David M. Holdich

Nonindigenous Crayfishes Threaten North American Freshwater Biodiversity: Lessons from Europe

Abstract North America harbors about 390 native species of crayfishes, 75% of the worlds total. In this article, we highlight the threats posed by nonindigenous crayfishes to freshwater ecosystem function, fisheries, and the biodiversity of native crayfishes; draw some lessons for North American freshwater conservation from the experience with nonindigenous crayfishes in Europe; and review existing regulations that address the introduction of nonindigenous crayfishes. Most North American crayfishes have naturally small ranges in the southeastern United States, rendering them very vulnerable to environmental change. In contrast, Europe has only five, broadly distributed, native crayfishes, all of which have been greatly affected by environmental changes, especially the introduction of nonindigenous crayfishes (mostly from North America). In response, many European governments have adopted strict regulations to protect native crayfishes. The loss of thousands of populations of native European crayfishes an...

Signal crayfish as vectors in crayfish plague in Britain

Abstract 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.

On size and sexual dimorphism in Austropotamobius pallipes (Lereboullet): A step in assessing the commercial exploitation potential of the native British freshwater crayfish

Abstract Interest in crayfish farming in Great Britain is currently very high. Attention is drawn in this paper to the naturally occurring British crayfish resource. The unexploited native crayfish Austropotamobius pallipes is examined with respect to size and sexual dimorphism of the chelipeds and abdomen, with a view to aiding assessment of the possible commercial potential of this species. Individuals can be designated mature or immature regarding production potential on the basis of a sudden increase in the size of the chelipeds at 29.0 and 30.7 mm carapace length for males and females, respectively. A disproportionate increase in abdomen width is also recorded for females at the 24.0 mm carapace length stage. This probably represents the onset of sexual maturity. The importance of a consideration of reproductive efficiency in a cropping strategy is emphasised. Conclusions can thus be drawn as to the acceptability of the size of the British crayfish, which is present in large populations in some areas. An attempt has been made to provide quantitative guidelines as to expected size, and a size above which crayfish may be more productively cropped is also suggested. On the basis of current data, this species appears to be at no major disadvantage with regard to these size parameters when compared with other crayfish species being marketed.

Length-weight relationship, muscle production and proximate composition of the freshwater crayfish Austropotamobius pallipes (Lereboullet)

Abstract Significant sexual divergence in weight occurred in a sample of 276 crayfish at body lengths greater than 60 mm. Males reached approximately 60 g and females approximately 35 g wet weight. Immature males and females did not differ significantly in weight. Abdominal muscle in larger specimens attained a maximum weight of 3.53 g and 3.78 g in males and females, respectively. Percentage contribution by abdominal muscle to total body weight was 14.43 ± 2.59% ( N = 40) for males and 15.73 ± 2.16% ( N = 40) for females. Up to 5.13 g of cheliped meat was produced by males but females only produced up to 2.52 g. This difference was largely responsible for the significant differences in total muscle weight expressed as a percentage of body weight between males (27.38 ± 2.36%, N = 40) and females (23.21 ± 2.08%, N = 40). However, male muscle contained significantly more water than female muscle. A new analytical scheme developed to assess crayfish muscle composition revealed a relatively low protein and high lipid content in A. pallipes but other tissue component levels were similar to those of three other marketed crayfish species.

2,3,7,8-tetrachloro-dibenzo-p-dioxin is a potent toxin and induces cytochrome P450 in the crayfish, Pacifastacus leniusculus

Abstract 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) is the most potent congener of a family of environmental contaminants. We demonstrate that TCDD is a highly potent toxin in an invertebrate, the freshwater crayfish, Pacifastacus leniusculus, with an LD50 of 30–100 μg kg−1 of body weight. Toxicity was characterised by delayed mortality, typically 15–40 days after dosing, and anergia. No gross histological changes were seen in hepatopancreas. Treatment of crayfish with 3 μg of TCDD kg−1 body weight significantly induced cytochrome P450, as measured spectrally, but we were unable to measure associated enzyme activities, presumably due to proteolysis of NADPH-P450 reductase. TCDD is thus a potent toxin and enzyme inducer in crayfish. We hypothesise that the nature of this pleiotropic response, together with its exceptional potency, suggests the presence of a receptor-mediated mechanism of TCDD toxicity in crayfish.

Cryptic diversity within the invasive virile crayfish Orconectes virilis (Hagen, 1870) species complex: new lineages recorded in both native and introduced ranges

The virile crayfish (Orconectes virilis) represents a cryptic species complex with several lineages known in the USA, and a wide introduced range. In Europe, O. virilis is an emerging invader, established during the last decade in at least two areas—one in the United Kingdom and another in the Netherlands. We assessed the position of both known European populations within the species complex by sequencing part of the mitochondrial gene for cytochrome c oxidase subunit I. Tested UK and Dutch individuals did not belong to any mitochondrial lineage recorded in North America so far but formed a separate clade, the original distribution area of which is unknown. Additionally sequenced virile crayfish from Iowa (USA) also represented a new clade, suggesting that undiscovered lineage variation within O. virilis remains high. This exemplifies that genetic analyses of invading populations may provide new insights into diversity of a taxon in its original range.

Changes in osmotic pressure and sodium concentration of the haemolymph of woodlice with progressive desiccation

Abstract 1. 1. Haemolymph osmotic pressure was measured in four species of woodlouse after pre-treatment in 100% R.H. followed by progressive desiccation. 2. 2. Considering sexes together it was found that Oniscus asellus cannot osmoregulate but that Porcellio scaber and Armadillidium depressum can. Ligia oceanica showed a greater osmoregulatory ability during aerial desiccation than some other “more terrestrial” species. All species except A. depressum showed considerable sexual variation in their response to desiccation even though the pre-treatment values were similar. 3. 3. Sodium levels were monitored with progressive desiccation in O. asellus and P. scaher. Contrary to expectation the former species showed greater sodium control than the latter.

Crayfish in the British Isles

Abstract The distribution, breeding biology, diseases, and ecology of the native British freshwater crayfish species are reviewed in the light of the current upsurge in interest in crayfish culture. The introduction into the British Isles of alien species is discussed with particular reference to the effect which they might have on native populations. The possibility of cropping large populations of the native crayfish is outlined.

The effect of water quality on the size and fecundity of Asellus aquaticus (Crustacea:Isopoda)

Abstract Samples of Asellus aquaticus (L.) were collected from a number of freshwater sites in central England exhibiting either clean, semi-polluted or polluted conditions. The clean sites contained naturally decaying organic matter but the polluted sites also contained sewage and toxicants. The asellids were found to vary in the maximum length attained, and in pereonal width and fresh body weight, in response to water quality. In asellids from polluted sites the body size (length × average pereonal width) and wet weight were significantly lower than those from a clean site. Asellids free semipolluted sites showed an intermediate condition. The number of eggs contained in the marsupia of ovigerous females increases witn body size. However, the actual number of eggs is dependent upon the water quality, there being more eggs in the marsupia of all sizes of ovigerous females from clean sites than those from polluted sites. Asellids from semi-polluted sites showed an intermediate condition. Ovigerous females from polluted sites, kept in clean water, produced F 1 generations which, when grown in clean water, showed a significant increase in body size and weight. f 1 generation males, derived from clean water females and grown up in clean or polluted water at 20°C, showed a significantly larger increase in width for any given body length in clean water than they did in polluted water. Care must therefore be taken when comparing growth rates of animals from different geographical locations which exhibit different degrees of water quality.

Water exchange between woodlice and moist environments, with particular reference to Oniscus asellus

Abstract 1. 1. Measurements of water flux in certain terrestrial isopods, especially Oniscus asellus , using tritiated water and weighing techniques, indicates that water exchange occurs between the animals and a variety of moist environments. The flux rate is different species, and varies, in O. asellus , with actual moisture condition. 2. 2. The order, in terms of decreasing magnitude of the influx of tritiated water, is: Ligia oceanica > O. asellus > Porcellio scaber > Armadillidium vulgare . 3. 3. O. asellus appears to be in equilibrium with moist conditions providing it is not immersed. 4. 4. The relevance of these results to the behaviour and physiology of woodlice is discussed.