Giant clam (Tridacna gigas) care guide

Group
Other invertebrates
Other names
True giant clam, Gigas clam, Chama gigantea
Family
Tridacnidae
Origin
Indo-Pacific shallow coral reefs, from the Indian Ocean to the South Pacific, South China Sea and Philippines; to about 20 m
Water
saltwater
Maximum size
137 cm
Care level
expert
Reef safe
yes
Lifespan
100+ years
Flow
Moderate

Care

Tridacna gigas is the true giant clam, the largest living bivalve. It averages about 120 cm across and over 200 kg, and the largest recorded shell measured 137 cm. Wild clams can live more than 100 years. It lives on sand and coral rubble on shallow reefs. Several other giant clams (T. derasa, T. squamosa, T. maxima, T. crocea) are often mistaken for it; most clams sold for home aquaria are those smaller species. Light: like other giant clams it hosts symbiotic algae (zooxanthellae) in its mantle and opens by day to expose the mantle to light. The algae provide around 65–70% of an adult's food, so it needs strong, reef-grade lighting, placed on the sand or rubble low in the tank as it grows. Small clams depend more on filter feeding. In the aquarium: captive-bred juveniles are occasionally offered, but this species grows fast, around 12 cm a year in culture, and soon outgrows almost any home tank, so it only suits very large systems or public aquaria. Keep stable reef parameters with good calcium and alkalinity for shell growth. Our sources give no water figures. Selling: giant clams are listed on CITES Appendix II. Captive-bred clams can be sold freely in the UK; imported clams must have been legally imported with CITES paperwork. Overharvesting for food and the aquarium trade has wiped it out in some areas, including peninsular Malaysia. Copper: copper-based medicines and some plant fertilisers are toxic to shrimp, snails and most other invertebrates. Never dose them in a tank holding this animal, and check the label of any treatment or fertiliser before use. Sources: Wikipedia (en.wikipedia.org/wiki/Tridacnagigas). Checked October 2026.

Diet

Mainly fed by the zooxanthellae in its mantle under strong light; it also filters fine particles, and small clams get a larger share of their food this way. Juveniles benefit from occasional fine phytoplankton foods. Keep nitrate and phosphate low but not zero.

Breeding

Each clam is a hermaphrodite but cannot fertilise itself. Clams spawn into the water, triggered by a chemical signal from neighbours and linked to tides and moon phases; one adult can release over 500 million eggs. Larvae settle after about a week. Mass culture in Palau and Australia (James Cook University, Orpheus Island) supplied clams for restocking. Not bred in home aquaria.

Compatibility and tank mates

Reef safe, but needs space and light. Angelfish, butterflyfish and some puffers pick at the mantle; pyramidellid snails and bristleworms can attack young clams. Keep clear of stinging corals.

Last updated 8 October 2026. Community-edited care guide on Aquatic-Auctions.

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