Horse Hoof Clam

Care at a glance

Overview

It wants moderately high, stable reef lighting, a bit less exacting than a maxima or crocea but still well above what a low-light coral would need. Calcium, alkalinity, and magnesium should stay elevated and consistent, calcium at least 380 to 440 ppm, alkalinity 8 to 11 dKH, and magnesium 1280 to 1350 ppm, to support its notably thick, heavy shell. Give it a stretch of open sandbed rather than rockwork, since adults are not byssally attached and simply rest in place. Juveniles under about 8 cm benefit from a phytoplankton or greenwater supplement a few times a week on top of what they get from light. Because its mantle sits flush with the shell rather than draping over the edge, it offers less exposed tissue to mantle-nipping wrasses, crabs, shrimp, and pyramid snails than a Tridacna clam does, though it is not immune and should still be watched. Acclimate a new arrival slowly, floating to match temperature, drip acclimating over an hour or more, and giving it a lower-light spot for the first week or two before moving it into full light.

In the wild

Lives on shallow reef flats, seagrass beds, and sandy lagoon floors across the Indo-Pacific, most commonly around Indonesia and Palau. Juveniles briefly byssal-attach to solid substrate, but adults sit free in loose sand or rubble rather than staying fixed to rock the way most Tridacna do. In the aquarium it wants an open sandbed with room to sit, not a rock perch.

Good to know

Hippopus hippopus sits in the family Cardiidae, subfamily Tridacninae, in its own genus alongside just one other species, and its thick, heavily ridged shell carries the strawberry-red blotches that give it its other common name. The clearest way to tell it apart from a true Tridacna clam is the mantle itself: it stays flush with the shell margin and never overhangs the edge the way a maxima or derasa mantle does. It still hosts photosynthetic zooxanthellae and depends on them for most of its energy and shell-building, and it carries the same CITES Appendix II protection as every other giant clam, with the IUCN listing it as vulnerable due to overharvesting across parts of its range.

Did you know

Unlike the mostly ornamental trade pressure on other giant clams, this species has historically been fished hard as food across the Pacific and Southeast Asia, with its meat sold fresh in local markets, and that subsistence harvest, more than the aquarium trade, is the main reason wild populations have crashed in several countries.

Related species

• China Clam

  Hippopus porcellanus

  15.7 in (40 cm)106 gal (400 L)75–81°F (24–27°C)

• 

  Maxima Clam

  Tridacna maxima

  13.8 in (35 cm)40 gal (150 L)75–81°F (24–27°C)

• 

  Squamosa Clam

  Tridacna squamosa

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

• 

  Derasa Clam

  Tridacna derasa

  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)75–81°F (24–27°C)

• 

  Gigas Clam

  Tridacna gigas

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