ABSTRACT
Crayfi sh are hosts to a wide range of diff erent commensals, parasites and pathogens including viruses, bacteria, fungi, protistans, trematodes, cestodes, acanthocephalans, nematodes, branchiobdellids, temnocephalids and arthropods. The anthropogenic movement of crayfi sh either for aquaculture purposes or the aquarium trade has resulted in the translocation of a number of disease conditions of concern, some of which have led to great reductions in native crayfi sh populations. One of the most studied disease conditions of crayfi sh is the so-called crayfi sh plaque, caused by Aphanomyces astaci. Whilst this fungallike organism has no doubt caused complete or near extinction of some native crayfi sh populations, its infamous reputation has meant that some unexplained mortalities might have been incorrectly attributed to this disease despite clear diagnostic evidence. This view was ably summarised by Edgerton et al. (2004) who stated that such an “extreme emphasis on A. astaci has created inertia in European astacology, which has curtailed researchers, state fi sh-disease diagnosticians, and resource managers from fully assessing and considering the existence of other serious pathogens of freshwater crayfi sh and the ensuing consequences. As a result, basic skills in crayfi sh pathology have been lost or underdeveloped. Moreover, some management schemes aimed at conserving native European freshwater crayfi sh are less likely to be eff ective, and might actually be harmful, in achieving their goal because of a lack of appreciation of the presence or signifi cance of certain pathogens”. Another issue is that few studies of crayfi sh diseases consider the pathology associated with the infection meaning that assessment of the individual impact is often lacking; the bulk of studies on crayfi sh diseases appear to have been focused on descriptive and lifecycle studies. Whilst advances in diagnostic methods in recent years have ensured that, in part, correct diagnosis of an aetiological agent has been possible, this has been negatively balanced with a lack of crayfi sh pathology specialists worldwide. Of those individuals actively involved in this work, most are based in Australia, Europe and the USA. This geographical bias has meant that not all species of crayfi sh have been examined for pathogens and lead to the exciting possibilities in the future of new and novel disease conditions being described in crayfi sh across their distribution.
