Growing & Harvesting Redclaw
The redclaw (Cherax quadricarinatus) is a species of freshwater crayfish native to tropical Queensland and the Northern Territory. Redclaw have a host of biological characteristics that make them a suitable species for aquaculture. They grow quickly, breed naturally in ponds and have a simple life cycle.
Breeding activity for redclaw depends on water temperature and day length, and normally occurs between September and April within their natural range. Farmers can protract breeding 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 6-10 weeks, depending on temperature. The larger the female, the more eggs she can produce. Most females produce 300-800 eggs per brood. Redclaw may produce 3-5 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 5-10g (3-4 months old) and sorted for size and sometimes sex.
Commercial growout is normally undertaken in earthen ponds, which usually range from 1000m² to 1200m² with sloping bottoms (1.3-1.8m deep) to facilitate drain harvesting. Similar sized juveniles are stocked in prepared ponds at 5-15 animals per square metre. The stock and pond water is carefully managed to maximise growth and animal health.
The total growout time is about 6-9 months (plus the 3-4 months spent in the juvenile production pond). Stock is often harvested progressively due to differential growth rates. Several market size grades exist from 35g to over 100g.
Like all crustaceans, redclaw moult or shed their shell as they grow. Immediately after moulting, redclaw have soft shells and are vulnerable to predation by other crayfish in their pond. Providing shelter increases the survival and growth potential of farmed redclaw. The best forms of shelter are mesh materials, such as onion bags or shadecloth, and short lengths of pipe.
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.
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 (e.g. plankton, bacteria, protozoans). This natural production can be enhanced by organic and inorganic fertilisation, as long as ammonia (<0.05mg/L) and oxygen levels (>5.0mg/L) remain within the acceptable range.
Redclaw farmers use several harvesting techniques, either independently or together. 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. In order to effectively manage the pond environment and the stock of redclaw within the pond, it is essential to drain and dry every pond at least once each year. 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.
The primary diet should include plant matter, worms, brine shrimp, bloodworms, or insect larvae, and can include vegetable matter waste from aquaponic systems such as lettuce, shredded carrots, zucchini, etc.. Adding a high protein fish or shrimp sinking pellet, flake food, and dried algae is also recommended.