Tridacna derasa (Derasa Clam) Care Guide
Tridacna derasa is a large smooth-shelled giant clam from the Indo-Pacific, hosting zooxanthellae and tolerant of more moderate light.
Compiled by Aquairi from published sources · Published · Updated
Overview
Tridacna derasa, the smooth or southern giant clam, reaches up to 60 cm in length. It is named for the relative lack of ribbing and scales on its thick shell, which shows six to seven vertical folds and lacks scutes. The mantle displays mixtures of orange, yellow, black and white, often marked with brilliant blue or green lines.
Taxonomy
- Family: Cardiidae
- Subfamily: Tridacninae
- Genus: Tridacna
- Scientific name: Tridacna derasa
Habitat
Its native range includes Australia, the Cocos Islands, Fiji, Indonesia, New Caledonia, Palau, Papua New Guinea, the Philippines, the Solomon Islands, Tonga and Vietnam. It is found on the outer edges of reefs at depths of about 4 to 10 metres.
Tank requirements
- Minimum tank volume: 400 L
- Temperature: 24-26 C (75-79 F)
- pH: 8.1-8.4
- Carbonate hardness (KH): 8-11 dKH
- Calcium: 380-450 ppm
- Magnesium: 1280-1350 ppm
- Specific gravity: 1.024-1.026
- Lifespan: 50-100 years
Diet
The species hosts symbiotic zooxanthellae that photosynthesise, allowing the clam to obtain nutrition from the water column beyond standard filter feeding. As a larger clam it tolerates more moderate lighting than crocea or maxima, while still benefiting from stable calcium, alkalinity and magnesium for shell growth.
Compatibility
It is peaceful and reef-safe among reef fish. Mantle-nipping species such as angelfish, triggers and pufferfish should be avoided.
Conservation status
IUCN Red List: Vulnerable. The species is listed on CITES Appendix II. It has been heavily harvested for food and the aquarium trade, although modern supply relies largely on aquaculture rather than wild collection.
Breeding the Derasa Clam (Tridacna derasa)
Overview
Tridacna derasa is one of the largest giant clams, reaching about 60 cm, with a relatively smooth shell bearing six to seven vertical folds. It is native to Indo-Pacific waters and has been reintroduced to several locations including Guam and the Marshall Islands. It harbors zooxanthellae that photosynthesize and supply nutrients, and it tolerates lower light than crocea or maxima. It is listed as Vulnerable by the IUCN and on CITES Appendix II.
Sexing
Like other giant clams, T. derasa is initially male and later becomes a hermaphrodite possessing both male and female reproductive organs. Individuals cannot be reliably sexed externally, and spawning depends on several mature clams releasing gametes together.
Conditioning
Stable reef water with adequate light for the zooxanthellae and proper calcium, magnesium and alkalinity supports growth. In hatcheries, broodstock are conditioned and then induced to spawn; breeding typically occurs in spring and summer, although spawning can be induced year-round.
Spawning & Larvae
As a broadcast spawner, the clam releases sperm and eggs separately to prevent self-fertilization, with fertilization occurring in the water column. Fertilized eggs develop through trochophore and veliger stages before settling, after which juveniles acquire zooxanthellae from the surrounding water. The MMDC hatchery in Palau pioneered commercial breeding of this species, making it among the first clams produced at large commercial scale.
Common Challenges
- Home reefs do not supply open-water spawning cues or larval conditions.
- Free-spawned gametes and planktonic larvae are lost to filtration and predation.
- Settled juveniles must acquire zooxanthellae from the environment.
- CITES Appendix II listing regulates international trade.