Chapter 38 - Crayfish plague

Abstract

Aphanomyces astaci was introduced into Europe via the American crayfish Pacifastacus leniusculus since the mid-1800s, causing severe mortalities and declines of the local crayfish populations. Crayfish plague is still a threat to the European crayfish Astacus astacus. The disease manifests as the appearance of crayfish during daylight (normally nocturnal animals) which are uncoordinated in movement. They fall onto their backs and cannot return to an upright posture. These are the first signs which may lead to mass mortalities of crayfish in a river or lake. The life-cycle consists of vegetative hyphae invading and spreading through host tissues to produce sporangia that release ameboid primary spores. The encystment of primary spores then leads to biflagellated zoospore or secondary spore formation. The infective zoospores travel in water to the next host and are chemotactically attracted to the cuticle of crayfish where there has been a wound. In this chapter, key pathology and disease information are discussed to enable proper diagnosis of the condition and differentiation from other crustacean fungal diseases.