 2001 and by October the range of A. pallipes was reduced to the headwaters of just one of the three streams in the watershed. Water quality for the watershed in summer 2001 was appropriate for crayfish habitation. Bacteriology and mycology on A. pallipes collected during several of the mortality episodes in 2001 failed to reveal a cause. However, histopathology revealed a high occurrence of intranuclear eosinophilic inclusions in hepatopancreatocytes of A. pallipes . The nuclei were hypertrophic and contained bacilliform virions consisting of a cylindrical nucleocapsid surrounded by a trilaminar envelope. Virions in section were approximately 63 × 258 nm and nucleocapsids were approximately 52 × 225 nm. It is unclear whether the intranuclear bacilliform virus was the cause of the mortality episodes or was a contributor to a disease complex involving one or several other undetected pathogens.     

Effects of shelter type and food supply frequency on survival and growth of stage-2 juvenile white-clawed crayfish (Austropotamobius pallipes Lereboullet) under laboratory conditions

Two shelter substrates (fibre-cement sheets and PVC pipes) and two foodsupply frequencies (once and twice daily) were tested on white-clawed juvenilecrayfish in two separate experiments performed under laboratory conditions.Juvenile crayfish were maintained at an initial density of 50 animals persquaremetre in a flow-through system and fed on fresh Daphniapulex and a feed formulated for rainbow trout. After 120 days,highersurvival (50.5%), but lower growth, was obtained when fibre-cement sheets wereprovided as shelter. A comparison between food supply frequencies showed abetter survival rate (60.5%) when food was provided twice per day althoughtherewere no differences in growth after 80 days of trial. The number of animalswith chela autotomy is positively correlated (r between 0.33 and 0.48 depending ontreatments) with decreases in survival rate. The combination of adequate shelterand frequency of food supply could reduce the agonistic behaviour of juvenilecrayfish.     

Physical and chemical water requirements of the white‐clawed crayfish (Austropotamobius pallipes) in western France

• 1. In France, the distribution of the native white‐clawed crayfish (Austropotamobius pallipes) is restricted, fragmented and mainly located in headwater streams. To conserve this indigenous species, it is necessary to characterize its habitat preferences.
• 2. Seven brooks in the Deux‐Sèvres Département (western France) containing wild populations of A. pallipes were studied to determine its ranges of tolerance to 19 physical and chemical water parameters. On two brooks, the Sèvre Nantaise and the Verdonnière, sites with and without A. pallipes were compared. Each site was sampled twice monthly from November 2002 to November 2004.
• 3. It was found that the white‐clawed crayfish was able to tolerate wide ranges of values of some of the measured parameters. The Magot site harboured the largest A. pallipes population (17.5 crayfish m^?2) and had dissolved oxygen concentrations as low as 4.93 mg L^?1, while water temperature rose above 20°C for several consecutive days during summer and nitrate concentrations were always found to be above 30 mg L^?1. These unusual findings could call into question the status of A. pallipes as a bioindicator of good water quality.
• 4. Principal component analyses (PCA) suggested that an increase of organic matter was a discriminant factor for the presence or absence of A. pallipes. In addition, sites with and without crayfish on the Sèvre Nantaise brook showed showed significant differences (p<0.05) in total organic carbon (TOC), and those on the Verdonnière brook in turbidity and total suspended solids (TSS).

Copyright © 2006 John Wiley & Sons, Ltd.     

Conserving indigenous crayfish: stock assessment and habitat requirements in the threatened Austropotamobius italicus

• 1. As part of the Austropotamobius pallipes species complex, the crayfish Austropotamobius italicus is a species of community interest whose preservation requires the designation of Special Areas of Conservation (SACs) (Annex II, EU Habitats Directive). This study aimed at (1) assessing the conservation status of this threatened indigenous species by stock assessment in central Italy and (2) identifying some aspects of its elective habitat.
• 2. Surveys were conducted in nine streams harbouring A. italicus (streams WI) and in 10 streams where crayfish populations became extinct at least 5 years before the study (streams WO).
• 3. The results confirmed that A. italicus is a K‐selected species, with a relatively slow growth rate (males: 0.34; females: 0.37) and a long life expectancy (males: 8.2 years; females: 7.8 years). The extant populations are healthy, showing balanced sex‐ratios and well structured age‐class compositions. Mortality is mainly due to fishing, which is illegal in Tuscany.
• 4. Principal Components Analyses showed that the streams WI and WO differ in the abundance of allochthonous plant detritus but not in the taxonomic composition of their macroinvertebrate communities. Age classes were found to be spatially segregated, juveniles mainly using cobbles as substrates and adults seemingly avoiding them.
• 5. The loss of the pristine riverine landscape seems to have been responsible, together with illegal fishing, for the local extinction of the species. As a consequence, retaining, enhancing, and restoring the habitat and its complexity are required for the preservation of A. italicus.
• 6. The designation of SACs might help in this endeavour if accompanied by programmes aimed at publicizing the need for conservation of this species. Unfortunately, crayfish‐focused projects supported by LIFE in Italy since 1992 (4%) and the SACs involved (1.4%) have been relatively few, despite the poor conservation status of this species and its well recognized ecological role.

Copyright © 2008 John Wiley & Sons, Ltd.     

Genetic structure of Spanish white‐clawed crayfish (Austropotamobius pallipes) populations as determined by RAPD analysis: reasons for optimism

• 1. Spanish populations of the white‐clawed crayfish have declined sharply over the last three decades. Although Austropotamobius pallipes was once widely distributed and very abundant in most of the limestone basins of the country, outbreaks of crayfish plague since 1978 have reduced its populations, and now only some 500–600 small populations are left.
• 2. Consequently, the species now enjoys protection under national legislation. Management decisions regarding the conservation of a threatened species require an understanding of the genetic structure of its populations.
• 3. Using random amplified polymorphic DNA (RAPD) fingerprinting the genetic variability of 11 populations of A. pallipes was assessed over the species' range in Spain, and their phylogenetic relationships determined.
• 4. Substantial genetic differentiation was detected among the populations tested; no clear relationship was found between patterns of genetic variability and hydrological basin. The RAPD markers showed the degree of genetic variability of these populations to be similar to, and in some cases slightly higher than, that reported in previous studies on other Spanish and European populations of A. pallipes.
• 5. The results offer hope for the recovery of this species in Spain, and provide information that might be useful in the management of crayfish reintroduction programmes.

Copyright © 2007 John Wiley & Sons, Ltd.     

Morphological diversity and phenotypic plasticity in the threatened British white‐clawed crayfish (Austropotamobius pallipes)

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Assessing the effect of size‐grading for rearing young‐of‐the‐year white‐clawed crayfish Austropotamobius pallipes

Crayfish growth rates can vary considerably among individuals from the same brood, and social dominance hierarchies in crustacean species occur frequently. These hierarchies can reduce growth and survival when rearing communal groups. Size‐grading and single‐sex culturing are the methods used to combat this. A 160‐day experiment took place on 288 young‐of‐the‐year captive‐born Austropotamobius pallipes, within a closed‐circuit, indoor aquaculture facility. Crayfish were reared in three treatments (a) equal numbers of large males + small females (LMSF); (b) equal numbers of small males + large females (SMLF); (c) individuals of the same size, equal sex ratio; plus two control groups of single‐sex, same sized individuals. Female survival in the LMSF was significantly reduced (52.8%, SD = 20.7%), whereas overall survival in all other groups was high (83.1%, SD = 15.1%). Male growth (6.3 mm, SD = 0.6 mm) was greater than female growth (4.9 mm, SD = 0.9 mm) across all groups. Cheliped autotomy was significantly greater (8.8%) in males (26.7%, SD = 8.9%) than females (17.9%, SD = 2.7%). This study suggests that young‐of‐the‐year juvenile male A. pallipes grow faster and are more aggressive than females. Large males will suppress and reduce survival in smaller females whereas small males, when housed with larger females, will still grow faster than the females. We suggest that it is sex and not size that is the main factor that causes dominance hierarchies and growth suppression within juvenile A. pallipes. Maintaining juvenile A. pallipes in single‐sex groups is optimal to ensure high survival and growth rates.     

The use of Chara spp. (Charales: Characeae) as a bioindicator of physico‐chemical habitat suitability for an endangered crayfish Austropotamobius pallipes in lentic waters

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Low genetic variability of the white‐clawed crayfish in the Iberian Peninsula: its origin and management implications

• 1. A study on the genetic variability of the white‐clawed crayfish was carried out based on mitochondrial cytochrome oxidase subunit I gene sequences. The sequences applied were more informative regarding white‐clawed crayfish genetic variability than others previously used.
• 2. Two haplotypes were found to exist in the Iberian Peninsula. The haplotypes exhibit a strong geographic subdivision (Φ_ST=0.83). One of the Iberian haplotype s was similar to north Italian haplotypes and the second differed in only one mutation. This pattern of genetic variability contrasts with those found in glacial refugial areas of France, Italy and the Balkan Peninsula.
• 3. Two hypotheses on the origin of the white‐clawed crayfish in the Iberian Peninsula are discussed: (i) one based on an anthropogenic origin, and (ii) a second based on a successive number of postglacial ancient and recent bottlenecks, i.e. the disjunction between Iberian and Italian populations of white‐clawed crayfish species is due to competition between A. italicus and A. pallipes, in addition to the impact of crayfish plague and human translocations.
• 4. New references for the white‐clawed crayfish in the Iberian Peninsula were found in medieval and Arabic texts. The results show that this species has been thriving in this peninsula since ancient periods and that its indigenous status should not be questioned.
• 5. Conservation action and plans should consider the low genetic diversity as a limitation for farm‐raising specimens more adapted and resistant to changing environments and diseases.

Copyright © 2007 John Wiley & Sons, Ltd.     

Incisor ridge modification of the mandibles in freshwater crayfish, Astacus leptodactylus

The differences in the ridge structure of the mandibles of different size Astacus leptodactylus (32–80 mm carapace length, CL) were investigated. The results showed that a modification occurs with an increase in size in the incisor ridge of mandibles in A. leptodactylus. The results also showed that A. leptodactylus possesses four different types of ridge structure in the mandibles. These are: (1) Incisor ridge with big teeth (dentate crenate), (2) Blade-like incisor ridge with numerous small teeth, (3) Blade-like ridge (toothless), (4) Blunt ridge. In conclusion, it is thought that the incisor ridge modification of the mandibles may cause the difference in the food choice of different size A. leptodactylus, because, crayfish possessing different ridge structures of the mandible may probably feed on different type of food.     

Decapsulated Artemia cysts as dietary supplement for juvenile crayfish (Pacifastacus leniusculus, Astacidae) at different food supply frequencies from the onset of exogenous feeding under controlled conditions

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.     

克氏原螯虾染色体及其核型

染色体是遗传物质的载体,是研究细胞遗传学的基础,为研究克氏原螯虾染色体及其核型,实验以性未成熟雄性个体的精巢为材料,采用低渗和空气干燥常规方法制备细胞分裂中期染色体标本,研究了克氏原螯虾染色体及核型。Giemsa和DAPI染色后在显微镜下观察到清晰的精母细胞减数分裂中期二价体和精原细胞有丝分裂中期染色体时相。对减数分裂中期二价体及有丝分裂中期染色体进行了数目上的统计。结果显示,克氏原螯虾二倍与单倍染色体数目分别为2N=188和N=94。由于有丝分裂染色体形状微小,核型分析困难,故选取减数分裂中期二价体,根据长度及着丝点位置对其进行了初步核型分析,核型公式为N=55M+22(SM,ST)+17T,未发现异形性染色体。     

Abundance and production of the introduced signal crayfish ina British lowland river

In 1984, 40 mature and 100 immature signal crayfish, Pacifastacus leniusculus (Dana), were introduced into the River Great Ouse, England. By 1994, the population had spread up and down stream to occupy an 11.4 km river section. The estimated density and biomass (wet weight) of the population in 1993 were highest in summer at 4.0 m^–2 and 133 g m^–2 respectively, with annual means of 2.2 m^–2 and 82 g m^–2 for crayfish of >30 mm carapace length (CL) in the pool (P2) where the crayfish were originally introduced. Density and biomass were 15 m^–2 and 78 g m^–2, with annual means of 6.1 m^–2 and 33 g m^–2 for crayfish of all sizes in a riffle 300 m downstream from P2. An annual survival rate of 14% was estimated for crayfish >30 mm CL in P2 in 1993. The relative abundance estimated for six riffles and six pools in 1994 showed that crayfish abundance decreased gradually from the original site of introduction both up and down the river. Estimated annual production of crayfish >35 mm CL in P2 for 1993 was 52.58 g m^–2 WW, with a turnover ratio (production/biomass) of 0.44.     

Effects of breeder reuse on the reproductive potential of the signal crayfish (<Emphasis Type="Italic">Pacifastacus leniusculus</Emphasis> Dana. Astacidae) in culture

The aim of this work was to evaluate the reproductive potential of the signal crayfish (Pacifastacus leniusculus Dana) in the second cycle under culture conditions. The experiment was carried out using 5,653 animals placed in six earthen ponds in August. Three treatments were performed, each in two ponds: breeder reuse (males and females used in the former reproductive cycle), female reuse (new males from the wild and females used in the former reproductive cycle) and new breeders (males and females from the wild). In April, close to hatching, egg-bearing females were transferred to the hatchery. Mortality of the reused breeders (around 30% of females and 41.4% of males) was significantly higher than that of the new breeders (11.4% of females and around 19.5% of males). The proportion of berried females close to hatching was significantly higher for the new ones (77.4% of the initial number), and the percentage of new females with a large quantity of eggs (63.6%) was higher than that of the reused females (25.6 and 20.9%). Differences among the percentages of females without eggs in the new breeders (11.2%) and the rest of the treatments (30.7 and 39.6%) were significant. The reproductive capacity of reused females was not improved by providing new males. Considering the number of females initially stocked into ponds, mean yield per new female was greater than that of the reused females, mainly due to the higher mortality recorded in the reused broodstock. Although the yield that can be obtained using the same breeders in two reproductive cycles drops in the second one, the production was not negligible.     

Effects of different bronopol treatments on final survival rates in the artificial incubation of crayfish eggs (Pacifastacus leniusculus,Astacidae)

Two experiments were conducted on the effects of bronopol in the artificial incubation of crayfish eggs (Pacifastacus leniusculus) with the aim to search an alternative to formaldehyde. In the first experiment, 50, 250, 500 and 1000 ppm bronopol and 3000 ppm formaldehyde (control) in periodical administrations were tested on a density of 6.6 eggs cm^?2. After 44 days of incubation, the highest survival was obtained with 1000 ppm bronopol (81.9% to stage 2 juvenile, with no significant difference from formaldehyde), whereas lower bronopol concentrations resulted in significantly lower survival. In the second experiment, 1000, 3000 and 5000 ppm bronopol and 3000 ppm formaldehyde (control) administered for 15 min every second day were tested on eggs at a density of 20 eggs cm^?2. After 78 days of incubation, bronopol at 3000 ppm allowed for a stage 2 juvenile survival rate of 65.0% (with no significant difference from formaldehyde), whereas significantly lower survival was obtained with 1000 ppm or 5000 ppm. This study shows that bronopol may constitute an alternative to formaldehyde in the artificial incubation of crayfish eggs. A concentration of 3000 ppm administered for 15 min every second day may be adequate even on long incubations at high densities (at least 20 eggs cm^?2, one complete layer).