Production requirements

Redclaw is a tropical species endemic to north-west Queensland and the north-east of the Northern Territory. The harsh physical extremes of this distribution have given redclaw a robust nature with broad climatic tolerances.
Its preferred temperature range (water temperature) for >70 percent of maximum growth rate is 23ºC to 31ºC. Temperature extremes beyond which redclaw will perish are 10ºC and 36ºC.
Reproduction will only occur while water temperature remains above 23ºC. While suitable temperatures prevail throughout Queensland during summer, the shorter and less extreme winter period in more northern areas confers a significant advantage.
Most industry growth is expected to occur north of Bundaberg, including parts of western Queensland, northern Northern Territory and the Kununarra region of Western Australia.
This map broadly indicates the regions suitable for redclaw production.
Redclaw aquaculture necessitates earthen ponds which hold water. Consequently, soil must have a reasonable clay content and be free of rock. Ponds are typically 1,000 sq.m in surface area, with a depth of between 1.0 and 2.5 m. Their specification and design can have an important bearing on productivity, so professional advice should be sought prior to construction.
Productive topsoil can be beneficial when applied across the clay-base of a pond, but it must be free of pesticides which may be highly toxic to crayfish. Water may be sourced from surface supplies or underground. Generally, water suitable for watering livestock is suitable.
Some of the characteristics which should be identified include;
pH of between 6.5 and 8.0,
hardness of >40 ppm,
low salt content
and low metals content.
Once water has been introduced to the production ponds there are a host of management issues which must be addressed to ensure optimal water quality for redclaw production.
Further information on water quality management should be sought. Water usage is dependent on local evaporation rates, but will range from 15 to 20 megalitres per hectare of ponds. This is on the basis that all effluent from harvested ponds is recycled through appropriate settlement and supply dams.
Varieties/breeds
Research has demonstrated that distinct strains of redclaw occur throughout the species natural range. The differences between strains are generally slight, however, variability of biological characteristics as borne out in production statistics suggests that some strains are superior for aquaculture purposes. Although the full range of strains have not been assessed, it is clear that the Gilbert and Flinders River strains have advantageous characteristics in regard to high fecundity (number of young per brood) and fast growth rates at high densities.
Some long-standing redclaw farmers have selectively bred their perceived 'best' crayfish and cross-bred strains to improve their stock. There are clear indications that these improved stocks are superior to wild undomesticated stock and to stock from farms where managed reproduction has not occurred.
A managed selection program for increased growth rate of redclaw established by the Queensland Department of Primary Industries in 1993, has successfully increased growth rate by about 45 percent to date. This program is continuing and now produces improved 'Walkamin' stock for distribution to industry from the Freshwater Fisheries and Aquaculture Centre at Walkamin.
Animal husbandry
Once all government approvals have been sought and an aquaculture license has been issued, the farmer may acquire crayfish from established growers or from the DPI.
Stock may be purchased as broodstock and used to generate juveniles for stocking to the new operation, or as juveniles for immediate stocking.
The husbandry involved is best explained in terms of the key elements of recognised 'best practise'.
Site selection is the first step, and should involve assessment of several criteria which will maximise the suitability of the chosen site.
A designed and systematic farm layout is important to minimise establishment and operational costs by utilising gravity to fill and drain ponds, and to centralise facilities.
Optimal pond specifications are 1000 sq.m , 1.2 to 2.5 m in depth and a V-shape that allows rapid and complete drainage.
Artificial shelters for the crayfish are essential. They should be abundant, and their shape, specification and positioning should permit water to drain out freely and completely as the pond is drained. Thick bundles of synthetic mesh and/or stacks of pipe material have been found to be the most effective.
Aeration is also essential. For redclaw aquaculture it is most often provided through airlift pumps, although other forms of aeration such as paddle-wheels and aspirators may be used. The aeration system should provide both oxygen input to the water and circulation of water from bottom to top and around the pond.
Juvenile production and growout of stock to market size are managed as separate processes. A managed juvenile production program is essential to provide the advanced juveniles required for growout, and to make effective use of the superior broodstock selected. Depending on temperature and whether berried females or mature broodstock are used, a culture period of 3 to 4 months is necessary to achieve a mean size of juveniles of 5 to 15 g. The two most critical factors in juvenile production are shelter and food.
Growout also involves an active stock management approach. Because redclaw breed so readily and profusely, the pond populations must be managed intensively. This includes stocking with known numbers of advanced juveniles of at least 5 g mean weight. Uniformity of size is very important. Maximum size range at stocking should be 10g. Stocking density of between 5 and 15 per sq.m is recommended.
The food used will have an important bearing on production. Several commercial crayfish pellets are available, which have proven to be effective. Chicken layer pellets are not recommended. The most effective diets have a protein content of approximately 20 percent and are composed primarily of grains. A feeding frequency of once per day is recommended, preferably at dusk when crayfish are active. Use of a feeding schedule and feed trays is critical.
Active management of the pond environment is integral to commercial yields. There should be weekly monitoring of pH, dissolved oxygen and secchi; monthly monitoring of hardness, alkalinity and ammonia. All measurements must be made at the water / soil interface on the bottom, and some contingency plan must be developed to counter water quality which falls outside of preferred ranges. This may involve applications of lime or fertiliser, or flushing of the pond with fresh water.
Drying of ponds between crops is essential to sterilise and re-vitalise the bottom. There is often a considerable build-up of organic waste after a culture period. The most effective management of this is to dry the pond for 1 to 2 weeks until cracks appear. Toxic compounds are broken down and useful nutrients are released.
Protection against birds, rats, and eels, and any other potential predators must be provided. Complete enclosure netting and fencing is essential. Economic analysis indicates that the cost of netting (including materials and installation) is equivalent to about 15 percent of one crop. As losses to predators may be well in excess of this, netting is very cost-effective.
Provided good husbandry practices are applied both processes of juvenile production and growout can be completed within 12 months.
Disease control
Several potentially disease causing organisms including protozoans and viruses have been identified in redclaw.
To date none have caused any significant commercial loss, and industry are aware that careful quarantining and good health monitoring and management will minimise the risk of a disease outbreak.
A virulent disease of crayfish which has decimated production throughout Europe is known as 'crayfish plague'. Australia is free of this disease, and authorities are conscious of the importance of preventing its entry into the country.
By maintaining good culture conditions which maximise survival and growth, stress of crayfish is minimised and the threat of disease is relatively small. Because production of juveniles and growout are contained on each farm, there is little requirement to introduce new, potentially disease-carrying stock to the farm. This factor also diminishes the risk of disease.
Harvest, processing and packaging
Harvesting is generally quite straightforward, however if it is not managed carefully, the previous several months of production management can be wasted.
Some form of sampling prior to harvest is important to gauge the size and number of crayfish expected.
Harvesting may involve a number of methods, although the most effective is the application of a flow-trap. This trap exploits redclaw's strong response to flowing water. A slow but steady flow of water into the pond via a box and ramp will illicit movement of crayfish against the flow and into the box. Flow-trapping should involve 95 percent drainage of the pond over 24 hours from dawn to dawn. There should be several thousand litres of water remaining in the deepest part of the pond at dawn, when stock are removed.
The slow drainage enables the crayfish to move out of shelters and with the main body of water, so they concentrate and respond most effectively to the flow trap. Both the flow trap and the last remaining water must be well aerated. The entire harvest can be easily lost if the flow trap or remaining pond water are not aerated. The stock should be quickly removed and transported to clean water in a tank system.
Care should be taken to minimise crushing by not exceeding 15 kg of stock per transport container.
Other harvesting methods include bait trapping and drain harvesting with manual collection of stock.
The majority of redclaw are sold live, and so after harvesting stock are held in tanks with flow-through water supply or a recirculating system involving biological filtration.
A period of at least 24 hours in the tank to permit purging of the gut is recommended prior to packing for transport.
Redclaw can survive extended periods out of water provided they are kept cool and moist. Packing therefore involves insulated containers containing some moist packing material (foam rubber or wood shavings) and cooling packs.
Road transport is used for local markets, however air transport is necessary to the large seafood markets in Sydney, Melbourne and for export.