Genetic improvement of cultured tilapia and redclaw species in Fiji and Australia

• Ministry of Agriculture, Fisheries and Forests, Fiji
• Queensland Department of Primary Industries, Australia

Tilapia is a fish type particularly suited to subsistence-level fish farming. The technology for breeding and maintaining these fish in culture is well developed, and the necessary conditions are fairly basic. However, the fish is also suited to more sophisticated, market-orientated commercial culture programs.
Tilapia have high reproductive and growth rates, they resist disease, and can tolerate water of quite poor quality. In addition, they require minimum management and energy inputs. However, their productivity is limited in certain common conditions. For example they can reproduce precociously and reach stocking rates that are too high, resulting in poor quality specimens; they can also hybridise too readily with related wild fish.
To avoid these drawbacks, strains must be selected and tailored for the culture conditions encountered in each situation. Aquaculture is a relatively new industry in Fiji, but its development is important to ensure future protein requirements on the islands. Already about 180 fish farms are operating, Fijians have shown a liking for eating tilapia, and the Government has committed itself to expanding the industry and developing improved stock.
Aquaculture is also quite new in Australia. Although some species (such as salmon, oysters and prawns) are now cultured, the potential remains to do much more. Much of the biology and genetics of aquatic species remains unknown. Aquaculture using the redclaw crayfish (Cherax quadricarinatus) has grown rapidly, with annual production in Queensland now more than $1 million, and this research explored its considerable potential for domestication and stock improvement.

The aim of this project was to develop improved breeds of tilapia in Fiji and of redclaw crayfish in Australia. It followed earlier ACIAR-funded research to evaluate existing tilapia species in Fiji and identify the most suitable breeds for genetic improvement. This current project also aimed to strengthen the research and extension capabilities of fisheries staff in Fiji, particularly in areas relevant to genetic improvement programs for aquatic species.

The project assessed Fiji's best-performing strain of tilapia against the specially 'improved' strain from the Genetic Improvement of Farmed Tilapias (GIFT) developed in an ICLARM program. The researchers selected across three generations of the best strain, and developed and applied techniques for strain identification using the markers found in micro-satellite DNA. This work ensured that the GIFT strain was properly assessed for its ability to meet Fiji's requirements prior to importation. The project also developed extension procedures to ensure effective dissemination of knowledge about genetically improved breeds and their requirements.
In Australia, the project used redclaw tissue samples to identify genetic markers for use in any future selection programs. The work also documented the levels and patterns of genetic variation.

Stock improvement programs were developed for both tilapia in Fiji and for the redclaw crayfish in Australia. In Fiji the GIFT strain was imported into the country under quarantine conditions and evaluated in replicated trials against the best performing 'indigenous' tilapia strain (Chitralada). Performance of the GIFT fish under a variety of culture environments in Fiji was superior to the indigenous tilapia strain and so the GIFT fish was selected to replace Chitralada as the strain of choice for Ministry of Agriculture, Fisheries and Forests (MAFF) hatcheries to provide to commercial farmers. Both farmer and consumer response to the new strain has been positive, and improved growth rates and higher survival have promoted the development of tilapia aquaculture and improved the financial and social positions of many poor farmers.
A second introduction of the GIFT fish to Fiji was instigated late in the project to guard against future problems with low effective population sizes (Ne) resulting from chance loss of a number of the GIFT families during the evaluation period. The MAFF hatcheries now routinely provide fingerlings from this introduction to commercial farmers without cost. Demand has increased significantly for the fry and tilapia aquaculture has expanded with the development of new hatcheries in other regional areas on the two large islands. Some small farmers have been so successful that they are now diversifying into other culture species (freshwater prawns and carp) and/or integrating fish culture with vegetable production. In a number of instances farmers have purchased additional land to develop new ponds.
A second objective of the Fiji subprogram was to improve the capacity of MAFF aquaculture staff to undertake stock improvement projects on aquatic species. MAFF aquaculture staff received short-term training in handling, breeding and tagging of improved tilapia strains (by the GIFT Foundation in the Philippines) and in experimental design and analysis for aquaculture research projects (by Queensland University of Technology (QUT) staff in Fiji). The manager of the MAFF Aquaculture Research Station completed a research Masters in Applied Science in the School of Natural Resource Sciences at QUT in 1998, developing advanced skills in stock improvement by testing the potential of mass selection to improve colour quality of a Fijian hybrid red tilapia strain.
The Australian component, designed to improve stock of the farmed redclaw crayfish, involved the QUT, Queensland Department of Primary Industries and CSIRO Tropical Agriculture working together. A redclaw experimental culture stock with improved growth rate was developed at Walkamin Research Station through a combination of within- and between-family selection.
In parallel research molecular markers were developed at QUT with the assistance of CSIRO collaborators, enabling researchers to document genetic diversity in wild and cultured redclaw stocks. This molecular analysis indicated clearly that genetic diversity is extensive in wild stocks, but to date little of this has been exploited in culture stocks - most of which have been developed from limited sampling from only a small number of major river systems in the southern Gulf of Carpentaria. Genetic data also indicate a clear distinction between 'eastern' and 'western' redclaw wild stocks. It appears that the stocks have taken significantly independent evolutionary paths, suggesting that future culture stocks may need developing independently in the two regions and translocations among them restricted.
The improved stocks are being evaluated on a number of commercial farms in north Queensland. During the time frame of this project, the redclaw culture industry expanded in northern Australia to a point where it can now benefit from these improved culture stocks.