Maxima clam

Care at a glance

Overview

The Maxima clam is a peaceful, reef-safe giant clam for a brightly lit reef tank, where it sits high on the rockwork. It is a step up from the easier clams, best for a keeper with a little reef experience.

Caring for the Maxima clam

The Maxima clam is one of the more demanding clams to light correctly. Give it strong, stable light, equal to what a small-polyp stony coral would need. Set it on a secure perch on live rock, high in the tank and close to the light, rather than on open sand. It needs a tank of at least 40 gal (150 L).

It byssal-attaches to rock within a day or two of settling in. Treat that first attachment point as permanent, since forcing it loose again tears the byssal gland.

Calcium, alkalinity and magnesium all need to stay elevated and stable, since the clam pulls hard on all three to keep building shell. Typical targets are calcium at 380 to 450 ppm, alkalinity at 8 to 11 dKH and magnesium at 1280 to 1350 ppm. Keep the water at 75 to 81°F (24 to 27°C) with a pH of 8.1 to 8.4.

Larger clams get most of their energy from light alone. Specimens under 5 cm rely more heavily on filter feeding, so give them a phytoplankton or greenwater supplement a few times a week.

Watch for mantle-nipping tank mates, since some wrasses, crabs, shrimp and pyramid snails will pick at the exposed flesh. Introduce a new clam gradually, floating it to match temperature and drip acclimating it slowly. Start it in a shadier spot for the first couple of weeks before moving it up into full light.

Good to know

Tridacna maxima belongs to the family Cardiidae, subfamily Tridacninae. It is best told apart from other Tridacna by its elongated shell with widely spaced, uneven scutes. Its mantle never fully retracts, so color still shows even when the clam pulls in tight. Like other giant clams it carries millions of photosynthetic zooxanthellae in its mantle tissue. Specialized iridescent cells called iridocytes scatter and redirect light deeper into the tissue, keeping the algae fed even in the shaded folds. The clam uses the sugars and energy the zooxanthellae produce to help lay down its calcium carbonate shell. All Tridacnidae, including this species, are listed under CITES Appendix II, so international trade in live clams or shells requires an export permit.

In the wild

The Maxima clam lives on shallow reef flats and lagoons across the Indo-Pacific and Red Sea, from East Africa to French Polynesia. It is one of the two widest-ranging Tridacna species, alongside the squamosa clam. It usually lives in water less than 6 meters deep, where light is strongest. It wedges itself into a hole or crevice in coral rock and spins byssal threads from its foot to anchor there for life. Only the colorful mantle and shell edge show above the rock.

Common questions

Related species

• 

  Squamosa clam

  Tridacna squamosa

  15.7 in (40 cm) · 40 gal (150 L)

  15.7 in (40 cm)40 gal (150 L)75–81°F (24–27°C)

• 

  Squamosina clam

  Tridacna squamosina

  11.8 in (30 cm) · 66 gal (250 L)

  11.8 in (30 cm)66 gal (250 L)75–82°F (24–28°C)

• 

  Noah's clam

  Tridacna noae

  9.8 in (25 cm) · 40 gal (150 L)

  9.8 in (25 cm)40 gal (150 L)75–81°F (24–27°C)

• 

  Derasa clam

  Tridacna derasa

  19.7 in (50 cm) · 40 gal (150 L)

  19.7 in (50 cm)40 gal (150 L)75–81°F (24–27°C)

• 

  Crocea clam

  Tridacna crocea

  5.9 in (15 cm) · 30 gal (115 L)

  5.9 in (15 cm)30 gal (115 L)75–81°F (24–27°C)

• 

  Gigas clam

  Tridacna gigas

  47.2 in (120 cm) · 198 gal (750 L)

  47.2 in (120 cm)198 gal (750 L)75–81°F (24–27°C)