Derasa Clam

Photo: Wikimedia Commons (CC BY-SA)

Tridacna derasa

Identification	One of the larger Tridacna species with a smooth, relatively unadorned shell. Mantle coloration tends toward browns, greens, and golds with repeating stripe or spot patterns. Shell margins are smoother with fewer pronounced ridges. Often called the Southern Giant Clam or Smooth Giant Clam.
Maximum Length	20 inches (50 cm); most aquarium specimens are 4–10 inches
Origin	Indo-Pacific — Australia, Indonesia, Fiji, Tonga; found on deeper reef slopes at 5–20 feet depth
Minimum Tank Size	75 gallons; more tolerant of moderate lighting than Maxima or Crocea
Reef Compatibility	Yes — completely reef safe

Behavior

The Derasa Clam is considered one of the hardiest and most forgiving Tridacna species for the home aquarium. Unlike Maxima and Crocea, it does not bore into substrate and prefers to sit freely on a sandy bottom or flat rock. It is less light-demanding than smaller Tridacna species, adapting well to moderate reef lighting due to its natural habitat on deeper reef slopes. Grows relatively quickly under good conditions.

Diet & Feeding

Photosynthetic — moderate to high reef lighting (150–250 PAR) is sufficient. Supplement with phytoplankton dosing. Passive filter feeding on dissolved organics provides additional nutrition.

Cautions

Grows large — plan for adult size. Protect from mantle-nipping fish. Although less light-demanding than other Tridacna, still requires reef-quality lighting.