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Summary of full report
By Dr Ian W Purvis
April 2006
RIRDC Publication No 06/042 RIRDC Project No CSA-17A
Executive Summary
Water Management – A valuable
commodity for Australian agriculture
The recognition that single-use
systems of water management cannot be sustained when there is a continued
requirement for an expansion of food production on a global basis, has
been a key factor in generating increased interest from governments and
the commercial sector toward the integration of aquaculture and irrigated
livestock production and crop cultivation. A critical resource on most
Australian livestock and irrigation enterprises is the collection of farm
dams and water containment structures. Notions that single-use water strategies
are inefficient and outmoded are becoming more and more prevalent with
today’s farmer and will mean that Australia will see an increasing trend
towards water management being valued on a commercial basis.
Enterprise Diversification
Agricultural producers wishing
to explore aquaculture as a diverse enterprise, are presented with an opportunity
to become more productive and profitable into the future whilst developing
farming systems that will enhance the long term benefits of agricultural
lands for landholders and their communities. Aquaculture will improve the
efficiency of water utilisation on the farm by doubling the use of water,
develop improved productivity and nutrient usage and provide assistance
with reducing the risk of extreme fluctuations in farm income.
Background
With approximately one hundred
freshwater crayfish species found throughout the country, yabbies are Australia's
most abundant native freshwater crayfish. Of these hundred or so species,
three are now farmed in a considerable way. In Western Australia and parts
of South Australia, marron (Cherax tenuiminus), which are native
to the southwest of Western Australia, are farmed in purpose built ponds.
Redclaw (Cherax quadricarinatus) are similarly farmed under controlled
conditions on the coastal areas of Queensland and to a small extent on
the northern NSW coast.
However, the majority of crayfish production currently comes from the yabby (Cherax destructor), which is farmed through NSW, VIC, SA and WA. Although there is enormous variability among wild strains of yabbies and some are more suited to commercial aquaculture than others, they are ideal for farm-based aquaculture.
Primarily omnivorous and an opportunistic feeder, the yabby will feed mainly on rotting vegetation.
Muddy waterways provide protection from predators such as cormorants, herons, ibises and larger fish and invertebrates. Yabbies are tough and can tolerate a wide range of environmental conditions such as poor water quality and differences in water temperatures as low as 1 °C and as high as 35 °C.
Yabbies have been commercially farmed in Australia for over 30 years. However, in this time, there has been no attempt to improve the productivity of commercial stocks through scientifically based selective breeding programs. Growers simply source broodstock from local waterways or from other farms.
In 1999, one kilogram of yabbies could earn a farmer around $6 a kilogram. A bigger, faster growing yabby could increase profit margins considerably. With an ever-increasing interest in yabbies coming from the restaurant trade, an established aquaculture industry able to deliver a constant supply of high quality product to the market could be extremely profitable.
Aims of the Research
The objective of the research
was to establish the best wild strains for aquaculture by discovering the
heritability of desired characteristics, such as fast growth and large
meaty tails. These strains were then selectively bred to develop a strain
of yabby better suited to aquaculture.
Once such a yabby exists in an aquaculture environment, the yabby farmer can better control growth and quality of the livestock, important factors to maintaining a reliable and continuing market for this product.
Methods Used
Superior performing broodstock
yabbies, from various geographic populations, identified by a strain comparison
trial were combined to create a new "commercial" strain and subjected to
four generations of within family selection. Faster growth was the primary
selection goal. At the beginning of the trial the program was based on
the evaluation of 100 full siblings from each of 30 families. Poor survival
of three families reduced the total number in the program to 27. A control
line consisting of randomly bred individuals from the 30 families was also
maintained to allow assessments of genetic gain to be made through selective
breeding.
Results
Of the four generations
of selection, significant differences in mean liveweight at harvest were
observed between select and control lines. The difference represented an
average response to selection in both sexes of 12% per generation and a
realized heritability for liveweight of 30%.
These results demonstrate that response to selection for liveweight in the yabby, Cherax destructor, can be successfully achieved. By selecting within families, significant gains were achieved in generations F2 and F3 that averaged around 15%. Coupled with the initial gains achieved by selecting the F1 founder generation, the select animals in generation F3 grew at 60-70 % faster than the average of all strains taken from the wild to initiate this study.
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