Rural Industries Research & Development Corporation

The New Rural Industries
A handbook for Farmers and Investors

Yabbies

Introduction

Yabbies (Cherax albidus and Cherax destructor) are indigenous to central and eastern Australia and have received considerable aquacultural interest. Although some yabbies are produced from ponds on purpose-built farms, the vast majority of commercial yabbie production in Australia comes from trapping in farmers' dams what are essentially wild yabbies. This use of existing farm dams originally built to water stock has enabled rapid expansion of the industry because of the low entry cost. The yabbie industry currently harvests around 4000 farm dams in Western Australia. The rapid growth experienced by the industry is expected to continue, with processors reporting an increase this year of up to 400% in the number of farmers harvesting yabbies.

Australian yabbies are in demand internationally due to their high quality, larger size than crayfish produced by overseas competitors, acceptance by European markets as a replacement for diminishing stocks of their own native crayfish, freedom from major diseases and ability to be landed live in the major international markets.

Markets and marketing issues

Yabbies are sold both domestically and in export markets in Europe and Asia. Approximately 70% of Western Australian yabbie production is exported.

One of the key strengths of yabbies is that they can be exported alive, out of water and arrive in prime condition not only in capital cities in Australia, but also on high value markets in Europe and Asia. International demand for freshwater crayfish is expected to continue to increase. This is the result of a number of factors, but particularly continuing demand from traditional European consumers of freshwater crayfish combined with decreased domestic supplies there because of crayfish plague, a disease which has swept through Europe killing many of their native populations of freshwater crayfish. Australia is the only continent with freshwater crayfish that have not been infected by the disease, and our strict quarantine regulations should ensure that this valued status is maintained.

Yabbies are graded according to weight and condition. Weight grades and prices vary around Australia. Average weight grades are presented in Table 1. Higher prices are paid for yabbies which are purged, graded and/or packed by the farmer. Most processors pay higher prices for larger yabbies; this reflects the demand for larger crayfish and the greater difficulty in producing large yabbies. As the price of wild caught yabbies may drop as low as $2.00/kg, it is essential that all farmed yabbies are clean, purged and graded in order to maintain their market share and higher prices.

Production requirements

The production of yabbies from farm dams has experienced rapid growth over the past 10 years, from a total of 1.5 t in 1987 to almost 300 t in 1994 (Fig. 1). Nevertheless, the production of yabbies from farm dams can be affected by drought, as was the experience in 1995-96 when low rainfall resulted in many farm dams drying up with a consequent reduction in yabbie harvests.

The production of yabbies from `semi-intensive' ponds has shown slower, but steady, growth over the past 10 years, with production increasing to around 50 t in 1995-96.

The regions in which yabbies are currently farmed are shown on the accompanying map, but the distribution of yabbies is much wider than the farming areas—they occur naturally throughout most of central and eastern Australia.

In farm dams and ponds, yabbies spawn annually from early spring to mid summer. Yabbies spawn so readily there is generally no need to purchase juveniles, with most farms producing more stock than they require. In fact, a major problem in yabbie farming is the over-population of yabbie dams and ponds, which results in stunted growth and smaller individual animals.

Yabbies thrive in the warmer, drier, inland regions of Australia. Optimal water temperatures for growth are in the range 24-28°C. Growth ceases at water temperatures over 34°C and below 15°C during winter.

Growth of yabbies ceases at salinities above 8 parts per thousand (ppt), which is about one quarter seawater. At salinity levels above about half seawater mortalities occur.

Yabbies can tolerate dissolved oxygen levels lower than one part per million (ppm) for short periods. However, feeding activity, and hence good growth, are dependent upon healthy, well-oxygenated water conditions.

For many farmers, the major limitation to increased yabbie production is the amount of water available. Sites for yabbie farming must have soils containing sufficient clay to minimise seepage and adequate rainfall or water supplies to not only fill dams or ponds but also replace water lost due to evaporation and seepage.

Varieties

The name yabbie is derived from an Aboriginal word for freshwater crayfish. Although the taxonomy of yabbies has been reviewed a number of times, in general, these studies have focused upon whether different varieties of yabbies belong to the same or separate species. From an aquaculture perspective, it is perhaps more important to recognise that there are a number of `varieties' of yabbies, some of which are more suitable for farming than others.

Cherax albidus is the species to which the yabbies found in Western Australia belong. These yabbies, originally from Merwyn Swamp in Victoria, were introduced into farm dams around Narembeen in Western Australia around 1932. Most of the yabbies found in central and eastern Australia are Cherax destructor, a closely related species.

Although there are a number of `varieties' of freshwater crayfish which are collectively referred to as yabbies (i.e. Cherax albidus, C. destructor, C. cuspidatus, C. rotundus) most yabbies produced in Western Australia are Cherax albidus and in central and Eastern Australia either Cherax albidus or Cherax destructo.

Seed stock is available throughout the range in which yabbies occur naturally. As yabbies reproduce readily in farm dams or ponds only an initial stocking is usually required, after which supplies of juveniles can be produced easily in the pond or dam.

Fish husbandry

Farmers producing yabbies using extensive farm dam production have reported yields of
400-690 kg/ha of water area per year. However, as a result of uncontrolled breeding, a significant portion of this production is below market size. Farm dams cannot be readily drained for (i) efficient harvesting during winter; (ii) stock control against over-breeding; or (iii) cleaning out of the bottom mud when sediments become over-enriched. Juveniles may be stocked in farm dams at 1-2 individuals per square metre.

Harvesting yabbies from dams by seine netting damages the animals and can result in bacterial infection from mud stirred up from the bottom. Consequently, yabbies are harvested from dams using baited traps.

Because yabbies are less inclined to feed in winter, capture becomes more difficult using baited traps at low water temperatures. Consequently, the harvesting of yabbies from dams by trapping results in seasonal fluctuations in supply similar to that experienced in wild fisheries.

The use of purpose-built ponds for more intensive crayfish farming has a number of advantages over widely spread and isolated farm dams. Semi-intensive crayfish production in such ponds gives average yields about 5 times those of farm dams. These ponds may be rapidly and completely drained via a gravity drain outlet for complete harvesting, pond repair, bottom cleaning, liming and disease control by allowing the ponds to dry out. Ponds used in yabbie farming are usually 0.5 - 2 m deep at the outlet and about 0.1 ha in water area. Each pond has a piped water supply and a water level standpipe in the pond's bottom outlet. The pond outlet has a screened concrete sump to collect yabbies.

A set of ponds is fenced and may also have bird netting to exclude predators. To prevent temperature and oxygen stratification, good ponds have a very small freeboard, less than 0.5 m, between the top bank and the water level. Also, the long axis of the pond should be aligned with the prevailing wind to enhance circulation and oxygenation. The high rate of daily feeding needed to get the high production levels in semi-intensive yabbie culture, requires the installation of a mechanical, mains-powered aerator. Juveniles may be stocked in these semi-intensive ponds at a density of 5 individuals per square metre.

Due to the leaching of nutrients, the development of nutritionally complete diets for freshwater crayfish is complex. Consequently, while supplementary feeding is essential for higher than natural crayfish production, crayfish make up for the deficiencies of essential micronutrients in the artificial feed by also eating natural food in the dam or pond. Nutrients which leach from the artificial feed, fertilise the water body and encourage the production of natural foods.

Currently, the most common feed used for yabbies in farm dams in WA is lupins, at the rate of 2.5 g/m² of water area each week. However, improved growth rates for yabbies in farm dams have been achieved using crayfish pellets at the rate of 2.5-5 g/m²/ week. In semi-intensive pond production, yabbies are usually fed crayfish pellets at between 2.5-10 g/m² each week. Use of aerators allows the higher feeding rates used in ponds.

Growth of yabbies is temperature and density dependent. Although individual growth of yabbies, as in other crayfish, is always highly variable, the minimum market size of 30 g can be achieved in less than 6 months.

Key statistics

Pest and disease control

Surface fouling on yabbies by ectocommensals, such as the protozoan Epistylis and the platyhelminth (or flatworm) Temnocephala, although rarely harmful to the animals unless in extremely high densities, lowers the market appearance of affected individuals. These so-called epibionts are symptomatic of waters which are over-enriched with nutrients. This usually occurs due to nutrient enriched run-off entering farm dams or overfeeding in semi-intensive ponds.

The microsporidian Thelohania infects yabbie and other crayfish populations in eastern Australia but is not present in the West; consequently, to protect Western Australian stocks this State bans the importation of live crayfish.

All Australian crayfish, including yabbies, are susceptible to the crayfish plague of the northern hemisphere, a fungal disease Aphanomyces astaci, found on American crayfish and which has devastated European crayfish populations. Consequently, in order to protect our native populations and aquaculture industry, the importation to Australia of any species of live crayfish which may carry this disease is not permitted

Harvesting and postharvest handling

Yabbies are harvested from dams using baited traps or collected from ponds after draining.

Upon harvesting from farm dams, yabbies must be gill washed immediately to prevent mortality due to bacterial infections arising from bottom sediments trapped in the gill chamber. They should then be held in a cool, moist atmosphere.

Because yabbies are exported live, very little processing is required by commercial yabbie farms to supply markets direct. In Western Australia and South Australia a highly successful system has developed where farmers or professional yabbie harvesters trap yabbies from farm dams. The yabbies are then gill washed and placed in cool boxes which are delivered to a centrally located processor. The processor buys the freshly harvested yabbies from the farmer or harvester and places them into purging tanks. The yabbies remain in these tanks, where they are not fed, for a minimum of 48 hours to purge their hind guts and greatly improve the flavour and travelling condition.

The yabbies are graded according to condition and the weight grades shown in Table 1. The processor combines all of these small harvests from a large number of dams or ponds to provide enough yabbies to supply large international orders. To ensure that yabbies arrive at their destination in top condition, before export they are cooled, then packed between layers of foam in polystyrene boxes with ice bottles.

Economics of production and processing

The establishment costs for farm dam production of yabbies are very low. The only essential equipment is traps to catch the yabbies and containers for gill flushing and transportation. Alternatively, farmers may elect to have commercial harvesters trap their yabbies and receive a percentage of the crop value.

Commercial semi-intensive pond production is much more expensive with establishment and operating costs similar to those of a marron farm (see chapter on marron).

A case study of the economics of harvesting yabbies from a farmer's dams was undertaken in 1996 by an extension officer employed by the Fisheries Department of WA. In 1996, this farmer produced 3000 kg of marketable yabbies, which grossed $19,000. The study showed that the farmer, who had 46 dams, incurred the following costs;

Thus, after subtracting working costs from the $19,000 gross income for 1996 the farmer received $13,504 for the year.

The farmer spent 360 hours, or approximately 7 hours per week on harvesting and feeding the yabbie dams, providing a return of $37.51/hour for labour.

Key contacts

Key references

Freshwater Farmer Magazine - published quarterly

Les Gray
P.O. Box 712, MSC
Torrens Park, SA 5062

Huner, J.V. (1994) `Freshwater Crayfish Aquaculture in North America, Europe, and Australia : Families Astacidae, Cambaridae, and Parastacidae'. The Haworth Press Inc., New York. 312 p.

Lake, P.S. and Sokol, A. (1986) Ecology of the yabby Cherax destructor. Australian Water Resources Council Technical Paper, No. 87, 186 p

Lawrence, C.S., Morrissy, N.M., Penn, J. and Jacoby, K.(1995) Yabbies (Cherax albidus). Aquaculture WA, No. 4. 4 p.

Lawrence, C.S. and Morrissy, N.M. (1997) Enhancement of yabby production from WA farm dams. Freshwater Farmer, Vol. 4, No. 3, 6-7.

Morrissy, N.M. (1995) Yabbie Questions and Answers. Aquainfo Number 1, Fisheries Department of WA.

Morrissy, N.M. (1992) `An introduction to marron and other freshwater crayfish farming'. Fisheries Department of WA. 36 p.

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