There is a need for marron aquaculture to follow the example of traditional agriculture and develop domesticated varieties, rather than continuing to rely upon unselected wild stock. In fact, current husbandry techniques on commercial farms, in particular harvesting practices, are likely to result in the selection of slower growing marron for future broodstock (i.e. through early marketing of fastest growing individuals with broodstock chosen from the residual population), as is the case in yabby farming (Lawrence et al. 1998).
Investment in marron farming has grown rapidly in WA and SA with medium term potential of 1000 t p.a. ($20 million) in WA and 250 t pa ($6.25 million) in SA, based on current investment (conservatively $15 million in WA), anticipated expansion at these farms, performance of better farmers, and site availability (marron are grown from Geraldton to Esperance). As volumes increase the current excellent ex farm prices for marron ($16-32/kg) may decline and necessitate improved production efficiency. Consultation with industry has identified growth rate and size variation as the main factors affecting profitability of marron farming. Industry’s belief in the need for this research is reinforced with significant cash ($9000 from WA) and in kind contributions.
There is a need to i) compare production of farm stock with that of their ancestral populations to determine the effects of current farm management practices upon marron gene pools, ii) compare different wild stocks to identify the best marron strain for farming, and then iii) genetically improve the best strains
Just as traditional agriculture has increased growth rates of livestock and poultry by strain evaluation and selective breeding, there is a need to achieve similar gains with marron by developing a genetically improved strain which will result in greatly improved profitability for industry.
In addition, there is considerable debate amongst consultants and farmers as to what are the best methods for producing marron. While experimental trials have shown yields may be increased, demonstration and documentation of the "best practice" marron farming system has not been undertaken. There is a need for husbandry improvements that can both increase the quantity and improve the quality of farmed marron. The issue of improved quality is vital to farmers, as marron are exported alive but industry currently report mortality rates of up to 11%. Reducing mortality by ensuring marron being sent to market are in top condition will have clear and measurable improvements in profitability. With industry we have developed this proposal which combines the needs of industry with the proven freshwater crayfish expertise of Fisheries WA researchers along with facilities and expertise in animal breeding from the University of Western Australia. South Australian farmers and researchers are keen to extend such research activity and results to that state. To facilitate this the project involves SA industry, SARDI, PIRSA and the University of Adelaide.
Final report
Marron (Cherax tenuimanus) are the highest valued freshwater crayfish farmed in Australia. This project addressed the need to increase the profitability of commercial marron farms by improving growth rates and pond management strategies.
The project evaluated progeny produced from wild populations collected from 6 river systems that had not been subjected to the broodstock selection processes on commercial farms. This demonstrated that current management of broodstock, whereby farmers sell the largest crayfish produced and breed from remaining animals, has resulted in slower growth of marron on commercial farms. Marron from all river systems grew faster than industry stocks. The best performing wild river strain, from the Harvey river, grew 82% faster than current industry stocks.
A simple mass selection selective breeding program improved growth rates by 86 -110% in two generations.
Consultation with farmers identified breeding objectives that were applied by researchers to develop a selection index for a more complex pedigree breeding program that permitted simultaneous selection for multiple traits based upon economic merit. This program also permits greater control of inbreeding than mass selection.
Husbandry experiments showed that current refuge densities were suitable for marron production. Paddlewheel aeration practices could be improved by increasing the duration of aeration. Relaying juveniles produced early in the year in northern regions did not improve final production. Size grading of juveniles prior to stocking ponds can, however, increase the average weight of marron harvested by 12 - 58% and decrease the proportion of below market size animals by 54%.
Marron with proportionately shallower abdomens grow faster than those with deeper abdomens. Combined with hide harvesting, this simple condition index can be applied by farmers to evaluate condition of marron in commercial ponds, calculate growth rates and manage feed rates.
Farms based in the more southern, cooler regions, have lower growth rates due to cool water temperatures. In this study the best region from a temperature perspective is Pinjarra, where lower water temperatures limit growth for only 0.6% of the year, compared to the least favourable region, where temperature limits growth for 33% of the year.
It is essential that commercial marron farms are correctly designed, constructed and professionally managed. Commercial trials involving 147,000 marron reared to market size in 44 commercial ponds over a 5 year period demonstrated the viability of current practices and the increased profit ($33,600/ ha) from farming selectively bred marron developed in this project.
An extension strategy that included open days, research seminars, field trials and open communication with industry was extremely successful. Most key outputs from this project have already been adopted by leading farmers with newer entrants to the industry following their example. As a result the husbandry strategies and software developed by this project have been rapidly adopted by industry and 18,000 elite marron produced from the selective breeding program have been distributed to industry in WA and SA.
The use of marron produced by the FRDC selective breeding program dramatically increases the profitability of farming. For a correctly managed and constructed 50 pond farm replacing industry stock with marron from the selective breeding program increases the IRR from 8.24% to 22%, return on capital from 4% to 40%, yields from 1.5 to 3 t/ha/year and profit from $20,722 to $189,130 /year.
Keywords: Marron, Cherax tenuimanus, genetics, husbandry, aquaculture, hides, aeration.
