Rural Industries Research & Development Corporation

The New Rural Industries
A handbook for Farmers and Investors

Marron

Introduction

Marron (Cherax tenuimanus) is a large freshwater crayfish native to the main permanent rivers in the forested, high-rainfall areas in the south-west of Western Australia.

Marron is one of the largest freshwater crayfish in the world and, consequently, has been the subject of continued interest for aquaculture.

Marron farming was pioneered by Dr Noel Morrissy in the mid 1970s. His initial research achievements included elucidation of the life cycle of marron. Over the ensuing 25 years he developed a system for the semi-intensive farming of the species. Much of this information is published and is available to prospective farmers. Consequently, there is now a good understanding of the basic biology and aquaculture requirements of the species, as opposed to early attempts at farming in the 1970s, when very little was known about marron.

Marron, like other Australian freshwater crayfish, are much in demand in international markets because of their large size, high quality, acceptance by European markets as a replacement for diminishing stocks of their own native crayfish, freedom from major diseases and ability to be landed alive in the major international markets.

Marketing issues

The principal export markets for marron, as a live product, are in Asia and Europe. Marron farmers currently sell both small juveniles for stocking ponds and larger marron for local and export sales.

One of the key strengths of marron 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.

Marron are marketed either by individual farmers or by co-operatives which combine the produce from a number of small farms in order to fulfil larger orders. The latter is a recent development. Grades and the prices that farmers receive for their marron vary throughout Australia. Average grades and farm-gate values are presented in Table 1. Higher prices are paid for marron which are purged, graded and/or packed by the farmer. Markets generally pay higher prices for larger marron, which reflects the demand for larger crayfish and the increased time required to grow larger animals.

The annual production of marron has increased steadily since 1979, aside from a decrease in the late 1980s, when the main focus of farmers shifted from production of marron ready for market to supplying juveniles to stock new and expanding farms

Recently there has been a resurgence of interest in marron farming, in part because they are the highest valued freshwater crayfish farmed in Australia. This has resulted in significant investment in well designed and constructed purpose-built farms, and increased production from farms in Western Australia and South Australia.

Production requirements

Marron are currently farmed in Western Australia, South Australia and NSW . They are not permitted in Victoria. The area of Australia potentially suitable for marron farming, shown on the accompanying map, is determined by temperature, water supply and the occurrence of clay soils suitable for ponds.

Marron do not grow at temperatures below 12.5°C. The temperature for maximum growth is 24° C. Above this temperature, marron growth declines rapidly, and the animals cannot survive temperatures of 30°C for long periods. mortalities occur at 30^°C and above, depending on exposure time.

Marron occur in waters which generally have pH levels ranging between 7.0 and 8.5.

Dissolved oxygen levels should be maintained at or above 6 parts per million (ppm) and marron become stressed when levels drop below 3 ppm. As marron are susceptible to low levels of dissolved oxygen, the use of aeration is recommended in ponds to maintain dissolved oxygen at adequate levels and to avoid stratification, stagnant bottom water and anoxic sediments.

Although marron can tolerate salinities ranging from freshwater to 15 parts per thousand (ppt), low salinities are most suitable for farming, as growth decreases when salinity is above 6-8 ppt.

Varieties

Marron are native to the south-west corner of Western Australia, and a number of licensed hatcheries operate in that State. These sell juvenile crayfish under 1 year old (0+) for stocking farms in Western Australia and elsewhere.

Most established farmers produce their own juveniles for stocking their ponds. Marron mate in early spring and, depending on the size the females, incubate 450-900 eggs, until releasing juveniles in early summer. Hatchery performance is measured as the number of surviving 0+ juveniles reared per female—200 is considered excellent.

Broodstock marron are at least 2, and usually 3 years old. During the non-breeding season, they should be held in small earthen broodstock ponds at a density of four individuals per m², a ratio of one male to every three females and be well fed.

As the breeding season approaches, broodstock should be transferred into 100-150 m² spawning-nursery ponds for mating. Approximately 75% of 2+⁺-year-old females become berried, after which the males and non-berried females should be separated from the berried females. A supply of artificial weed, which can be examined periodically, makes it easier to monitor released juveniles, and provides shelter for them. To prevent cannibalism, the adult females should be removed immediately after the juveniles (0+-year-olds) are released.

At least three varieties of marron exist within the range of this freshwater crayfish. The potential of these varieties, and of others that may also be present, has not yet been scientifically evaluated.

Fish husbandry

In Western Australia, attempts have been made to culture marron in farm dams, ponds, tanks and battery cultures. The success of battery and tank cultures has been limited by the unavailability of a suitable diet and poor growth at high density.

Although both farm dam and pond cultures have been exploited in Western Australia, the efficiency of these two methods varies considerably. Unfed farm dams usually produce only 100-300 kg/ha/year, while purpose-built semi-intensive ponds, incorporating a daily feeding regime, have been producing 1000-4000 kg/ha/year, depending on stocking rate. In addition, semi-intensive pond production permits draining and grading of stock. This enables the management of a marron crop to maximise both biological and economic productivity.

The relative merits of semi-intensive pond culture and farm dam culture of marron are described by Morrissy (1992).

Semi-intensive grow-out ponds are usually rectangular and 1000 m² in surface area. Although larger ponds may be built, they are more difficult to manage. Ponds should have a maximum width of 20-25 m and be situated with their long axis parallel to the prevailing wind direction to increase aeration.

Marron ponds should be located side-by-side with an access road between each pond. Ponds should have paddlewheel aerators and be constantly topped up to replace water lost through evaporation and seepage.

The pond floor should slope from a minimum depth of 1.0 m to a maximum of 2.0 m, with a gravity-feed drain pipe in the deep end. The pond floor should be well compacted and consolidated with road limestone or gravel, upon which should be placed between 100 and 200 artificial weed bunches per 1000 m² to provide shelter. The bottom gravity-feed drain should have a 3 m² concrete collection basin around the base to facilitate harvesting.

Semi-intensive grow-out ponds require overhead bird mesh and artificial shelters to prevent predation. Ponds also require perimeter fencing to prevent marron from crawling out and water rats or other predators from entering.

The 0+ juvenile marron should be held in smaller spawning-nursery ponds (see above) for around 6 months. The grow-out ponds should be stocked with 0+-year-old juvenile marron in mid winter at a density of 3-5 per m².

Marron are omnivorous, feeding on detrital material such as rotting organic matter at the bottoms of rivers or ponds.

Commercial operators use a combination of a pelleted marron diet and natural foods in outdoor earth ponds. Pelleted diets added to marron ponds feed the marron directly, but also contribute to establishing a natural food chain in the pond. Although marron have been reported to grow to 2 kg, it is more economic to harvest farmed marron at much smaller sizes.

Depending upon culture conditions such as water temperature, nutrition and stocking density, marron can grow to 60-100 g within 12 months and to 100-300 g within 24 months.

Marron have a commercial `tail with shell' recovery rate of 43%. This is higher than the commercial tail recovery rate for other cultured freshwater crayfish and compares favourably with the 40% obtained from marine rock lobsters.

For further information on culturing marron, the reader should consult `An introduction to marron and other freshwater crayfish farming' by Dr Noel Morrissy (1992), published by the Fisheries Department of Western Australia.

Pest and disease control

The shells and gills of marron, in common with those of all freshwater crayfish, may be home to a number of very small, attached animals called epibionts. They include the stalked, ciliate protozoan Epistylis and a small flatworm Temnocephala, and they cause problems only if they occur in large numbers and affect the marketing appearance of the marron. Although epibionts do not directly harm the crayfish, their occurrence is symptomatic of poor water quality and slow growth.

Only two diseases have been reported in marron: microsporidiosis caused by a pleistophorid; and Thelohania.

Thelohania is a protozoan which causes `Cotton tail' or `porcelain disease'. It has been reported in crayfish in the eastern States and in gilgies in Western Australia, but has not been found in marron in WA. Consequently, the translocation of crayfish should be strictly controlled to ensure that Thelohania is not introduced into disease-free stocks from Western Australia.

The importation of all overseas crayfish species into Western Australia is prohibited, since they carry the crayfish plague fungus Aphanomyces astaci, to which all Australian crayfish are very susceptible.

Harvesting and postharvest handling

Unlike some other freshwater crustaceans, marron do not burrow to escape drought. This facilitates harvesting and ensures that the integrity of pond walls is not compromised.

Marron are usually harvested by draining ponds and collecting animals by hand. It is preferable to harvest during the coolest part of the day. After harvest marron need to be gill washed immediately, then held in a cool, moist atmosphere. This prevents mortalities from infections by bacteria in bottom sediments trapped in the gill chamber.

As marron are exported alive, very little processing is required. Before packing for export the processor places freshly harvested marron into purging tanks. The marron remain in these tanks, where they are not fed, for a minimum of 48 hours to purge their hind guts and improve the flavour.

The marron are graded according to condition and the weight grades presented previously (1).

Marron can live for many days out of water, and can be shipped alive if held in cool, moist air. If immersed in water without aeration they will drown. To ensure that the marron 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

In general the establishment costs for a semi-intensive marron farm average $50-$60,000 per hectare of water area of ponds constructed. This includes the cost of pond construction, consolidation, bird netting, electricity, aeration and drains. When managed correctly these semi-intensive ponds will optimally yield 2500 kg of larger marron per hectare of water area per year, but up to 4000 kg of smaller marron can be produced per hectare.

Because of the commercial confidences of existing marron farms, accurate information on income and operating costs is hard to obtain. Recent economic evaluations have shown that a properly constructed and managed, marron farm will return a gross income of $40,000 per hectare of ponds per year, with operating costs around $15,000 per hectare per year. This provides the farmer with a net income of around $25,000 per hectare of ponds per year.

Consequently a marron farmer can expect to receive a return on investment of around 30%, which compares favourably with other forms of primary production. Like all forms of farming returns may vary with farming methods and site characteristics.

Key statistics

Key contacts

Key references

Lawrence, C.S., Morrissy, N.M., Penn, J. and Jacoby, K. (1995) Marron (Cherax tenuimanus). Aquaculture WA, No. 2. 4,p.

Morrissy, N.M. (1976) Aquaculture of marron, Cherax tenuimanus (Smith) Part 1: Site selection and the potential of marron for aquaculture. Fisheries Research Bulletin, No. 17.

Morrissy, N.M. (1976b) Aquaculture of marron, Cherax tenuimanus (Smith) Part 2: Breeding and early rearing. Fisheries Research Bulletin, No. 17.

Morrissy, N.M. (1990) Optimum and favourable temperatures for growth of Cherax tenuimanus (Smith) (Decapoda: Parastacidae). Australian Journal of Marine and Freshwater Research, Vol. 41 (6), 735-46.

Morrissy, N.M. (1992) `An introduction to marron and other freshwater crayfish farming in Western Australia.} Fisheries Department of Western Australia. 36 p

Morrissy, N.M., Walker, P. and Moore, W. (1995) Predictive equations for managing semi-intensive growout of a freshwater crayfish, Cherax tenuimanus, on a commercial farm. Aquaculture Research, Vol. 26, 71-80.

*About the author