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Like many bivalues, Tridacnas are filter feeders, straining food items from the surrounding water brought across their enlarged gills by ciliated cells. They also possess zooxanthellae (algae cells) that are found in the fleshy mantle. The clams also derive some portion of their nutrition from the alga.
Photo: Chris Johnson

May 29, 2002
Farming Giant Clams
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Log Transcript

This is Genevieve Johnson speaking to you from the Odyssey in the Cocos (Keeling) Islands.

Throughout much of their geographic range, the seven species of Tridacnas - giant clams, have been heavily exploited. In some parts of Indonesia, the Phillipines, Micronesia and Southern Japan, some of the species are now extinct.

These animals require clean, shallow, warm seawater and plenty of sunlight to survive. Such conditions usually place them in areas where they are accessible to fisherman and easy prey for poachers.

Recognition of globally declining stocks of giant clams prompted Paul Tod to consider the potential for mariculture, a practice that once established is relatively low maintenance with high returns for both the environment and the producer.

Today we were shown around the giant clam farm by Scott Brain:

Giant clams are subject to heavy predation in the wild. Rearing larvae from eggs to juveniles in tanks, protects them from natural predators. Once they have reached 20-200 millimeters in length, they can be reared in the lagoon in protective containers. Once over 200 millimeters they are reared in the lagoon without protection.
Photo: Chris Johnson
Scott Brain:

My name is Scott Brain, I'm a farmer on the Cocos (Keeling) Islands. I grow fruit and vegetables for local production and I also help manage the clam farm.

The two species we grow here are maxima and derasa. The maxima are the smaller size clam and the derasa tends to grow much larger. Primarily, the maxima are being bred and farmed for the aquarium market, while the derasa are being farmed for a meat market.

Basically the clams start life as a microscopic organism, and over a five-year period they grow to a width of between six and ten centimeters at which point they are marketable.

The breeding process involves taking mature clams out of the wild - the lagoon here in Cocos, and putting them into a semi-stressful environment, this may be warm water which tends to torment them a little. The clams then seem to feel the need to pass their genes on, they feel threatened enough that they have to breed.

Giant clams are hermaphrodites, meaning that the male and female parts are in the same animal. The male part produces the sperm and the female part produces the eggs, the eggs are microscopic and once they are fertilized we collect them and deliver them into the hatchery where we keep them for up to two weeks. We then feed them a protein supplement before releasing them into the raceways.

The most lucrative market is the South East Asian market for meat. During the initial lag time of five years in getting ready to produce clams for that market, the aquarium market has been very helpful along the way in terms of cash flow.

Farms such as the one here in the Cocos (Keeling) Islands will assist in replenishing wild stocks of Giant Clams.
Photo: Courtesy of Parks Australia Cocos (Keeling) Islands

Giant clams are not really fairing too well in the wild, for the usual reasons, which include habitat destruction, and over fishing, basically populations are declining worldwide. Certainly in Australia and locally here in the Cocos Islands, the numbers of adults or breeding size animals have really declined.

Genevieve Johnson:

The clam farm here is a wonderfully innovative enterprise. The knowledge being gained is already helping restock this area. As farmers develop clam farming technology further it has the potential for restocking tropical reefs worldwide . And by reintroducing giant clams into areas where they were once plentiful, farmers are providing a source of highly prized protein-once the main protein source for island peoples in both Pacific and Indian Oceans.


Log by Genevieve Johnson

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