A health survey of farmed red-claw crayfish, Cherax quadricarinatus (von Martens), in tropical Australia

Abstract

A survey of seven Cherax quadricarinatus farms in north Queensland was conducted to ascertain the disease status of this industry. Cherax baculovitus (CBV) was found in six farms, with a prevalence of 5.9 to 59.1%. A chronic bacteraemia was common in two farms which exhibited the highest prevalence of CBV and Psorospermium sp. A microsporidian infected 4.5% of crayfish from one farm exhibiting CBV/bacteraemia.

A hepatopancreocyte nuclear lesion was caused by Cherax Giardiavirus-like virus (CGV) similar to the Giardiavirus of the Totiviridae. Cherax Giardiavirus-like virus was common to all farms surveyed with the highest prevalence being 52.3%.

Chronic, low-grade mortalities were experienced at one farm infected by the
CBVbacteraemia disease syndrome. A number of agents were associated with moribund crayfish including CBV, bacteria, CGV, Psorospermium sp., rickettsiales, and an endoparasitic ciliate. All pathogens appeared capable of killing the adult crayfish. Necrosis of eyes was common in crayfish from the same farm. Externally, the eye lesions were brown to orange, and progressed to fulminant infections totally eroding the infected eye. Psorospermium sp. and heavy bacterial loads resulted in massive granuloma formation and relocation of the black melanin of the infected eyes. Aeromonas hydrophila and Aeromonas sobria were regularly isolated from the eye lesions and the haemolymph. On some occasions faecal coliforms including Plesiomonas shigelloides, Klebsiella pneumoniae and Shewanella putrefaciens were isolated.