1. The white-clawed crayfish, Austropotamobius pallipes (Lereboullet), is the only freshwater crayfish indigenous to Great Britain and Ireland. It has a widespread, though declining distribution in England and parts of Wales but does not occur naturally in Scotland. 2. The North American signal crayfish, Pacifastacus leniusculus (Dana), is not native to Europe and was introduced to Britain in the 1970s. The signal crayfish out-competes the native white-clawed crayfish as it is larger and more aggressive. It is also responsible for the introduction and spread of crayfish plague, which has devastated white-clawed crayfish populations in Europe. 3. Signal crayfish populations are causing significant changes to the equilibrium of native flora and fauna through increased grazing and predation pressures; they also contribute to habitat degradation through burrowing. 4. Manual removal of crayfish using traps and pond trials with biocides have met with moderate success in reducing crayfish numbers and containing populations. However, with new populations of signal crayfish being reported each year within the UK, there is now an urgent need to develop a strategy with which to eradicate or contain their spread. 5. Signal crayfish have populated many habitat types in the UK, each of which may require a different control strategy; hence no single strategy or universal solution is likely to be attainable. 6. Signal crayfish are susceptible to various biocides and microbial pathogens but significant scientific research will be required to develop safe biological control methods and integrated pest management (IPM) strategies to control these invasive organisms

ABSTRACT1. The effect of a newly introduced population of signal crayfish (Pacifastacus leniusculus) on a riverine invertebrate community in the River Clyde, Scotland, is examined. Five hypotheses related to crayfish impact on the invertebrate community are tested by comparing sites containing signal crayfish with similar sites in the same river which have not yet been colonized.2. The hypothesis that crayfish significantly reduce the total numbers of invertebrates in the community was supported by this study, with invertebrate density in areas containing signal crayfish around 60% of that with no observed crayfish.3. The hypothesis that crayfish presence affects some groups more than others was also supported. Plecoptera, Chironomidae, Diptera and Hirudinea, in particular, showed evidence of reduced species numbers in areas containing crayfish, and Plecoptera, Hirudinea, Tricladida and Hydracarina showed evidence of reduced densities. Community diversity and richness was also lower at sites containing crayfish.4. Neither the hypothesis that overall invertebrate biomass would be lower at sites with crayfish present nor the hypothesis that individual invertebrate size would be lower at sites with crayfish was supported.5. Overall the study indicates that introduced signal crayfish can significantly and fundamentally modify fluvial macroinvertebrate community structure.

Eriocheir sinensis, the Chinese mitten crab, is a native of east Asia and predominantly lives in freshwater but migrates seawards to breed. In 1912 a specimen was collected in the River Aller, a tributary of the Weser, Germany and now this exotic species has a European distribution from Finland to the Atlantic coast of southern France. In the UK, the mitten crab has been reported from the Humber, Medway and Thames catchments. Although the population in Thames had remained low, recent evidence suggests it is increasing, which has potential environmental implications.

15394-46914 2 Indicators of a generalised stress response (changes in cortisol, glucose, RNA:DNA ratio and total protein) when measured in whole-body preparations of individual sticklebacks display significant alterations in response to acute (hours) and chronic (days) disturbances and food withdrawal. In addition, changes in alkali-labile phosphorous, a specific biomarker of exposure to estrogenic contaminants, can be detected in whole-body preparations of estrogen-exposed sticklebacks confirming that the measurement of biomarkers normally assessed in a specific tissue can be equally possible in whole fish.

The NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. ABSTRACTIn contrast to the relatively minor intra-and inter-species differences in blood cortisol levels reported for salmonid species, there is a more pronounced distinction between cortisol levels among the Salmonidae and Cyprinidae, with both basal and stressinduced cortisol levels markedly higher in the latter. This study shows that in the chub, Leuciscus cephalus, a widely distributed European cyprinid, mean blood cortisol levels during stress (1500 ng ml -1 ) exceeded those reported for most other species of fish and even in unstressed chub, cortisol levels (50 -100 ng ml -1 ) were within the range known to cause immunosuppression, growth retardation and reproductive dysfunction in salmonid fish. The chub appears to be atypical only with respect to plasma cortisol levels; the levels of plasma glucose and plasma lactate in unstressed and stressed chub are similar to those reported for other species. Plasma levels of 11-ketotestosterone in males and 17-estradiol in females are lower than reported for salmonids but similar to other cyprinid species and display clear stressinduced reduction. Comparative analysis of the binding characteristics of the trout and chub gill cortisol receptor revealed that the total number of binding sites in gill tissue for each species was similar (Bmax; ~50 -100 fmol mg -1 protein). However, the affinity of the binding site for cortisol displayed an 8-fold difference between the species (rainbow trout: Kd ~ 6 nM; chub: Kd ~ 50 nM). Therefore, the potentially adverse effects of high circulating levels of cortisol found both at rest and under conditions of stress in chub may be offset by the lower affinity of the cortisol receptor, rather than the abundance of target-tissue receptor sites. This strategy is similar to that reported for some glucocorticoid-resistant rodent species and New World primates.3