If the farm is to be built on a new property it is important to determine the water holding ability of the soil. Ideally, ponds should be built on a clay base covered with 10-30cm of topsoil. The topsoil will provide a nutrient-rich substrate and will increase productivity in the pond.
Consideration should also be given to the running costs of ponds. Ponds should be drained, have water supply and aeration. It is recommended that ponds be periodically drained to allow aerobic breakdown of any remaining organic matter and removal of sediment.
Water temperature:
- Yabbies and redclaw both show maximum growth at about 28° C and have an upper lethal temperature (ULT) of 36° C.
- Redclaw start to perish at 34° C.
- Whereas yabbies are very tolerant of cold, redclaw juveniles repeatedly experience heavy mortality below 8° C, and growth is generally poorer in NSW than the warmer waters of Qld and Northern Australia.
Water quality:
Both species tolerate salinity to a level half that of seawater; however salinity levels in ponds should not regularly exceed 2ppt or growth and behaviour may be affected. Yabbies and redclaw will tolerate very low oxygen levels. Good growth rates will only be achieved if conditions in the ponds are ideal (dissolved oxygen levels above 6ppm), and warm water temperatures (25°C).
The critical pH range is 7-8.5. Levels much below 7 cause moulting and shell hardening problems in yabbies. Low calcium levels (hardness less than 80ppm) has the same effect.
Diseases and parasites:
Australian freshwater crayfish appear to have only one major disease, the so-called porcelain or white tail disease caused by a microsporidian. The disease appears to be transmitted through cannibalism of dead individuals. The disease cannot be treated but can be managed in aquaculture if
stock is periodically examined, and diseased animals removed. Microsporidians have been found in both Cherax species. A temnocephalan (a small ectocommensal flatworm) is often found in large numbers on the gills or shells of freshwater crayfish. It rarely presents a management problem and can be controlled with salt baths under tank conditions.
Many European countries have had their crayfish stocks destroyed by the so-called “crayfish plague”, caused by fungus Aphanomyces astaci. It originated in the United States and spread to Europe with introduced crayfish.
This fungus is not present in Australia, but tests have shown that if it were to reach Australia it would destroy many of our crayfish stocks. To stop this fungus destroying our unique crayfish fauna, the import of crayfish into Australia has been prohibited.
Marketability:
Both species have small claws. Redclaw have a meat yield (meat to body weight ratio) of 22-25%; the meat yield is slightly lower in the yabby. The size of the domestic market is unknown. Yabbies have been marketed in small quantities from the wild fishery for years.
Much higher prices (above $20/kg) have been obtained for both species by supplying live crayfish of a particular size to restaurants.
Farmers currently receive prices a range of live crayfish, depending on size, buyer and season. For average price figures see the NSW DPI aquaculture production report. Live crayfish are also regularly available from large retail outlets including the Sydney Fish Market. The size of any export market is impossible to evaluate until supply can be maintained.
There is certainly a market for crayfish in Europe, as crayfish are regarded as a delicacy and local stocks have been diminished by the “crayfish plague”. However, the market in some European countries (for example, Sweden) is highly seasonal.
Trial shipments have suggested that Cherax species would be accepted in the marketplace. Some products have also been exported and well received in Asia, so there is also potential there.
The success of future export trade will be largely dependent on volume and continuity of supply.
Conclusion:
Crayfish is a steady aquaculture industry in NSW, however there is much potential for further development. The yabby is the most suitable species for NSW due to its natural occurrence and tolerance to the wide range of conditions and climate. Further research is required to determine production methods for yabbies under semi-intensive purpose built, pond conditions.
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