Yabby - preparation for market

Yabbies feed on detritus (decaying material).  Yabbies are much tastier if their gut has been emptied after harvesting and prior to sale. In order to improve the flavour, harvested yabbies need a period of cleansing in holding-tanks (purging) to empty the gut.

This information will outline the most efficient ways to maintain good water quality in holding tanks as well as other management practices that may be carried out while yabbies are in the tanks.

Water quality in holding tanks

It is important to maintain water quality in holding tanks or the health and quality of the yabbies will deteriorate. Nitrogenous waste, excreta and other waste products of yabbies can build up over several days to levels harmful to yabbies. The problem is worse when holding tanks are not cleaned between batches.

Yabbies excrete un-ionized ammonia (NH3) which is converted to nitrite (NO2) and then to nitrate (NO3) by bacteria. All three compounds (NH3, NO2 - NO3-) are toxic to yabbies; therefore, it is important to test water in holding tanks to ensure levels remain safe.

Ammonia (NH3) has a high level of toxicity, as does nitrite (NO2). Nitrate (NO3) is regarded as a low toxin.

Nitrite and un-ionized ammonia levels should be kept below 0.1ppm (parts per million) and nitrate, below 25ppm. Ammonia, nitrate and pH test kits are readily available from aquarist suppliers and if levels are found to be more than those recommended, the water should be changed. Dead yabbies will cause a rapid deterioration in water quality, therefore regular checking and removal is necessary.

Since excreta and uneaten feed cause ammonia and nitrite build-up, it is important not to over-feed in a holding tank. Siphoning or removal of the standpipe may remove the waste sediment at the base of the tank. Regular water exchange and/or biofiltration can maintain water quality and dissolved oxygen should be maintained above 3ppm.

Recirculation systems and biofiltration

Because nitrate (NO3) is much less toxic than ammonia or nitrite, it is beneficial to speed up the conversion process from ammonia to nitrite to nitrate. Bacteria in a biological filter can do this by oxidizing ammonia to nitrate.

The bacteria attach to the surface of the media of the filter; therefore, the larger the surface area of the filter, the greater the area for bacteria to colonise.

Biological filters need a continual circulation of water throughout the media and oxygen. Reference texts should be consulted to determine the amount of media and flow rate required for the particular biomass of crayfish to be supported. Biofilters require clean water free of organic matter and fine suspended solids.

Surface temnocephalid worms

The marketability of yabbies will be reduced if the shell is stained or is covered by surface parasites.

Free moving adult flatworms (Temnocephalid worms), 1 to 3mm long, can be seen on the shell and can be removed by a bath of salt.

Their unsightly eggs laid under the tail and around the gills in particular are resistant to these baths and the eggshells remain attached even after the worms have hatched.


Epistylis, a microscopic protozoan attached by stalks 5 - 10mm long and visible as an off-white to brown cotton wool-like fuzz on the shell, can be removed by a salt bath, followed by transfer to clean tanks. However, it takes several weeks for all of the stalks to disappear. Epistylis growth is a result of very poor water quality and its presence indicates that water management practices should be reviewed.

Temnocephalid worms and epistylis may be removed by the following treatment:

Salt bath - Use rock or sea salt or artificial sea salt from aquarist suppliers, but not table salt.  Dose: either 30 grams per litre of bath, for 2 to 3 minutes; or 10 grams per litre of bath, for 30 minutes. Add the required salt to the water holding the yabbies, and allow to dissolve slowly.

Shell staining

Yabbies may have a fine deposit of organic matter iron or manganese on the shell, giving them a black appearance.

All forms of surface fouling will be lost when the yabby moults. Given the time commitment for removal of surface fouling, the best strategy would be to return the yabbies to a clean pond and wait for moulting to occur.White tail disease

Yabbies infected with the microsporidian, Thelohania, have an opaque or whitish blotched abdomen. Yabbies in this state are weakened and often die in transport. The flesh is also of poor quality.

As there is no known treatment for Thelohania, it is advisable to screen out and destroy infected animals.

Transportation of live yabbies

Live yabbies can be packaged and transported in foam boxes. The yabbies are packed in successive layers with moist packaging material, such as woodwool or onion bags placed above and below each layer. A coolant such as ice or gel-refrigerant should be placed at the top and base of the box. It is essential that the crayfish are not in direct contact with the coolant. Ideally crayfish are cooled to 10° C prior to packaging.

Airlines have stringent requirements concerning transportation of live seafood aimed at eliminating leakage from seafood shipments. If considering air-transport the appropriate carrier should be contacted for advice on transportation requirements. Exports of live fish or invertebrates will require an approval permit. Check with the Australian Quarantine Inspection Service.


Part of this information is extracted from WA Fisheries Department - Fish Information 5/91 "Health and Handling of Harvested Yabbies" by J S Langdon.


Forteath, N. 1990. A Handbook of Recirculation systems for Aquatic Organisms. Fishing Industry Training Board of Tasmania.

Spotte, S. 1979. Fish and Invertebrate Culture, Water Management in Closed Systems, Wiley, Brisbane.