Clams have become very popular among marine aquarists. Most are of the Tridacnidae family and of the genera Tridacna or Hippopus. These specialized mussels have developed a relationship with the symbiotic algae species Symbiodinium microadriaticum. This algae allows clams to obtain nutrients directly from the sunlight, in addition to the nutrients supplied by gill structure which filters micro-plankton trapped in the water. These clams are found over most of the Indo-Pacific area, and several species are now farm-raised. The adult size of a clam will range from 4 to 48+ inches across. Some live up to 10 years.
Most Clams are found in sandy areas adjacent the reef, though they will inhabit cracks and crevasses in the reef. One species is even capable of boring into limestone. Some species rely on a specialized foot-byssal apparatus to keep them anchored; others rely on their physical weight to stay in place. Once attached by the byssal foot, it is difficult to detach the clam without injuring it.
The most distinguishing feature of clams is their large two-part shell and interior mantle. Their outer mantle has a series of iridophores that are a light-sensing organ. Most have intricately colored patterns in the mantle, making them attractive additions to the marine aquarium. The exact reason for these color patterns is unknown, but is thought to help protect the clam from UV light, and to possibly confuse predators. A healthy clam will have its mantle fully extended beyond the rim of the shell. When shaded, the clam will quickly close to protect itself from predators.
Clams require the best water quality, intense lighting, and usually a moderate current. Strontium and calcium need to be supplemented to maintain growth and the vivid colors. For this reason, they are best for a mature reef aquarium. While clams will occasionally spawn in the home aquarium, success in raising the babies is limited