Aphanomyces astaci is a member of a group of organisms commonly Aphanomyces astaci, both in culture and in infected crayfish, is killed by. Aphanomyces astaci commonly referred to as crayfish plague is an oomycete or water mould that infects only crayfish species. It is endemic of. The pathogen Aphanomyces astaci Schikora is responsible for the decline of the native crayfish species of Europe, and their current.
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In contrast, in North American crayfish species, Astai. Since then it has spread across large parts of Europe, leading to several outbreaks of crayfish plague in European crayfish populations and being considered the most important reason for the decline of these species across Europe. The source of the original infections in the 19th century was never established; but the posts spread is largely linked to the introduction and spread of North American crayfish introduced for purposes of crayfish aphanomyyces.
The natural range of A. Any occurrence of A.
Prevalence of the pathogen Aphanomyces astaci in freshwater crayfish populations in Croatia.
The first evidence for the arrival of A. These were followed by further reports of crayfish mortalities, where no other aquatic species were affected, in the Franco-German border region in the third quarter of the 19th century. From there a steady spread of infection occurred, principally in two directions: In the s, the first outbreaks were reported in Spain and in the s the disease spread further to the British Isles, Turkey, Greece and Norway Alderman, The source of the original infections in the 19th century was never established.
The spread of the disease posts is largely linked to introductions of North American crayfish for crayfish farming Alderman, Pacifastacus leniusculusOrconectes limosus and Procambarus clarkii are now widely naturalised in many parts of Europe.
Since North American crayfish serve as a reservoir of A. Some North American crayfish species, such as Procambarus clarkiihave been introduced for aquaculture purposes into many areas around the globe, like Central America, South America, Europe, Africa, China and other parts of east and south Asia. In most cases where P. It is not known whether all of these populations would still be carriers of A. The actual distribution of A. If there are no susceptible species in the area to which the North American crayfish are introduced, there may be no impact of such introductions associated with A.
Details for introductions of North American crayfish species into new geographic areas can be obtained from Gherardi and Holdich The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status.
Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report. The early history of the introduction of Aphanomyces astaci into areas outside of its natural range in North America is based on cases of large mortalities of European crayfish species, which appeared to be associated with a pathogen, rather than pollution incidents. Initially, it was thought that the disease was caused by a bacterium, Bacillus pestis astaci Hofer, However, in Schikora identified a fungus, an Aphanomyces species, as the disease agent.
Prevalence of the pathogen Aphanomyces astaci in freshwater crayfish populations in Croatia.
It was not until that A. Therefore, what are described as the early cases of crayfish plague in Europe are based on observations of large-scale mortalities of European crayfish species that appeared to be the result of a highly virulent pathogen.
Cultivation methods were accompanied by several problems, and it was difficult to obtain A. With the development of molecular methods for the diagnosis of crayfish plague, the pathogen has been diagnosed more frequently. Based on circumstantial evidence, it is thought that the first likely introduction of A.
The next cases of crayfish plague appeared in on the Plateau de Langres, which is located in central-eastern France Raveret-Wattel, ; Vivier, The outbreaks in France seem to have been the source for the further spread of the disease across Europe in the following decades. From France, the disease seems to have spread to neighbouring Germany inand from Germany to Austria in and Switzerland in In the following decades, the pathogen reached eastern Europe Poland, ; Slovenia, ; Latvia ; Russiaand Scandinavia Finland inSweden in The early outbreaks of the disease were probably associated with the movement of infected European crayfish or movement of A.
Crayfish plague was reported from new geographical areas again in the s, when it was reported for the first time from Spain. In principle, spread of crayfish plague can be through 3 pathways: Spread independent of crayfish host tissue can be through contaminated water, and mechanical vectors or fomites that have been in contact with contaminated water.
The mechanical spread route is more relevant for relatively short durations of transfer due to the limited survival of the pathogen outside a crayfish host.
Examples of fomites that may be involved in mechanical transmission are: Fish themselves may also serve as vectors in several ways: However, it still remains to be shown that transmission via fish skin occurs in vivo Oidtmann et al. Mechanical spread would be most relevant from sites of current crayfish plague outbreaks during which high numbers of spores and cysts would be present in the water. Outbreaks of crayfish plague in the highly susceptible species are also a period during which spread via infected highly susceptible crayfish would be aphnomyces.
Crayfish could be harvested without the person harvesting recognizing that there was an ongoing outbreak; the crayfish may also be emergency-harvested, or be preyed upon.
Crayfish plague – Wikipedia
In the course of the disease, susceptible crayfish become progressively paralysed and show abnormal behaviour such as daytime activity normally crayfish are predominantly nocturnal. This makes them easy prey for an increased range of predators, which may eat the crayfish or abduct them to other locations.
If eaten by fish, the pathogen may survive the gut passage and be released with the fish faeces Oidtmann et al. American crayfish species carrying the pathogen as an unapparent infection can spread the disease into new areas by colonising new habitats.
Commercial trade of live crayfish for human consumption, accidental co-transport during fish transport, and use of crayfish as bait for fishing may assist colonisation of new areas. Data from North American crayfish populations tested to date suggest that the majority of populations are carriers of the pathogen Oidtmann et al.
Therefore every translocation of North American crayfish into previously A. The risk of further spread of A.
It is already fairly widespread in many parts of continental Europe due to the spread of North American crayfish species, which may carry it as a subclinical infection. A broad range of potential pathways of spread exists in areas with North American crayfish presence in the wild. The range of transmission pathways is more limited in areas where North American crayfish do not occur in the wild. The extent of spread of North American crayfish species varies between European countries; accordingly the level of risk associated with the presence of carriers of the pathogen will vary.
Potential pathways of spread were summarized in a preliminary study. Sources of spread of carrier crayfish were identified for England and Wales, where they included fish farms, natural waters, crayfish farms, garden ponds, restaurants and aquaria.
Modes of spread of A. Depending on customs in other countries these routes may vary. Routes of introduction into new geographic areas will be most likely through the import of North American crayfish for food, the aquarium trade or for aquaculture purposes.
Vegetative hyphae of A. Actively growing hyphae are densely packed with coarsely granular cytoplasm with numerous highly refractile globules Alderman and Polglase, Older hyphae are largely vacuolated with the cytoplasm mainly restricted to the periphery. Old hyphae appear devoid of contents. They develop from undifferentiated vegetative hyphae, and are delimited by a single basal septum in the case of terminal sporangia and by septa at either end of the sporangial segment in intercalary sporangia.
Although the ends of these cytoplasmic units become rounded, they remain elongate until and during discharge. Spore discharge is achlyoid, that is, the first spore stage is an aplanospore that encysts at the sporangial orifice.
Encystment of primary spores is marked by a gradual rounding up followed by the development of a cyst wall. Spores remain encysted for 8—12 hours. Release of secondary zoospores from the cysts is papillate, the papilla developing shortly before discharge. The spore cytoplasm emerges slowly in an amoeboid fashion through a narrow pore at the tip of a papilla, and there the spore shape changes gradually from spherical to reniform. Active motility takes some 5—20 minutes to develop dependent on temperature and, at first, zoospores are slow and uncoordinated.
The introduction of crayfish plague led to the disappearance of crayfish species native to Europe. Data on the economic impact of these historic introductions of crayfish plague are not available.
However, across Europe, native crayfish have been widely used as food. Crayfish have historically provided food for the poor, since catching them was not regulated in contrast to wild game. Crayfish have also been widely traded across Europe. Therefore, the livelihood of anyone involved in catching and trading of crayfish was affected.
Traditionally, five crayfish species have been considered indigenous to Europe:. Of these, it is mainly Astacus astacus and Astacus leptodactylus that have been exploited for harvest. In medieval Europe crayfish caught in rivers were a highly esteemed food resource.
The impact of crayfish plague on harvest is probably best documented through its introduction into Turkey, where harvests declined from metric tonnes in to an average of less than metric tonnes between and as a result of the disease Ackefors, Another area of economic impact to be considered is the costs of conservation of the native crayfish species that are affected by the spread of crayfish plague.
However, the costs of conservation attempts for native crayfish have never been collated to the knowledge of the author. The consequence of an introduction of Aphanomyces astaci into the natural range of the highly susceptible European species is usually the disappearance of populations of these species in affected areas.
In Europe, crayfish aphaanomyces considered a keystone species, due to the pivotal role they have in food webs and the ecology of the freshwater environment.
If they are removed for example as a result of a crayfish plague outbreakthe ecosystem is heavily affected. The proportions of most other species will be affected. An example of the relevance of crayfish as a keystone species is Sweden. The water temperatures in many lakes in Sweden are too cold to support resident fish species.
When crayfish are removed as a result of crayfish plague, macrophytes and opportunistic invertebrates often expand, causing great fluctuations of species, imbalance and reduced biodiversity. The impact of crayfish plague on a native crayfish species is fairly well documented in Sweden. Austropotamobius pallipes is considered a flagship species of patrimonial value.
Astacus astacus is highly valued — both from a recreational and economic point of view Souty-Grosset, The impact of the decline of the native crayfish as a result of spread of crayfish plague and spread of North American crayfish has been very well studied in Sweden, where crayfish fishery has a substantial social, cultural and economic value.
Traditionally, crayfish parties take place in August of each year, which almost all Swedes participate in. The decline in the supplies of native Astacus astacus as the result of the introduction of crayfish plague in led to the introduction of North American crayfish to replace the Astacus astacus populations that had been lost to the disease.