A R2R Spotlight "Tridacna Derasa"


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May 8, 2009
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lovely rainy NW Washington
Genus = Tridacna
Species = Derasa
Common name= Derasa clam

Size and growth rate
T. Derasa The Derasa Clam is also referred to as the Southern Giant Clam or Smooth Giant Clam. The latter name refers to the relative lack of scutes on the shell. The smoothness of its thick shell, and the 6-7 vertical folds helps to differentiate its species from T. gigas, its larger relative which is not as smooth and has 4-5 folds. In our aquariums, however, scutes may develop on the Deresa Clam due to the non hostile environment and the scutes not being broken off. This species is one of the largest of the "giant" clams, and grows rapidly, reaching a maximum size of approximately 18 inches. Under the proper conditions, smaller Derasa Clams can double or triple their size in less than a year. Those in the aquarium trade are usually cultured.

Location and geographic range
This gentle giant can be found living amongst corals and or on sand and rubble. The Derasa can be found living as deep as 15 meters. T Derasa can be found in the Indian Ocean, from Cocos-Keeling Island to the Central Pacific Ocean from Fiji, to Tonga. They are also found north to south from the China Sea, the Philippines down to the Great Barrier Reef and central Australia.

Attachment to substrate
As juveniles, T. Derasa uses their a byssal organ that secretes the sticky threads that will attach it to the substrate. This helps keep the clam from being swept away. In time this organ atrophies, the byssal opening grows shut with shell, and the large size of the animal helps keeps it in place.

Lighting and flow requirements
Derasa are one of the least light demanding of all the giant clams, even though they still require high end light. They will probably be ok with VHO or compact fluorescent lights but I recommend metal halide or T5 with individual reflectors. Giant clams are found on reefs that usually have SPS corals, flow should be moderate to high. Just be sure that the mantle isn't being held over un naturally because of too much flow.

Derasa's mantle are a mixture of orange, yellow, blue, and black and white, and usually has a wavy striped or spotted pattern, usually with vivid blues and greens.

Reef compatibility
Giant clams are found among the reefs of the world and are compatible with most reef safe animals. Although there are some reef safe fish that are not clam safe. These include: Angelfish, some Wrasses, Blennie's, Eels, and some shrimp.

Conclusion and comments.
Derasa's are common to the aquarium industry. T. Derasa is a very hardy species and a good clam for the beginning hobbyist, provided reasonably strong lighting, clear water conditions and stable salinity is provided..

It is my personal opinion that if you intend to keep a Tridacna Derasa you should have an aquarium of 75 gallons or larger. They can be kept in smaller tanks but they rapidly outgrow them.
Top Shelf Aquatics


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May 8, 2006
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Bump for input and photos!


Where's the mysis?
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May 27, 2012
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South Jersey



Coral Fraud Private Eye
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Jun 4, 2011
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Marshall, TX
I got one a few years ago about 2 1/2 inches. It's pushing 7 now and grows fast if my water is right. If I don't see a thick line of new shell I know something is wrong with my water. I've never fed phyto or anything like that, even when small.

Mid 2010 IIRC,

July 2012

I havn't taken a pic in a while but the same clam is in the bottom right of the tank,

It's big enough now that when it closes up quickly you can hear it in the tank and all the fish scatter.


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Mar 26, 2013
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San Antonio, TX
I had never kept a clam before, but I decided to take the plunge about 5 months ago. Love this guy!




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Apr 2, 2013
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Rochester, NY USA
I've been trying to get a clam specific tank setup this year and have not had any luck for some reason. I had multiple of every type (squamosa, crocea, maxima, derasa, hippoppus) yes they have all withered away or attacked by bristle worms. I've had clams previously that lasted over 8 years but now the oldest clam I have is only 1 year old. Just don't know what's wrong. My system is gear for SPS and acropora specifically thrives in my system. Maybe my system is just way too clean? Even dose nitrates.

Any special reefing plans for this week?

  • Yes

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