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.     

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.     

Spatial ecology of the white‐clawed crayfish in an upland stream and implications for the conservation of this endangered species

• 1. Populations of white‐clawed crayfish (Austropotamobius pallipes) have undergone substantial declines across Europe. Remaining populations tend to be fragmented and in many catchments they are restricted to upland streams. Information is needed concerning their spatial ecology to assist with conservation and rehabilitation of existing fragmented populations, as well as possible reintroductions.
• 2. A novel method for the long‐term tagging of white‐clawed crayfish was used to study the spatial ecology of a white‐clawed crayfish population fragment in a small, moderate‐gradient upland stream. Internal passive integrated transponder (PIT) tags enabled adult crayfish (carapace length >27 mm) to be permanently tagged, each with a unique identification code and resulted in a high number of recaptures. Of 501 crayfish tagged 413 were subsequently relocated at least once.
• 3. Crayfish did not make extensive movements, the median annual distance moved was 84.8 m yr^?1, equivalent to annual net movement of 0.233 m day^?1, substantially less than reported in previous studies. The lower levels of movement may reflect the study encompassing all seasons, including winter, when crayfish are relatively inactive.
• 4. Significantly more crayfish moved downstream compared with upstream and distances moved downstream were significantly greater than those in an upstream direction. This may be linked to the relatively high gradient of the stream and a reduced passability of the abundant riffles to upstream movements of crayfish.
• 5. A small weir acted as a barrier within the stream, preventing upstream movements of crayfish. Even small barriers may limit the movements of white‐clawed crayfish and have the potential to limit connectivity within populations and prevent expansion or recolonization.
• 6. The results presented suggest that fragmented populations of white‐clawed crayfish in upland streams are unlikely to expand rapidly and reconnect to other population fragments, even where habitat is suitable. In establishing stream populations care should be taken to ensure that even small barriers to movement are removed unless these are intended to exclude non‐native biota, especially crayfish.

Copyright © 2007 John Wiley & Sons, Ltd.     

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.     

Genetic diversity of Nile tilapia populations revealed by randomly amplified polymorphic DNA (RAPD)

Genetic diversity of the Nile tilapia Oreochromis niloticus collected from the river Nile (Cairo, Assuit and Qena) and two Delta lakes (Burullus and Manzalla) in Egypt was examined by the analysis of randomly amplified polymorphic DNA (RAPD). Of 25 primers examined,21 primers produced 230 RAPD bands. The percentage of polymorphic bands in Manzalla (29.4%) and Burullus (24%) populations was low compared with Assuit (30.54%), Cairo (33.5%) and Qena (44.84%) populations. The highest percentage of polymorphic bands was observed in the Qena population,suggesting a greater potential for use in breeding programs. The molecular phylogenetic tree constructed by unweighted pair‐group method of analysis shows Manzalla and Burullus populations strongly linked and separate from the Assuit and Cairo populations, with Qena population as outgroup. The data serve as a baseline analysis of the current genetic diversity found among O. niloticus populations in Egypt.     

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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The genetic structure of Mytilus chilensis (Hupé 1854) populations along the Chilean coast based on RAPDs analysis

The Chilean blue mussel Mytilus chilensis is an important commercial species. However, little has been published on the population genetics of this species, despite the need to implement management and conservation policies. Randomly amplified polymorphic DNA‐polymerase chain reaction analysis was used to estimate genetic variation within and between eight natural populations along the whole range of its Chilean natural distribution (ca. 1900 km from Arauco (VIII Region) to Punta Arenas (XII Region)). The values of Nei's unbiased genetic distance, D (0.030–0.107), among populations were small, despite the large geographic separation. A mantel test using 50 000 randomizations showed evidence for a significant correlation (r=0.74, P<0.05) between genetic and geographic (coastal) distance. Punta Arenas population was the most genetically differentiated from the others, although the scale of differentiation was not large (D=0.076–0.107). The levels of gene flow (Nm=1.55) found in this study prevent differentiation among populations by genetic drift. This is the result of the long‐lived planktotrophic larvae of M. chilensis, which provides this species with considerable dispersal ability throughout its range, which is favoured by the ocean currents along the Chilean coast. A restricted larval dispersal towards the north due to the Cape Horn Current derived from the West Wind Drift could be the cause of the higher genetic differentiation of Punta Arenas population from the northern populations. For management purposes of the M. chilensis fishery, the results provide no evidence for discrete stocks, with the possible exception of the Punta Arenas population. The present study provides the baseline data in order to continue further characterization of these mussel populations, considering the great increase in aquaculture of this species.     

Assessment of genetic structure,habitat suitability and effectiveness of reserves for future conservation planning of the Euphrates soft‐shelled turtle Rafetus euphraticus (Daudin, 1802)

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Genetic assessment of milkfish (Chanos chanos Forsskal) stocks based on novel short tandem repeats for marker‐aided broodstock management

Milkfish hatchery broodstock are either from on‐grown wild‐caught or hatchery‐produced fry/juveniles. To determine if a marker‐assisted management scheme can be formulated for improved milkfish hatchery production, milkfish stocks were genetically characterized using nine novel short tandem repeats or microsatellites. Eight wild‐bred Philippine stocks (CLA, CUR, CAM, SIH, SBH‐I1, HH, PAL and ZH‐P₀), four hatchery‐bred stocks (SBH‐I2, SBH‐D, BoH and ZH‐F₁), two farm stocks of known mixed lineages (SPH and BDH) and one Indonesian hatchery‐bred stock (WJH) were assessed. WJH was included since milkfish fingerlings from Indonesia reared in Philippine farms could be developed into future broodstock. Mean allelic richness (Ar) was highest in wild‐bred stocks (9.5) and lowest in hatchery‐bred spawners (9.1). Mean expected heterozygosities (He) were relatively similar in all stocks with wild‐bred stocks slightly higher (0.67) than the others. An analysis of molecular variance indicated significant yet low genetic differentiation among stocks (F_ST = 0.013; p = .000) where variation (98.6%) was explained by intra‐stock differences. In some of the domesticated stocks, reductions in mean allelic richness were observed in first generation hatchery broodstock (e.g. ZH‐F₁; Ar = 8.3), compared with their founder stock (e.g. ZH‐P₀; Ar = 9.4). The Indonesian stock was similar to local wild‐bred stocks based on genetic variability indices; thus, it might be likely that the local stocks’ fitness traits could be comparable with the imported milkfish stock which has been perceived to be better. The quality of locally available farmed milkfish and prospects of formulating a broodstock management scheme for the production of good quality milkfish seedstock are herewith discussed.     

Investigating the genetic structure of trout from the Garden of Ninfa (central Italy): Suggestions for conservation and management

Mediterranean populations of brown trout (Salmo trutta L. complex) have lost a large part of their genetic distinctiveness, mostly due to massive restocking, and the waters of the Gardens of Ninfa (province of Latina, central Italy, Site of Community Importance since 2013) are regarded as one of a few potential reservoirs of autochthonous trout lineages in the Tyrrhenian drainage of the Italian peninsula. In this study, nuclear and mitochondrial markers were used on brown trout samples from Ninfa to estimate non‐Mediterranean influence in the population gene pool, potential changes of genetic structure over time and genetic relationships with other sites known (or suspected) to host native trout gene pools. Striking changes in both microsatellite and mtDNA allele frequencies over a 9‐year time span were found and provided evidence of unrecorded stocking from the nearby Lake Fibreno. Results are analysed in the light of potential ecological consequences of such events on a longer time scale and provide a scientific background for fisheries management and conservation programmes in the area.     

Genetic diversity and structure of Northern Sheatfish (Silurus soldatovi) assessed by newly developed and cross‐species microsatellites

Twenty‐five polymorphic microsatellite markers, including 13 newly isolated markers and 12 existing cross‐species markers, were used to assess the genetic variation of 141 individuals from three cultured stocks of northern sheatfish, Silurus soldatovi, in China. Samples were collected from Heilongjiang (H), Tongerpu (T) and Liaoning (L). Allelic richness, expected and observed heterozygosity among 25 loci were calculated, and the mean A_e, H_o and H_e were estimated in three stocks. In low polymorphic locus HLJcf19 and HLJcf38, most individuals in all three stocks were homozygous and had only one same allele, while only few heterozygous individuals had the other allele in one certain stock. And all the three stocks showed excess of heterozygotes, because of significant negative F_IS values. Genetic distance, UPGMA dendrogram, as well as structure analysis, all indicated that Stock H and L were closer among three stocks. The results revealed that though all stocks had no reduction in recent time, their effective population size were significantly lower to the ideal value.     

Validation of environmental DNA (eDNA) as a detection tool for at‐risk freshwater pearly mussel species (Bivalvia: Unionidae)

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Genetic monitoring of deep‐water exploited banks of the precious Sardinia coral Corallium rubrum (L., 1758): useful data for a sustainable management

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