Derasa clam (Tridacna derasa) care guide

Group

Other invertebrates

Other names

Smooth giant clam, Southern giant clam, Derasa giant clam

Family

Cardiidae (subfamily Tridacninae)

Origin

Western Pacific and eastern Indian Ocean around Australia, Indonesia, the Philippines, Palau, Fiji and Tonga; outer reefs at 4–10 m

Water

saltwater

Maximum size

60 cm

Temperature

22–26°C

pH

8.1–8.4

Hardness

dKH 8–12, SG 1.023–1.025

Care level

intermediate

Reef safe

yes

Flow

Moderate, indirect flow

Care

The derasa clam, or smooth giant clam, is one of the largest giant clams, reaching 60 cm. Its thick shell is smooth, without the scales of most other Tridacna, and has six or seven folds. The mantle is usually patterned in wavy stripes or spots of orange, yellow, black and white, often with blue or green lines. It is one of the hardiest and fastest-growing giant clams in the hobby, and most derasa sold today are farm-raised; it was one of the first giant clams bred commercially, notably in Palau. Like all giant clams it hosts symbiotic algae (zooxanthellae) in its mantle, which turn light, carbon dioxide and nitrogen into food for the clam. Light needs (general hobby guidance, not from our sources): derasa tolerate moderate light better than crocea or maxima clams, but still need good reef lighting; place them on the sand or a stable rock low in the tank, never in shade. Acclimatise new clams to strong lights gradually. Keep it in a mature reef tank with stable calcium, alkalinity and magnesium, as it builds a heavy shell. Water figures here are standard reef conditions. Because it grows large, plan for a big tank. Clams are vulnerable to pyramidellid snails and to fish that nip the mantle; inspect new clams for tiny parasitic snails, especially at night. Do not keep clams in tanks treated with copper. 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. Wild derasa are considered threatened by the IUCN because they have been heavily harvested for food and the aquarium trade, so choose farmed or captive-bred clams. Copper-based medicines and some plant fertilisers are toxic to shrimp, snails and most invertebrates. Sources: Wikipedia (en.wikipedia.org/wiki/Tridacnaderasa). Checked October 2026.

Diet

Most of its food comes from its symbiotic algae, so light is its main 'food'. It also filters fine particles from the water and absorbs dissolved organic compounds. Small clams under about 5 cm benefit from occasional phytoplankton or fine particulate foods; larger clams in a mature, fed reef usually need no direct feeding.

Breeding

Derasa clams mature first as males and become hermaphrodites about a year later. They release sperm and eggs separately to limit self-fertilisation, usually in spring and summer, although hatcheries can induce spawning all year. The larvae later take up zooxanthellae and settle. Breeding is done in commercial hatcheries, not home aquaria.

Compatibility and tank mates

Reef safe and harmless to fish and corals, though nearby corals may sting it if placed too close. Avoid angelfish, butterflyfish, puffers, triggers and some wrasses that nip the mantle, and watch for pyramidellid snails and bristle worms attacking stressed clams. Do not place where rocks can fall on it.

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