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. ShelterArtificial 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. GrowoutGrowout 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. Pond MaintenanceDrying 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. |