Why is my Derasa Clam not opening fully?

A clam may refuse to open if it is not receiving adequate lighting, if water parameters (like calcium and alkalinity) are unstable, or if it is being harassed by nipping fish or parasitic pyramidellid snails.

Does the Derasa Clam need to be placed on a rock?

No, it is highly recommended to place Derasa Clams on a sandy or rubble substrate. They grow very large and heavy, and placing them on rockwork risks them falling and sustaining fatal shell damage.

How quickly do Derasa Clams grow?

They are among the fastest-growing giant clams and can add several centimetres of shell length per year under optimal lighting and with stable calcium and alkalinity levels.

Do I need to feed my Derasa Clam phytoplankton?

While adult clams derive most of their energy from photosynthesis, small clams (under 5 cm) benefit greatly from supplemental target feeding with high-quality phytoplankton.

Are they safe with all reef fish?

No. Many fish, such as large angelfish, butterflyfish, and pufferfish, will nip at or entirely consume the clam's fleshy mantle. They must only be housed with completely reef-safe, peaceful fish.

MarineMarineIntermediate

Derasa Clam

Tridacna derasa

A spectacular, fast-growing giant clam celebrated for its smooth shell and strikingly patterned mantle.

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Ideal Conditions

Temperature: 24 – 28 °C
pH range: 8.1 – 8.4
Hardness: 14 – 22 dGH
Salinity: 1.023 – 1.026 SG
Adult size: 50 – 60 cm
Large reef aquarium: 400 litres+
Lifespan: 20 – 40 years
Diet: Photosynthetic and filter feeder
Water flow: Low to moderate
Preferred setup: Deep sand bed or rubble bottom

About the Derasa Clam

The Derasa Clam, often referred to as the Smooth Giant Clam, is one of the most widely kept and hardiest species of the Tridacna genus. Unlike its highly textured relatives, it features a relatively smooth, scute-free shell as it matures. Its real draw is the expansive fleshy mantle, which exhibits dazzling waves of gold, orange, blue, and green, providing an incredible focal point for large marine aquariums.

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Where Derasa Clam comes from

Native range

Indo-Pacific, Great Barrier Reef

Countries / regions

Australia, Fiji, Indonesia, Philippines, Solomon Islands

Habitat

Sandy or rubble-strewn margins at the base of coral reefs, typically in shallower, sunlit waters.

Widely cultured in aquaculture facilities for the aquarium trade, reducing pressure on wild populations.

Similar species

Maxima Clam
Tridacna maxima
Crocea Clam
Tridacna crocea
Squamosa Clam
Tridacna squamosa

We’re adding more full species guides as the catalogue grows.

Compatible tank mates

Reviewed guidance based on this species' recorded traits.

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Ocellaris Clownfish
Amphiprion ocellaris
Peaceful reef fish that will completely ignore the clam and occupy higher water levels.
Great
Yellow Tang
Zebrasoma flavescens
Herbivorous tangs help keep algae off the clam's shell without damaging the mantle.
Great
Bicolour Blenny
Ecsenius bicolor
May attempt to perch on the clam's shell or nip at the mantle, causing the clam to stay closed and slowly starve.
Compatible with caution
Coral Beauty Angelfish
Centropyge bispinosa
Dwarf angelfish are notorious for nipping at the fleshy mantles of giant clams.
Not recommended
Dogface Puffer
Arothron nigropunctatus
Pufferfish possess powerful beaks designed for crushing and eating molluscs, making the clam a highly likely meal.
Not recommended

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