Derasa Clam Care Guide: Tridacna Derasa Hardy Giant for Reef Tanks
If you want the grandeur of a giant clam without the demanding light requirements of a maxima, Tridacna derasa is your answer. The derasa clam is widely regarded as the hardiest and most forgiving of the Tridacna species commonly kept in reef aquariums, making it an excellent entry point into clam husbandry. This derasa clam care guide from Gensou Aquascaping at 5 Everton Park, Singapore is grounded in over 20 years of reef-keeping experience and covers everything from initial placement to long-term growth management.
Species Profile
Tridacna derasa is the second-largest giant clam species, capable of reaching 50-60 cm in shell length in the wild. Aquarium specimens typically top out at 25-35 cm over many years, which is still substantial. The mantle displays wavy, gold, brown and green patterns, generally less vivid than maxima or crocea clams but attractive in its own understated way. Occasionally, specimens with blue or turquoise mantles appear, and these command higher prices. Like all Tridacna clams, derasas harbour symbiotic zooxanthellae and derive most of their nutrition from photosynthesis.
Why Derasa Is the Beginner’s Giant Clam
Several factors make derasas more forgiving than their relatives. They tolerate moderate lighting, with PAR values of 150-250 being adequate — far less than the 300-plus required by maximas. They grow quickly, adding 5-10 cm per year under good conditions, which means small specimens reach a robust size relatively fast. Their tolerance for minor parameter fluctuations exceeds that of other Tridacna species. None of this means derasas are low-maintenance — they still need stable reef conditions — but the margin for error is genuinely wider.
Lighting and Placement
Moderate to high lighting suits T. derasa well. A quality LED fixture providing 150-250 PAR at the clam’s position supports healthy zooxanthellae activity. Full-spectrum lights with emphasis on the blue wavelengths (420-480 nm) produce the best mantle colouration. Unlike maxima clams, derasas naturally rest on sandy substrates rather than attaching to rock, so placement on the sand bed is perfectly acceptable and often preferred. Position the clam in a stable spot where it will not be toppled by flow or other tank inhabitants. Avoid placing it directly beneath the highest-intensity light spot if your fixture produces over 300 PAR — gradual acclimation to higher light prevents mantle bleaching.
Water Chemistry
Standard reef parameters keep derasas healthy: specific gravity of 1.024-1.026, temperature of 24-27°C, pH of 8.1-8.4, alkalinity of 8-11 dKH, calcium of 400-450 ppm and magnesium of 1280-1350 ppm. These clams build shell at a significant rate, so calcium and alkalinity consumption is noticeable, especially with larger specimens. Monitor these parameters weekly and dose accordingly. Singapore’s soft PUB tap water, when processed through an RO/DI unit, provides an excellent blank canvas for mixing reef-grade saltwater without unwanted contaminants.
Feeding
Photosynthesis through zooxanthellae supplies the bulk of a derasa’s energy. Supplemental feeding with phytoplankton benefits smaller clams under 10 cm and accelerates growth across all sizes. Broadcast live or preserved phytoplankton into moderate flow near the clam two to three times per week. The incurrent siphon draws in particles when the clam is actively filter feeding. Do not overfeed — excess phytoplankton degrades water quality. In a well-lit, mature reef with natural plankton production, large derasas often require no supplemental feeding at all.
Growth and Space Planning
Derasa clams grow faster than most hobbyists anticipate. A 7 cm specimen can reach 20 cm within two to three years under optimal conditions. Plan for this growth when choosing placement — a clam wedged between rock structures will eventually outgrow the space and may suffer shell deformation. Open sand areas with unobstructed light access work best. In an HDB flat or condo setup, ensure your tank and stand can support the additional weight as the clam grows, as a 30 cm derasa with its shell weighs several kilograms.
Health Monitoring
Healthy derasas display a fully extended mantle with good colour saturation. The shadow response — a quick retraction when a hand passes overhead — indicates a well-functioning nervous system. Persistent gaping, where the shell remains open with the mantle retracted, signals stress or illness. Check for pyramid snails (Pyrgiscus spp.) by inspecting the shell at night with a torch. These tiny parasitic snails feed on clam mantle tissue and can weaken even large specimens over time. Manual removal and periodic freshwater dips of the shell (not the mantle) address minor infestations.
Purchasing in Singapore
Derasa clams are available at marine-focused shops across Singapore, typically priced at $40-120 SGD depending on size and colour. Aquacultured specimens from Palau and Tonga are increasingly common and generally acclimate better than wild-caught stock. When selecting, verify the shadow response and examine the mantle edges for signs of pinching or recession. Transport home quickly and acclimate via drip method over 60-90 minutes. Placed in a well-maintained reef with adequate lighting, a derasa clam becomes a centrepiece that grows more impressive with every passing year.
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