Disease risks associated with the importation and release of non-native crayfish species into mainland Britain

Abstract

A full histological survey of 782 non-indigenous crayfish established in riverine habi- tats or imported into mainland Britain through the aquarium trade was conducted. The selected populations were subjected to further bacteriological, molecular and ultrastructural studies to characterise disease conditions. Pacifastacus leniusculus, Orconectes virilis and Astacus lepto- dactylus were obtained from 16 rivers in mainland Britain. Additionally, Cambarellus patzcuaren- sis, Cherax quadricarinatus, Procambarus clarkii and P. fallax were obtained from 8 pet shops, whilst C. patzcuarensis, Cherax peknyi, C. quadricarinatus and P. clarkii were seized at a point of entry into Britain. Tests for infections were negative in the majority of P. leniusculus (66.4%); the rest were infected with at least one pathogen or commensal, including an intranuclear bacilliform virus and a novel Spiroplasma sp. of male Sertoli cells. Low level bacterial and ciliate infections and commensal mites and ostracods also occurred on or in established signal crayfish. The estab- lished population of O. virilis was found to be negative for any visible infections; one shipment of P. clarkii and one aquarium-held population of C. quadricarinatus were also found to contain no visible infections. One shipment of P. clarkii from Singapore was infected with white spot syn- drome virus (WSSV). The bacterial species isolated from crayfish included Aero monas hydrophila, A. sobria, Citrobacter freundii, Grimontia hollisae, Hafnia alvei, Pasteurella multocida and Week- sella virosa. The results are discussed in relation to the enemy release hypothesis, and the risk associated with the transboundary trade in non-indigenous crayfish is considered as a potential source of disease to native crayfish species.