Beware the Shabby Yabby

The Yabby was introduced to farm dams in Western Australia in 1932 and has spread extensively throughout the Wheat-belt Region of the southwest of the state. Commercial harvesting of yabbies commenced in W.A. in the mid 1980's and has grown rapidly in recent years. Product harvested from farm dams is sold locally and exported to overseas markets in Europe and Asia.

A Marron with Microsporidiosis

Health tesing of yabbys has revealed very few diseases in farmed and wild yabby populations.

These include microsporidiosis which was probably introduced with illegal imports of yabbys from the eastern states; and a small undescribed virus. Testing for crayfish plague fungus (Aphanomyces astaci) since 1989 has supported the claim that this devastating and internationally reported disease is not present in Australia

Microsporidiosis is a disease caused by a spore-forming group of protozoans that infect the muscle of freshwater crayfish. The spore masses invade the muscle of the yabby to produce white streaks or nodules. In advanced cases the muscle is largely replaced by the spores and appears whitish, leading to the names "cotton-tail" or "porcelain disease". Upon cooking an infected yabby, the muscle crumbles. Microsporidiosis is not a risk to human consumers, however it is unsightly and renders the yabby inedible.

The yabby virus is detected by the presence of inclusion bodies in the cells of the deigestive gland, antennal gland and hindgut. These have been confirmed by electon microscopy as paracrystaline arrays of 13-19 nm particles and it is widespread at very low prevalence (<5%) throughout the south-west. The virus is totally harmless to humans.

No effective treatments are available for these diseases and as the life-cycle is mostly unknown, prevention by restricting importation, is of the utmost importance to stop the spread in Western Australia.

Moving freshwater crayfish into, and around the State without government authority and thorough health certification could be a very costly event for the whole industry.

The yabby industry in Western Australia is currently in a growth phase. The potential for further expansion is recognised both interstate and overseas. The industry in WA has the reputation of being relatively disease-free and it is imperative that this situation be maintained.