The culture of the giant clam (Tridacnidae) for food and restocking of tropical reefs

• James Cook University, Australia

Giant clams are a significant component of the diets of the people of Oceania and Southeast Asia. However, the combined effects of increasing populations, pollution, habitat destruction and poachers have severely reduced stocks of the huge bivalve shellfish throughout its environmental range in the Indo-Pacific. The giant clams grow very fast, and research suggests they can be farmed to produce an estimated 60 tonnes of meat (adductor muscle) per hectare per year. After the first 7 days of life, the clams require only protection, warm seawater and plenty of sunlight in order to grow. Single-celled algae (Symbiodinium sp.), which live in vast numbers in blood sinuses in the mantle tissue, provide nourishment by the process of photosynthesis. International collaborative research has already led to the development of large-scale artificial rearing methods. If remaining restraintssocial, economic and legalcan be overcome to make clam farming feasible in countries of the Pacific, they will benefit substantially.

The first ACIAR project on giant clams (Project No. 8332) culminated in a workshop in April 1988. The 80 delegates were from Southeast Asia and various South Pacific nations, and from commercial, management and research interests in Australia, where clam farming has become a commercial enterprise. This replacement project will build on the earlier one, concentrating on Tridacna gigas where feasible and appropriate, and will address a number of the issues identified at the workshop as requiring further research for establishing a mariculture without demanding technology in developing countries. The objectives of the new project are:

. to undertake farming trials for ocean-nursery and grow-out culture of giant clams with coastal fishing villages;

. to develop management strategies to assist Pacific island countries with stock assessments, management, training and mariculture technology;

. to make further studies of the environmental factors and culture conditions that optimise growth and survival of giant clams;

. to obtain production data and costs for giant clam culture for use in economic analyses and marketing trials;

. to investigate the genetics of the shellfish with regard to geographic variation and the selection of optimal culture traits;

. to determine the normal microflora and pathogenic organisms in field and cultured clams and the pathology of diseased clams; and

. to produce a manual on giant clam stock assessment and mariculture methods.

A range of research methods will be used, reflecting the various objectives of the project. James Cook University will collaborate with three of the overseas institutions from the earlier project and institutions from three additional South Pacific countriesthe Cook Islands, Kiribati and Tonga. Australian technology and information will be developed and transferred to assist the development of the quarantine/hatchery facility at Makogai, Fiji, and to upgrade the hatchery/nursery facilities to increase seed clam production in the Philippines. ACIAR and James Cook University will seek funds to complement their own research activities in the Cook Islands, Kiribati, Tonga and Tuvalu, specifically to develop hatcheries and large-scale nurseries.

The Australian Institute of Marine Science will work with the University of the Philippines on the population genetics of giant clams; and the Oonoonba Veterinary Laboratory will collaborate with the Graduate School of Tropical Veterinary Science of James Cook University to study their diseases.

Giant clam farming does not require highly demanding technology. The project will benefit subsistence farming, where clams are of great importance as a traditional food, and the restocking of reefs. It will also train fisheries personnel and develop mariculture expertise in the Pacific island nations. In the long term, the research will lead to export opportunities and will serve as a model for other developing countries in the tropics wishing to develop giant clam mariculture. In Australia, Aboriginal and Islander communities, which are starting to become involved in giant clam mariculture, will also benefit.