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

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An organism tentatively classified as Psorospermium haeckeli was found in red swamp crayfish Procambarus clarkii at four culture sites in southwestern (3) and southeastern Louisiana (1) and in white river crayfish Procambarus zonangulus (=P. acutus acutus) at three culture sites in southwestern Louisiana. Incidence was about 70% in P. clarkii and 25% in P. zonangulus. Psorospermium haeckeli was present in all individual populations of P. clarkii sampled, but not in all P. zonangulus populations. Overall abundance was considerably lower than that observed in the European astacid crayfish Astacus astacus. Furthermore, the organism differed in shape, being longer and narrower than the organism found in A. astacus.

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Migration of Hg from black shales to the aquatic ecosystems and local residents was studied comprehensively with samples of black shales (627 samples), surface waters (22), organic stream sediments (40), organic lake sediments (172), noble crayfish (72) and human hair (225). The black shales exhibited elevated C, S, Ni, Cu, Zn, Cd and Hg concentrations. Gneiss granite, mica schist, and quartzite with very low heavy metal contents are encountered just next to the black shales, offering good reference areas for comparison. There are no local anthropogenic Hg sources in the study areas. Black shale areas were reflected as elevated Ni, Cu, Zn and Cd and low Ca in glacial till, surface waters, organic stream sediments and lake sediments. Mercury behaved differently in surface waters than the other heavy metals: there was no correlation between the Hg concentration of the surface waters and the Hg concentration of the underlying bedrock. Median values for total Hg and methyl-Hg in stream water were 1.6 and 0.2 ng/l, respectively, in the black shale area, and 2.0 and 0.3 ng/l in the adjacent reference area with Hg-poor bedrock. Even though Hg concentrations in surface waters were not elevated in the black shale areas relative to the reference areas, mean Hg concentrations of the muscle of noble crayfish (Astacus astacus) were higher in black shale area lakes than in lakes in the reference areas. The explanation of this correlation probably is not Hg flux from the bedrock to watercourses. As a more easily eroded rock than granites, quartzites, and mica schists, black shale tends to occur in topographic depressions in glaciated terrain. Lakes in the black shale areas are typically surrounded by peatlands, and the catchment areas, from which they collect humic material rich in Hg, may be extensive. The total Hg concentrations in hair ranged from 0.04 to 12.1 lg/g. The distribution of hair Hg content did not appear to correlate with the distribution of black shales. In the present study, the main route of Hg to humans was via fish. Even though Hg contents were higher in crayfish and fish in the black-shale-area lakes, people consumed fish not only from the lakes next to their residence, but also from lakes situated in the reference areas. Among the non-fish-eaters in one black shale area, the use of dug well water, as well as the consumption of local potatoes and mushrooms, slightly increased the Hg in hair. This contribution may reflect the heavy metal load of the natural black shale environment.