The 1995 review of world aquaculture resources by the Food and Agriculture Organisation identified the major constraints to future development of aquaculture as being: the availability of feed ingredients; disease and health management; environmental impacts; and genetic and diversity issues. There are two areas in which genetics is especially important in aquaculture development: 1) Appropriate broodstock selection and breeding programs for the genetic improvement of important production traits; 2) Genetic implications of the translocation of aquaculture stocks within and outside their natural range.
Genetic improvement: The power of selective breeding in increasing productivity and efficiency has been amply demonstrated in traditional agricultural species. Aquaculture species have hardly benefited from modern developments in animal breeding, despite their typically high reproductive capacity and therefore high potential for genetic improvement. The key issues which need to be addressed are the appropriate traits for improvement and their genetic parameters (heritability, correlations with other traits); optimal selection methods (mass selection, family selection, construction of selection indexes); avoidance of inbreeding; and the role of recombinant DNA technology (transgenesis, marker-assisted selection and cytogenetic manipulation).
Understanding the power of genetics is particulary important with aquaculture species where egg supply is a limiting factor. This applies to many fish species where the first generation bred in captivity often become the broodstock for the industry. Accidental initial selection of a slow growing strain (compounded by inbreeding), or starting with a small genetic base often leads to an uncompetitive industry.
Translocation: The issue of translocation is likely to become an increasingly important constraint upon aquaculture development. Although policy guidelines are currently being produced in Western Australia and other states, their application will be hampered by a lack of genetic knowledge on two fronts. Firstly, we know very little about the genetic population structure of most endemic potential aquaculture species. Secondly, what we do know comes almost entirely from studies of neutral genetic markers, and may bear no resemblance to the genetic structure of traits of ecological importance. The issues that need to be addressed are: laboratory and analytical techniques for measuring population genetic structure; relating population genetic structure to genetic variance in traits of ecological importance; the effects of breeding for stock enhancement on inbreeding and variance effective population sizes.
These issues of genetic improvement of breeding stock and genetic effects of translocation are two sides of the same coin, because the traits which we wish to improve through breeding are in most cases precisely those traits which determine the adaptedness of local populations to their environment. Both issues need to be addressed at this early stage in the development of the aquaculture industry in Australia.
Restocking of native fish stocks is also becoming increasingly important in Australia as the political power of recreational anglers and the value of their sport to local economies increases. Restocking programs should not be undertaken without an understanding of the genetic structure and variance of existing populations or the knowledge needed to ensure that the restocked fish do not alter this balance.
Final report
Aquaculture in Australia is a rapidly growing industry. More than 60 aquatic species including crustaceans, molluscs, finfish, crocodiles and microalgae are presently cultured in Australia, although less than ten species support around 80% of the total value of the industry. In 1995, a review of world aquaculture resources by the Food and Agriculture Organisation identified genetic and diversity issues as major constraints to the future development of aquaculture. There are two areas in which genetics is especially important in aquaculture development: (1) the genetic improvement of important production traits; and (2) genetic implications of the intentional movement (translocation) of organisms for aquaculture or restocking programs.
Genetic improvement of aquaculture species offers substantial opportunities for increased production efficiency, disease control, product quality and ultimately profitability for aquaculture industries. Most aquaculture industries in Australia are at an early stage of development and would benefit from the introduction of genetic improvement programs.
The first step in a genetic improvement program is to determine which traits should be improved (the breeding objective), and find measures for those traits (the selection criteria). Size at harvest is perceived by industry participants, managers and researchers as the trait that will most influence profitability for all major aquaculture species in Australia. Other traits of general importance are survival to harvest, disease resistance (especially in edible molluscs), meat yield and feed conversion efficiency. For some aquaculture species, such as trout, there are good estimates of the heritabilities and genetic correlations among these traits, and studies are beginning for a number of crustacean and mollusc species. In most cases, however, we still lack the basic information needed to define effective selection criteria for the traits we wish to improve.
Once the breeding objective and selection criteria have been determined, we need to consider the methods by which superior breeding stock will be selected. Mass selection, where breeding stock are chosen on the basis of individual performance, is most common in aquaculture species. This may lead to inbreeding, however, because individuals with superior performance will often be closely related. One method of overcoming this is by taking the performance of relatives into account when choosing breeding stock (family selection). The major research priority for genetic improvement across all aquaculture species in Australia is the development of genetic markers to enable accurate pedigree determination. This would allow the more widespread use of family data in selection decisions, without costly maintenance of separate family lines until individuals can be physically marked.
The major constraint upon the implementation of genetic improvement programs by aquaculture industries is lack of available funds and resources. Many aquaculture industries in Australia are small and immature, and uncertainties over production costs and market opportunities limit investment in long-term genetic improvement programs. Ensuring industry ownership of genetic improvement programs, and national coordination among researchers, are vital in all aquaculture industries. Government support may be necessary in the early stages of development, and the favourable benefit:cost ratio demonstrated, for example, by the Norwegian breeding program for salmonids, should encourage the targeted investment of public funds into genetic improvement programs for aquaculture species.
