The culture of the giant clam (Tridacna spp) for food and restocking of reefs

• University of the Philippines, Philippines
• Ministry of Primary Industries, Fiji
• Silliman University, Philippines
• University of Papua New Guinea, Papua New Guinea

Giant clams form a significant component of the diets of the people of Oceania and Southeast Asia, being completely edible except for the kidney. The adductor muscle is a highly prized food in Southeast Asia. However, the combined effects of increasing populations, pollution and habitat destruction and the depredations of poachers have severely reduced stocks of these tridacnid clams throughout their Indo-Pacific distribution. Apart from large size, giant clams are notable for maintaining symbiotic algae in their exposed fleshy mantle tissue, which supply them with photosynthetic products. Thus clams are phototrophic, with similar environmental requirements to plants, and are the only potential farm animals that feed themselves. Some species grow rapidly and current studies suggest that annual production rates of 60 tonnes of clam meat per hectare are considered quite feasible.
If they could be cultivated, tridacnid clams would add substantially to the supply of low-cost, locally produced acceptable protein food, simultaneously providing a high-value exportable product in the form of dried adductor muscle. Research work done to date on the maricultural possibilities of giant clams, although fragmentary and on a small scale, has not revealed any major impediments to commercial-scale cultivation, but further research is necessary. The largest living species, Tridacna gigas, grows rapidly to as much as 137 cm, which makes it a prime target for additional research. The known extinction of T. gigas and Hippopus hippopus in some areas, the threatened status of these and other species elsewhere and the consequent or threatened loss of genetic diversity provide additional justification for substantial research effort.
This project has five main objectives. The scientists will assess tridacnid stocks at various localities in Fiji, Papua New Guinea and the Phillipines, using standardised field assessment procedures. Secondly, they will study natural growth rate of tridacnids and the influence that environmental factorsespecially those related to latitude such as water temperature, sunlight intensity, tides etc.have growth. Thirdly, they will investigate the reproductive biology or tridacnids, including gametogenic and spawning cycles and spawning chemistry. A fourth goal is to identify the specific ecological requirements of larvae and juvenile clams in natural and experimental extent of protection necessary for juveniles and also for adults. Finally, the scientists will apply the results obtained in the above research to establish the hatchery and rearing techniques for optimum growth and survival rates in large-scale culture of the tridacnid species of greatest commercial importance.
At the same time, an investigation by the International Centre for Living Aquatic Resources and Management (ICLARM) will undertake a complementary research program on socio-economic, processing and other technical topics, which will include development of a hatchery and grow-out facility in a representative equatorial Indo-Pacific island environment.
In addition to increasing the protein food supply in Oceania and Southeast Asia, extensive clam mariculture would reduce the pressures leading to over-exploitation of coastal fish stocks in Pacific waters. Harnessing the tropical reef, the greatest natural resource of the Pacific Islands, would be a strong incentive to preserve the marine environment and would highlight the benefits of conservation.