Redclaw is a species of freshwater crayfish native to the westerly and northerly flowing rivers of Queensland's Gulf of Carpentaria, the easterly and northerly flowing rivers of the Northern Territory and also the southerly flowing rivers of Papua New Guinea. Redclaw is very similar to the marron (Cherax tenuimanus), and the yabby (Cherax destructor spp.) and all three have attracted significant commercial interest within Australia and internationally.
The majority of yabbies sold within Australia come from managed farm dam fisheries in Western Australia, South Australia and Victoria. Marron and redclaw however, are cultured in specifically constructed semi-intensive aquaculture ponds. Total freshwater crayfish production for Australia in 2000/01 was around 400 tonnes, while global production was around 70,000 tonnes. Clearly there is scope for export marketing.
The Northern regions of Australia show a distinct wet/dry seasonality, and as such the water bodies that redclaw inhabit vary with season, from fast flowing rivers in the wet, to billabongs throughout the dry periods. These billabongs are frequently highly eutrophic, having poor water quality, and progressively diminish in size as the water evaporates. Crowding leads to a greater competition for food and shelter. Redclaw has evolved to tolerate a relatively high population density and poor water quality conditions, making it a highly attractive aquaculture prospect.
Since the early 1980s there has been very broad interest in redclaw crayfish aquaculture. Industry pioneers were quick to learn of the species’ positive aquacultural attributes, such as fast growth rates, ease of reproduction, lack of any free-living larval stages, gregariousness, and the ability to tolerate poor water quality conditions. That interest stimulated research which led to the development of optimum husbandry and best practice techniques. Even so, the redclaw farming industry in Queensland has not lived up to early expectations and predictions, and production has remained relatively low. There are very few licensed redclaw growers in the Territory.
Since its inception, the redclaw farming industry has slowly emerged to its current level of 86.3 tonnes of official production in the 2000/01 fiscal year. This is despite the report of Treadwell et al. Showing redclaw as a species with great commercial potential at the time, and the economic analysis by Hinton and Jones which showed an internal rate of return of 29.09% and a discounted payback period of only four years. The economic model of Hinton and Jones had a set up cost of $329,000 which may be prohibitive to some investors. The cost of setting up a stand-alone 5 ha redclaw aquaculture business in the Territory is as yet unknown.
There were in excess of 220 redclaw aquaculture licences in Queensland in 2000/01, covering 150 ha of ponds. The majority of licensees are hobby farmers and their poor yields contribute significantly to the industry average. In reality there are fewer than 20 farms producing in excess of 1,000 kg of product annually, and of these the average yield is 1,600 kg/ha. The best of these farmers are producing between 3,000 and 5,000 kg/ha.
The harsh climatic and geographical conditions that redclaw crayfish has evolved in, have facilitated the development of broad tolerances to physical extremes. The prevailing conditions of billabongs in the Territory can be very extreme with wide variations through the day. Typically, these billabongs will have quite poor water quality with low levels of dissolved oxygen and low alkalinity, wide daily pH and temperature swings, and high nutrient loads. To make matters worse the billabong will diminish in size as the water evaporates in the dry season, leading to further crowding, higher nutrient loads and reduced food and shelter resources. These factors have combined to mould a crayfish that is tolerant to poor water quality conditions and relatively high population densities. This species is therefore relatively non-aggressive, and it is also able to utilise a wide range of food resources efficiently.
Queensland strains of redclaw grow well over a broad temperature range. Optimal growth occurs between 26 and 29°C with lethal limits estimated to be around 9-10°C and 34-35°C. This broad range of optimal growth is probably typical for redclaw over its natural distribution, although the strains from around the Darwin region may be more tolerant to higher temperatures. Little research has been conducted on the Territory strains of redclaw. A wide tolerance for temperature variation also indicates that the species may be farmed over a wide section of the Territory.
Tolerance to salinities as high as 12 ppt for extended periods has also been established for this species. This is advantageous for two reasons. Firstly, aquaculture in mildly brackish water may be possible, and secondly, a final purging in salt water prior to marketing can be performed if markets request it. Generally freshwater crayfish is marketed as a premium seafood product with a delicate flavour for a refined palate.
Redclaw is able to survive under conditions of very low dissolved oxygen (1 part per million (ppm) which can result in poorly managed aquaculture ponds. If dissolved oxygen in the pond water drops below 1 ppm, redclaw will move to the edge of the pond where oxygen levels are generally higher, and in extreme cases will migrate from the pond over land. It is comforting to know that redclaw will survive under conditions that would otherwise kill other species, but for maximum growth, and good economic returns, it is important that ponds are managed in accordance with best practice protocols including good water quality management.