Effect of husbandry on the emergence of pathogens in the aquaculture of redclaw crayfish (Cherax quadricarinatus) in Australia

The redclaw crayfish ( Cherax quadricarinatus ) industry has existed for four decades but has failed to thrive. Part of this is due to continued setbacks due to disease. Some of these diseases have been ameliorated by changing husbandry. Herein, we outline the temporal discovery of pathogens and what measures changed the disease landscape. The first change to disease prevalence was when the industry changed to pond-reared broodstock from wild-caught broodstock. Pathogens like microsporidians ( Astathelohania ) and rickettsia ( Paracoxiella cheracis ) seem to need intermediate or alternate hosts and their prevalence plummeted. The next major change was the advent of hatchery produced juveniles that incorporated surface-sterilization of eggs. The prevalence of heirloom viruses (nudivirus, giardiavirus and reovirus) in particular, almost disappeared. Stress events of all kinds often precipitated epizootics. The combination of hatcheries, stress and surface sterilization brought the importance of bacterial disease ( Aeromonas ) to the fore which was solved for many years by bacteriophage intervention. The impact of transport stress allowed cryptic viruses (iflavirus and bunyavirus) to negatively influence production and be discovered. Often, crossing family lines to increase genetic diversity without due attention to the pathogens they carried allowed viruses and sometimes rickettsia to become widespread in the industry. A population of crayfish resistant to iflavirus has been discovered and awaits commercial exploitation. Lastly, the resilience and determination of the crayfish farmers in spite of these challenges must be acknowledged. • The redclaw crayfish industry has been operational for four decades. • Husbandry changes have led to both the emergence and reduction of pathogens. • Removing wild caught broodstock eliminated Astathelohania and reduced Paracoxiella. • Using hatchery raised craylings for stocking greatly diminished the heirloom viruses. • New cryptic viruses have been discovered with SPF crayfish for one identified.