Breeding the Derasa Clam (Tridacna derasa)
Tridacna derasa is a large giant clam and one of the first species bred commercially. It is a broadcast-spawning hermaphrodite that does not reproduce at home but is widely aquacultured for the trade.
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.