Freshwater crayfish - aquaculture prospects

Introduction

Australia has one of the richest collections of freshwater crayfish in the world. All of our species belong to the family Parastacidae, which is found in Australia, New Guinea, New Zealand, Madagascar and South America.

Our freshwater crayfish range from the largest to some of the smallest in existence. The giant Tasmanian crayfish (Astacopis gouldii) grown to 6.3 kg and the Murray River crayfish (Euastacus armatus) grows to 2.7 kg. These species and spiny crayfishes in general, are considered to have little aquaculture potential because of their slow growth and low meat yield.

Three species of the genus Cherax are considered to have aquaculture potential. These are the yabby (Cherax destructor), which is found throughout much of New South Wales, Victoria, South Australia and Queensland; the marron (C. tenuimanus), which is native to south west Western Australia; and the redclaw (C. quadricarinatus), which is native to northern Queensland and the Northern Territory.

This information compares the potential of the two Cherax species for semi-intensive aquaculture within New South Wales yabby and redclaw.

The industry status

The freshwater crayfish industry in Australia is now well developed. For production figures see the NSW DPI aquaculture production report.

The only other established freshwater crayfish industry in the world is based on the red swamp crayfish (Procambarus clarkii, family Cambaridae), which is cultured in the southern United States, Spain and several other countries.

Reproduction

Both species of Cherax breed naturally in ponds. Berried crayfish (those with eggs) are kept in a separate pond or tank and the adults removed (trapped) once they have bred. When the juveniles have reached 1-2g the pond is harvested and the juveniles stocked into grow-out ponds. Many farms however do not regulate breeding size animals and crayfish will breed readily in culture ponds, leading to large size variation in stock.

Redclaw and yabbies are able to breed in their first year. All three species produce similar numbers of eggs; as the crayfish grow they become capable of producing more, to a maximum of about 1000. Yabbies and redclaws may breed several times in any one season.

Redclaw are thought to require a period of cooler water temperatures (16-22° C) followed by a temperature increase to stimulate spawning. Over the following 4-6 weeks the female nurtures the eggs, which hatch 6-10 weeks after spawning. The newly hatched juveniles remain close to the female for several weeks before becoming independent.

Yabbies breed when water temperatures exceed 15° C. Incubation of the eggs, at normal summer temperatures of 23-24° C, takes about 3 weeks. As in the redclaw, the juveniles remain with the female for a further 2-3 weeks and are then recruited into the general population.

Growth and production

Yabbies grow only when temperatures exceed 15° C. Consequently, at Narranderra (in the Riverina of New South Wales) yabbies will grow for only 6 months of the year, but at Grafton (in northeastern New South Wales) yabbies will grow for 11 months of the year. Yabbies grow fastest at 22-28° C.

At juvenile (1-2g) stocking rates of 5-10/m2 (in a grow-out pond), yabbies show 50-70% survival. Yabbies can average 40-60g in 6 months in summer conditions (above 20° C); growth rates can vary and individuals will range from 5-100g after 1 year. Redclaw show rapid and relatively uniform growth in the wild, reaching 150-300g in 2 years; under semi-intensive culture they reach 50-60g in 9 months, and growth is more variable.

Yabbies are  the most suitable for farming in NSW. Well-managed ponds may yield up to 1 tonne/ha/yr. However most semi-intensive pond-based farms in NSW achieve rates of approximately 500 kg/ha/yr.

Feeding

Adult crayfish are opportunistic feeders but are primarily detritovores (that is, they feed mainly on broken down organic matter). Their main sources of nutrition are the microbes (including bacteria and fungi) that break down leaf matter. It has been found that microbes colonise food more quickly on earth-lined ponds, which are better than concrete tanks.

Although crayfish will survive and grow without supplementary feeding, best growth rates are achieved with an augmented food supply. The amount of supplementary feed required is dependent on water temperature, stock density and the type of food given. Studies suggest that a wide range of pellets (including cheap commercially available pellets such as Lucerne or pig starter rations) can be used successfully; however, the more expensive formulated diets will generally provide slightly better growth rates. Alternatives such as the planting of forage crops may be cheaper and worth experimentation.

Juvenile crayfish are carnivores and catch small organisms in the water (zooplankton) as their main food source. If good growth rates are to be achieved nursery ponds need to have good zooplankton blooms.

Behaviour

Yabbies can be aggressive and cannibalistic under certain conditions. High survival and good growth can still be achieved when some form of shelter (for example, onion bags for juveniles) is available in the ponds.

Although  redclaw are less aggressive, shelter is still required to achieve uniform growth rates, as large crayfish dominate small crayfish. Regularly trapping the larger crayfish from the pond also helps to ensure more uniform growth rates.

Unlike redclaw, yabbies are known to burrow into dam walls. Research suggests that burrowing is a survival response to a declining water level.

Pond design and management

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.

Further Information 

For further information, call NSW DPI Port Stephens Fisheries Centre on 02 4982 1232.

References

Anon (1991). Yabby Farming Open Day Notes. South Australian Department of Fisheries and NSW Fisheries.

Gillespie, J. (1990). Redclaw: A Hot New Prospect. Aust. Fisheries, November, 2-45*

Jones, C.M. (1990). The Biology and Aquaculture Potential of the Tropical Freshwater Crayfish. Cherax quadricarinatus. Queensland Department of Primary Industries Information Series Q190028.

Mills, B.J. (1989). Australian Freshwater Crayfish. Handbook of Aquaculture. Freshwater - Crayfish Aquaculture, Research and Management, RSD. 778 Lymington, Tasmania 7109.

Morrissy, N.M. (1981). Marron and Marron Farming. Department of Fisheries and Wildlife. Western Australia.

Rowland, S.J. (1991). Site Selection and Design of Aquaculture Facilities. Fishnote DF/5, NSW Agriculture & Fisheries.

Shelly, C.C. & Pearce, M.C. (1990) Farming the Redclaw Freshwater Crayfish. Northern Territory Department of Primary Industry and Fisheries Fishery Report No. 21*.

Staniford, A.J. (1989). The Effect of Yield and Price Variability on the Economic Feasibility of Freshwater Crayfish (Cherax destructor) Clark (Decapoda: Parastacidae) Production in Australia. Aquaculture 81 (3-4): 225-235*.

Staniford, A.J & Kuznecovs, J. (1988). Aquaculture of the Yabbie Cherax destructor Clark (Decapoda: Parastacidae): An Economic Evaluation. Aquaculture Fish Management. 19: 325-340*.

* Denotes articles on the economics of farming crayfish