Giant clams: Gems of the reef

The TRIDACNA genus offers roughly five species that are offered for sale in the saltwater aquarium market. Because of their brilliant color schemes and patterns, Tridacnas are becoming more and more popular everyday. T. crocea, T. gigas, T. maxima, T. squamosa, T. derasa and H. hippopus are the common clams for sale on the market. Most of the clams(Tridacna) on the market are captive-bred in large ornamental farms (ie. Walt Smith farms in Fiji). Although some of the clams are wild-harvested, it is much better to aquire a cultured specimen for various reasons. The main reason is that the cultured clams are better suited for the aquarium, due to their easier acclimation. Less time being handled, transported, and accustomed to degrading water quality makes for a cultured clam being a better choice for us avid reefers.

Once a healthy clam has been selected and established in your tank, they are long lived and could last for decades. Of course their are some care requirements for the success of your prized gem.
Tridacna's are largely symbiotic in nature, meaning that they require strong light to survive due to their zooanthellae. The only time that a Tridacna is not reliant on intense light is during their juvenile stage of life, where nanoplankton is necessary for their survival. As far as lighting is concerned, the light requirement for Tridacna clams are the same as that for small polyped stonies. Tridacna's require intense light once they pass through their juvenile stage. The Durasa and Squamosa Tridacna's can be supported under less light than the other Tridacna's with Hippopus and Gigas in the middle then the Crocea and Maxima at the other end of the spectrum.

As with hermatypic corals, Tridacna clams should be placed in a good spot and left there. If they are moved, especially vertically in your tank, you run the risk of stressing them out due to light intensity changes. Then their is also water circulation changes as well as proximity with other inhabitants in your tank.

Your clam's placement within the tank is very important. All the clam species should be positioned at the bottom of your tank in the substrate except for the Crocea and Maxima species. Placment on a hard flat rock, burying the rock in the sand if necessary to reduce the risk of predation through the byssal passage and damage vital organs is recommended.

Because clams are filter-feeders, a fairly strong water flow is important to bring nutrients and carry away waste products. Laminar(one direction) or direct stream water movement is to be avoided as this can offer clams a spiked level of additives and supplements possibly leading to their demise. Random turbulent water movement with a moderate to high turnover of water is to be replicated for the health of your Tridacna.

Feeding of clams is best done with a slow-drip delivery system. Greenwater is an ideal clam food(yeast and cultured phytoplankton). also, a fishless refugium and/or phytoplankton reactor offer natural food sources. Most of the foods offerend to our corals and inverts are not acceptible for clams. These food sources are too big for clams thus rejected from the clam with a sudden expulsion like a cough.

Disolved organics(ie.nitrogen) and nanoplankton(microscopic) are the food with which clams feed. Many times you will see a clam that is pale in comparison to a normal clam may be starving due to low nitrogen levels. Aggressively filtered and skimmed tanks remove such a large amount of nitrogen that endosymbiotic zooanthellae in clams and corals begin to suffer, causing a dull color in your clams appearance. A greater bio-load of fish for example will greatly enhance the clams overall appearance by offereing it more nutrients. Also by keeping your water at roughly 8-12dKH for alkalinity and 350-425 ppm for calcium, you will meet your clams requirements for proper water parameters.

When purchasing and selecting a Tridacna, beyond aesthetics, size is an important consideration. T. gigas can grow up to a half an inch a month and become several feet in length and a few hundred pounds in a few years. Whereas, a T. duras, squamosa and H. hippopus reach impressive sizes as well, though top out at about two feet in length. T. corcea is the smallest species usually averaging about six inches in length.

As a rule, purchasing very small or very big Tridacna's offers but the slimmest of odds for success in an aquarium due to shipping, handling and acclimation as mentioned above. You are best seeking intermediate sized clams in the 3-5" range as they tend to be stronger with regards to the stresses involved with captivity.

Clams have many pests and predators associated with them. Boring sponges, Pyram, Murex and ostellarid snails, segmented and flat worms and various crabs prey on such clams. Routine inspection of your clam is of utmost importance for the success of your clam in captivity. Many predators can be captured by baiting a bare bottomed qt with pieces of clam offered for sale in the local pet shop freezer.

When selecting a clam, make sure that its mantle(colored fleshy lobe extending to and above the shell) is extended, colorful, dark and crisp, meaning that their is a healthy population of zooanthellae. Also, make sure that your clam is alert and responsive to light changes. The best way to do this is to place you hand between the clam and the lighting above causing a shadow. The clam should close up promptly to such disturbance. If this doesn't happen, it usually means that the clam is stressed and should be frowned upon as a possibly purchase. Also, a "GAPPING" clam indicates a serious and often fatal problem. A larger than normal stretching appearance of the the inhalant siphon(large opening in the mantle) or of the clam's shell halves is the last stage before death in many clams.

In concluding, anyone that want to venture into the realm of adding a Tridacna to their reef environment, should do some research. They should also have an established tank(atleast 8 months). Start off with a more hardy species like the Durasa and Squamosa. Make sure that they do checks to make sure their are no predatory problems. Check their water parameters and make corrections very slowly. Make sure to place the clam in one spot and leave it to eliminate possible stress on your clam.

Remember that Tridacna clams are a beautiful addition to any reef tank. The intense colors and patterns offer a nice flavor to any tank these vivid gems of our reef...;D