The Derasa Clam is one of the largest members of the Tridacna genus, reaching up to 24” in the wild. Other
common names for this clam include Southern Giant Clam or Smooth Giant Clam. It is closely related to the
Tridacna gigas although they can be differentiated by the number of vertical folds in their shell, with the
Derasa Clam having six to seven. Additionally, only the Derasa Clam can close completely.
They are found in a wide variety of colour combinations in the wild but the aquacultured specimens available
in the hobby trade tend to be orange, brown, gold or yellow with a vibrant blue or green trim on their mantle.
Its shell is smooth, as opposed to the ridged shells of many other clams.
In the wild, they are found broadly across the Indo-Pacific region as well as the Central Pacific and South
Pacific. Unlike many other species of decorative clams widely available in the hobby, the Derasa clam does
not attach itself firmly to the rockwork of a reef. Instead, they prefer to live on the substrate at the edges of the
reef. They are found at slightly deeper depths than many other clams, generally between 10 and 60 feet. They
can live both singly or in colonies and are non aggressive. In a home aquarium they require a substrate where
they can be placed, as attempts to place them in the rockwork will likely be unsuccessful unless there is an
already available recess in the rock. They are photosynthetic and will derive the majority of their energy needs
from aquarium lighting but are less light demanding than many other species of decorative clams. Their
symbiotic relationship with zooxanthellae algae enables this and also provides their colour. They prefer
moderate water flow that is powerful enough to keep them free of detritus but not strong enough to
aggressively agitate their mantle. They are peaceful and can be kept in colonies but some species of angelfish
have been known to nip at their mantles.
The Derasa Clam is a photosynthetic filter feeder. It will obtain the vast majority of its needs from lighting but
will also filter aquarium water for plankton and other organisms. If desired, it can be spot fed with foods
designed for filter feeders and this may be advisable when the clam becomes large.
Aquacultured Derasa Clams are among the largest and most hardy of the decorative clams and can be more
tolerant of mistakes than other species. However, they still require a mature tank with stable parameters in
order to thrive. They make an eye -catching addition to any reef tank and their large size makes them very
suitable as a showpiece specimen.