Breeding the Maxima Clam (Tridacna maxima)
Tridacna maxima is the most widely distributed giant clam, a broadcast-spawning sequential hermaphrodite. It does not reproduce in home reefs but is propagated by induced spawning in aquaculture facilities.
Overview
Tridacna maxima has the widest range of all giant clam species, found from East Africa and the Red Sea through the Indo-Pacific. Large specimens typically reach about 20 cm in shell length, making it much smaller than the true giant clam. It obtains most of its nutrients from symbiotic zooxanthellae, so it requires intense reef lighting. It is listed on CITES Appendix II, requiring permits for international trade in all parts and derivatives.
Sexing
T. maxima is a sequential hermaphrodite: an individual matures into a male after two or three years and becomes a hermaphrodite when larger, at around 15 cm in length. Individuals cannot be reliably sexed externally, and reproduction relies on groups of mature clams spawning together.
Conditioning
Strong reef lighting for the zooxanthellae and stable calcium, magnesium and alkalinity for shell growth keep the clam healthy. In aquaculture, broodstock are conditioned under optimal conditions before spawning is induced; a home display sustains the animal but does not trigger reproduction.
Spawning & Larvae
Spawning is triggered by the lunar cycle, time of day and the presence of eggs and sperm in the water. To prevent self-fertilization, the hermaphroditic clam releases its sperm first, followed later by its eggs. A fertilized egg hatches within about 12 hours into a free-swimming larva, develops into a filter-feeding form and then gains a foot; after 8-10 days metamorphosis produces a juvenile clam able to acquire zooxanthellae. Hatcheries reproduce this sequence under controlled conditions.
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 in clams and their derivatives.