Maxima clam (Tridacna maxima) care guide

Group

Other invertebrates

Other names

Small giant clam, Rugose giant clam, Elongate giant clam, Tridacna elongata, Tridacna compressa

Family

Cardiidae (subfamily Tridacninae; often listed as Tridacnidae)

Origin

Indo-Pacific and Red Sea, the widest range of any giant clam; aquarium stock now mostly farmed in the central and South Pacific

Water

saltwater

Maximum size

30 cm

Temperature

22–26°C

pH

8.1–8.4

Hardness

dKH 8–11, SG 1.023–1.025

Minimum tank

200 litres

Care level

intermediate

Reef safe

yes

Lifespan

10 or more years

Flow

Medium to strong, not blasting the mantle

Care

The maxima clam is the most popular giant clam in the hobby, prized for its brightly coloured mantle in blue, green, gold, brown or patterned forms, the colour coming from light-reflecting pigment cells. Its shell is elongated and uneven with closely spaced scales, typically under 20 cm, though LiveAquaria gives up to 30 cm in the wild. It lives on reef tops and sand, or partly buried in coral, and anchors itself with byssus threads. 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. Light: it hosts symbiotic algae (zooxanthellae) in its mantle that supply most of its food, so it needs very strong reef lighting, of the kind used for SPS corals. Place it high in the tank or on rock once acclimatised. Clams of 5 cm or less are more delicate; start them low or in a dish on the sand and raise them gradually over a few weeks. Placement: it attaches to rock or rubble within a day or so, so treat its first spot as permanent. Never pull an attached clam off, because tearing the byssus causes fatal injury; if you must move it, cut the threads close to the rock with a razor blade. Water: LiveAquaria gives 22–26 °C, pH 8.1–8.4, SG 1.023–1.025, calcium 380–450 mg/l, alkalinity 8–11 dKH and magnesium 1280–1350 ppm, with good flow. Watch for pyramidellid snails, tiny white parasitic snails that feed on clams at night; check the shell edges with a torch after dark and remove them. Copper: copper-based medicines and some plant fertilisers are toxic to shrimp, snails and most other invertebrates. Never treat a tank holding them with copper, check the label of any fertiliser or medicine, and keep nets and buckets used for copper-treated tanks separate. Sources: LiveAquaria (liveaquaria.com/products/maxima-clam-blue-aquacultured); Wikipedia (en.wikipedia.org/wiki/Tridacnamaxima). Checked October 2026.

Diet

Mostly fed by its zooxanthellae under strong light. It also filter-feeds on phytoplankton. Clams over 5 cm need no extra food in a normal reef; smaller clams in very clean tanks benefit from phytoplankton a few times a week.

Breeding

Maxima clams start life as males at 2–3 years and become hermaphrodites at about 15 cm. Spawning is set off by the moon, time of day and eggs or sperm in the water; sperm is released first, which avoids self-fertilisation. Eggs hatch within 12 hours into swimming larvae, which settle and change into juveniles after 8–10 days. Farms raise them in large numbers, which is why captive-bred clams are widely available; they are not bred in home tanks.

Compatibility and tank mates

Reef safe, but it needs space: corals must not sting or shade it. Fish such as some angelfish, butterflyfish, puffers and triggers nip the mantle, and some wrasses and hermits may pick at it. Pyramidellid snails and bristle worms can attack weak clams.

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