Native European freshwater crayfish (Astacida, Decapoda) are under severe pressure from habitat alteration, the introduction of nonindigenous species, and epizootic disease. Crayfish plague, an acute disease of freshwater crayfish caused by the fungus-like agent Aphanomyces astaci, was introduced into Europe in the mid-nineteenth century and is responsible for ongoing widespread epizootic mortality in native European populations. We reviewed recent developments and current practices in the field of crayfish pathology. The severity of crayfish plague has resulted in an overemphasis on it. Diagnostic methods for detecting fungi and fungal-like agents, and sometimes culturing them, are frequently the sole techniques used to investigate disease outbreaks in European freshwater crayfish. Consequently, the causes of a significant proportion of outbreaks are undetermined. Pathogen groups well known for causing disease in other crustaceans, such as viruses and rickettsia-like organisms, are poorly understood or unknown in European freshwater crayfish. Moreover, the pathogenic significance of some long-known pathogens of European freshwater crayfish remains obscure. For effective management of this culturally significant and threatened resource, there is an urgent need for researchers, diagnosticians, and resource managers to address the issue of disease in European freshwater crayfish from a broader perspective than has been applied previously. Entendiendo las Causas de Enfermedad en Cangrejos Europeos de Agua DulceResumen: Los langostinos nativos de Europa (Astacida, Decapada) están bajo severa presión por alteración del hábitat, la introducción de especies no nativas y una enfermedad epizoótica. La peste de langostinos, una enfermedad aguda de langostinos de agua dulce producida por el agente micoide Aphanomyces astaci, fue introducida a Europa a mediados del siglo diecinueve y es responsable de la actual mortalidad epizoótica de poblaciones Europeas nativas. Revisamos acontecimientos recientes y prácticas actuales en el campo de la patología de langostinos. La severidad de la peste de langostinos ha resultado en un excesivoénfasis en ella. Los métodos para diagnosticar, y algunas veces cultivar, hongos y agentes micoides frecuentemente son laúnica técnica empleada al investigar brotes de la enfermedad en langostinos de agua dulce en Europa. Consecuentemente, no están determinadas las causas de una proporción significativa de los brotes. Grupos patógenos, como virus y organismos similares a rickettsias, bien conocidos por producir enfermedades en

Growth, mortality, moulting rate and cheliped loss were examined in aquaculture experiments with noble crayfish, Astacus astacus L., juveniles from four different Norwegian populations in the period September 1987‐June 1988. The juveniles were hatched indoors in May 1987 from parents wild‐caught in 1986. The experiments were performed at 18‐19°C in communal rearing units. Mean total length at experiment start was about 20mm in all groups. There were no significant differences in mean size (final mean total length: 32‐2‐34‐8mm). mortality (83a‐900%) or cheliped loss (429‐700%) among juveniles from the different populations when exposed to similar conditions (food: dry pellets; photoperiod: L:D = 8:16). Among crayfish fed fish and potatoes in addition to dry pellets, and with continuous light conditions, mortality was reduced significantly to about 70%. Continuous light conditions significantly increased mean size (final mean length: 36‐1‐389mm). Moulting occurred from November throughout the experiment period. Moulting rate was positively correlated to mortality and growth rate (i.e. mean length increase). A positive correlation between mortality and cheliped loss, along with direct observations of cannibalism, indicated that agonistic behaviour and cannibalism were the dominating mortality factors. It is suggested that continuous light conditions reduce agonistic behaviour and thereby decrease mortality.

No abstract

The noble crayfish, Astacus astacus, is highly valued from a recreational and economical point of view. In most noble crayfish areas, there are long traditions of crayfish catching. The noble crayfish is also included in national and international Red Lists as a vulnerable or threatened species. Intuitively, the first thought is that such a species should be protected from exploitation. However, in many cases the possibility for exploitation and local economic benefits may be important for the conservation of the species. For the noble crayfish this is especially true. The greatest threat against noble crayfish is the man-facilitated spread of plague-carrying alien crayfish species. If local people are allowed and encouraged to catch and make a benefit from noble crayfish, this is also the best protection against illegal stocking of alien crayfish. The possibility to exploit the crayfish is of major importance for the will to protect. Examples from Norway showing different ways of getting an economical and recreational outcome from the noble crayfish are presented.

No abstract

No abstract

No abstract

Abstract. The noble crayfish, Astacus astacus L., is extensively used for stocking and restocking purposes both in Scandinavia and in other European countries. It also has potential as a farmed species. Thus, it is important to have information about the genetic structuring of the species. Attempts have been made to detect genetic variability in A. astacus and find markers suitable for interpopulation discrimination. Two loci, coding for the enzymes leucine‐aminopeptidase (LAP) and xanthine dehydrogenase (XDH), have previously been found to exhibit allele frequency differences among four recently established populations of crayfish in southern Norway. Eight more populations have now been studied for these and 13 other enzyme‐coding loci. All of the 13 additional loci examined were found to be monomorphic. The variable zymogram bands of LAP and XDH are thought to reflect genetic variation at their encoding loci. It is suggested that the significant inter‐stock allele frequency differences at these loci are to a large extent due to founder events and random genetic drift. Since information about the size and genetic characteristics of the founder populations is limited, the relative contribution of selective constraints to stock diversity cannot be assessed. For restocking strategies one should consider using both reserve populations of the original populations and other strong populations with known genetic characteristics.