Redclaw,Cherax quadricarinatus, is a species of freshwater crayfish native to tropical Queensland and the Northern Territory. They occur predominantly in the rivers flowing into the Gulf of Carpentaria and some easterly flowing rivers of northern Cape York Peninsula. Unlike other species of freshwater crayfish, the adult male redclaw has a distinct soft red patch on the outer margin of the claws, hence the name redclaw. Redclaw have a host of biological characteristics that make them a very suitable candidate species for aquaculture.
Culture environment The natural habitat of the redclaw, the turbid billabong that is flushed during the wet season, does not provide the best environment for farming. Commercial production only occurs in purpose built facilities rather than farm dams. Although redclaw are able to tolerate environmental extremes, commercial growth rates can only be sustained where water quality is high. One of the most important site selection parameters is temperature, and the site should maximise the period where temperatures are above 23°C
Breeding and juvenile production Breeding activity is dependent upon water temperature and daylength, and normally occurs between September and April within their natural range. A protraction of the breeding period can easily be achieved by providing a controlled environment in which temperature is manipulated to simulate the onset of the breeding season. Techniques for breeding and juvenile production vary considerably between farms and regions. Generally, selected broodstock (some redclaw strains are clearly superior for cultivation over others) are placed in specially designed ponds or tanks where mating naturally occurs.
The female broods the eggs for 6 to 10 weeks, depending on temperature. The larger the female, the more eggs she can produce. Most females produce between 300 and 800 eggs per brood. Redclaw may produce between 3 to 5 broods during the breeding season. Hatchlings resemble the adult form and remain attached to the underside of the female for several weeks before progressively becoming independent of the mother. Advanced juveniles are normally harvested at 5 to 10 grams (3 to 4 months old) and sorted for size and sometimes sex.
Growout Commercial growout is normally undertaken in earthen ponds, which usually range from 1000 m² to 1200 m²with sloping bottoms (1.3 to 1.8 metres deep) to facilitate drain harvesting. Similar sized juveniles are stocked in prepared ponds at 5 to 15 animals per m². The stock and pond water is carefully managed so as to maximise growth and animal health. The total growout time is approximately 6 to 9 months (plus the 3 to 4 months spent in the juvenile production pond). Stock is often harvested progressively due to differential growth rates. Several market size grades exist from 35 grams to over 100 grams.
Adults are generally non-aggressive and non-burrowing when adequate habitat and nutrition is provided. An abundance of suitable shelter increases the survival and growth potential of the animal. Feeding of formulated pellets is often supplemented by a mixture of grains to provide a basic food base for the animal, although much of the nutritional requirements can be obtained from natural pond production (eg. plankton, bacteria, protozoans, etc.). This natural production can be enhanced by organic and inorganic fertilisation, providing that ammonia and oxygen levels remain within the acceptable range. Feeding is normally undertaken 3 times a week just before dusk to coincide with the animal’s peak foraging behaviour. Some form of aeration is normally installed (usually airlift pumps) to increase the carrying capacity of the ponds.
Harvesting Several harvesting techniques, used independently or in conjunction with each other, are employed. These include bait trapping, drain harvesting and flow trapping. Flow trapping is the most successful technique, and utilises the animal’s natural behaviour. A current of water is directed into the pond through a ramp. This solicits a response from the crayfish and they move into the current, up the ramp and into a harvest box. After harvesting, the best crayfish are selected as broodstock, with the majority of the production being sold. Broodstock selection ensures that individuals displaying desirable characteristics, such as fast growth rate, are able to contribute their genes to the successive generations. In order to effectively manage the pond environment and the stock of redclaw within the pond, it is essential that every pond be entirely drained and dried, at least once each year.