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A Brief Guide to the Selection and
Placement of Tridacnid Clams

A Brief Guide to the Selection and Placement of Tridacnid Clams

By Barry Neigut

James Fatherree and Barry outside the latter's business, Clams Direct

Do you want to dress up your reef tank by adding a Tridacnid clam?  If you're like many reef hobbyists, the answer is a resounding "Yes!"

Before you run out to buy that prized Tridacnid clam, there are several things that you need to consider.

First of all, make sure that your aquarium has been established long enough to support the needs of your new addition. A good indication of your aquarium’s suitability for Tridacnids is a nice growth of coralline algae. Such growth usually occurs 6 months to a year after your aquarium has been established.

Make sure that your fish and invertebrates are compatible with Tridacnids. Some cleaner wrasses have proven to be destructive to clams, nibbling on their mantles and otherwise preventing full expansion. Other fishes may also  harass clams. For example, I once had a Copperband Butterfly that was introduced into an established aquarium that contained clams. It never bothered the clams at all, until one day I placed a few new clams into the aquarium and he attacked them within moments. Observation and careful selection of fishes is critical if you tend to be successful with clams. 


Another important consideration is proper lighting.  Some clams require intense lighting to maintain their long term health and color.  Such lighting is most effectively and economically provided by metal halide lamps. The wattage and number of lamps required depends upon the dimensions of your system and the species that you intend to keep.  Suffice it to say, in most aquariums with a depth of 20" to 30", a 175 - 250 watt metal halide lamp per square foot will do a great job.  In aquariums less than 20” deep, you could also utilize compact fluorescent (PC) and VHO bulbs.  Keep in mind that the different species will dictate the lighting requirements. For example, Tridacna crocea and Tridacna maxima require more intense lighting than the other species.  Smaller Tridacnids, and those with brown mantles do not require as much light as those with colorful mantles.

Bulb temperatures of 6,500K-10,000K are ideal, and will provide the spectrum the clams need for growth, and will help maintain optimum coloration in the animals.

Water Chemistry

New Growth Visible at the Shell Margin

Along with proper lighting, water chemistry plays an important role in health of Tridacnids.  The water chemistry should be stable, with no large swings in your specific gravity or pH.

Here are some recommended environmental parameters:

  • Salinity  1.022 - 1.025

  • pH  8.0 - 8.4

  • Alkalinity  9.0 - 11.0 dKh

  • Calcium  400ppm+

Calcium  and alkalinity (carbonate hardness) are the building blocks of Tridacnid shells and should be measured on a regular basis and maintained at the levels listed above. The growth of a juvenile clam is readily evident on the upper margin of the shell, and is a good indicator of the health of the clam. Poor growth of clams is a good indication that something is wrong in the system, and in most cases caused by a lack of available calcium or carbonates.

Calcium is not the only element that is needed by clams for proper growth. Some hobbyists choose to add iodine supplement to their clam tanks because the believe that iodine helps detoxify excessive oxygen radicals produced by symbiotic algae. If you plan on supplementing iodine, be sure to test the water on a regular basis to avoid overdosing which may lead to nuisance algae and other potential problems within the aquarium. Many aquarists believe that enough iodine is added inadvertently through feeding and water changes since iodine is present in both good quality salt mix and in most aquarium foods.

Many other trace elements are important to clam health, but trace element solutions are easily overdosed. Most trace elements can be safely and easily maintained through regular partial water changes. I strongly believe that doing small water changes on a frequent basis is better than larger water changes on a less frequent basis since trace elements will be added more often. Partial water changes have the added benefit of reducing pollutants. 

Some beautiful specimens of Tridacna maxima


Now that you’ve created the right environment, it’s time to choose that beautiful specimen for your aquarium. Let's take a look at some of the ways to be sure you are getting a healthy and attractive specimen.

When examining Tridacnids, make sure that the mantle extends well over the shell.  Also, the clam should show a healthy response behavior to stimuli. This is done by placing your hand between the light source and the clam. This should cause the clam to close quickly and re-open after a few moments.

Clams generally appear more attractive when viewed from the top than they do when viewed from the front of the aquarium. Many times, the colors will brighten when you place them under more intense lighting, and could fade under inadequate lighting.  Do keep this in mind when evaluating a prospective Tridacnid for purchase.

Check to see if there is any “bleaching” or white areas on the mantle. This normally appears between the incurrent and excurrent siphon.  Sometimes, this bleaching will appear brown or “washed out” in color, but don’t mistake a gold color as bleaching. The gold clam pictured above is not bleached.

Pyramidellid  Snails

Inspect the clam around the mantle and “byssus” (foot) to make sure there are no Pyramidellid (“Pyram”) snails. These parasitic snails can do serious damage to the clam and must not be allowed into your aquarium. Make sure that you carefully examine the specimen for the presence of jelly-like sacks which house the eggs of these snails. Several dozen snails can hatch simultaneously.  If Pyramidellids are discovered in your aquarium, there are a few fish that will help in controlling them, such as Coris formosa, Coris gaimard, and the popular Sixline Wrasse, Pseudocheilinus hexataenia. Manually removing these pests at night (when they are feeding) may also be necessary.

Look for “gaping,” a condition in which the animal’s shell is completely open, the mantle poorly extended, and the incurrent siphon appears to be stretched. In most cases, this is caused by some form of stress. This is often caused by shipping, and in most cases will cease after a few days. Having kept and shipped thousands of clams, I have noticed that Tridacna crocea displays this condition more commonly than other Tridacnids. However, Tridacna crocea seems to recover from the condition whereas it is cause for concern in Tridacna maxima.

Check the shell to make sure it is not broken, and that the mantle is not torn or ripped.  Do not purchase an animal that displays any signs of damage.

Prior to purchasing your clam, ask if the specimen was collected in the wild or if it was cultured. Usually cultured clams are easier to keep and maintain.  One of the potential problems with wild-collected clams is the collection process itself.  Improper collection techniques can result in serious damage to the clam, particularly the byssal gland. Carefully inspect your prospective purchase to assure that the byssal tissue is not torn or hanging from the specimen. This damaged tissue can result in the development of a bacterial infection that caused the clam to die.

If at all possible, find out how long the clam has been in the dealer’s inventory. Ask your dealer if you can purchase it and leave it in his/her tank for a few days longer. This extra time will allow you to observe the clam and make sure that no infections or other maladies manifest themselves before you take the animal home.

Tridacna squamosa

Tridacna crocea


After you bring your clam home, you will need to acclimate it to your water conditions before placing it in your aquarium. This should be done slowly so as not to stress the clam. New aquarium water should be added to the bag or container holding the clam a small amount at a time until the water volume has doubled. This process should take at least an hour.

Clams must also be acclimated to new lighting. Place the animal in a dark tank and let it acclimate to your lighting regime. You can then gradually increase your lighting time over the course of a few days until you reach your desired exposure time. Keep the clam facing upward toward the light so that the full mantle is exposed to the light source. We do not want part of the mantle to become bleached or lose zooxanthellae.

I recommend that newly introduced clams be placed at the bottom of the tank for about a week while deciding where to place it permanently.  This will also give the animal time to adjust to both your water and your lighting.  

Tridacna derasa, Tridacna squamosa, and Tridacna gigas are best placed on sandy substrate, whereas Tridacna crocea and Tridacna maxima should be placed in the rock work. Take notice of the currents in your aquarium, because most Tridacnid clams do not like strong water movement. Tridacna maxima and Tridacnid crocea can tolerate relatively stronger currents.

Another concern when placing Tridacnids is to consider what other animals are in close proximity to your chosen location. You don’t want to put the clam where it can be stung by any extended sweeper tentacles from resident corals. 

Wild bright colors aren't required to make a clam beautiful, sometimes an amazing pattern will catch your eye!

If your ideal location for your Tridacnid is going to be on the substrate, I would suggest that you place a small piece of rock or tile about 1/8” to 1/2” below the substrate. When the clam starts to lay down its byssal filaments, it can attach to that object.  This will also prevent potential predators from entering the byssal opening and doing damage to vital organs.

Remember that acclimation takes time. When we transfer clams to a new aquarium, environmental factors may be significantly different from those to which the clams were previously accustomed. Thus, the clams must adjust to the new environment. That being said, it is best not to introduce more animals or change buffers (products) during this acclimation period. I firmly believe that the less additives that we put into our aquarium, the better the animals will be.  

   Closing Thoughts

Well, there you have it--a quick summary of the basics of selecting and placing Tridacnid clams in your aquarium.  I hope that this brief treatment has answered some of your questions regarding these remarkable animals.  I encourage you to educate yourself more with the many resources available in print and on the internet.  Never forget that your clam is an incredible living animal. Choosing your specimen carefully and providing for its well-being and health will bring you years of viewing pleasure.

You are welcome to check out my Clam Support Forum with any questions that you might have on the selection, placement, and care of Tridacnids at


WWM about Giant Clams, family Tridacnidae

Related Articles: Got Tridacna? A beginner's guide to keeping Tridacnid clams by Laurie Smith, Example Chapter from NMA Reef Invertebrates book, on Giant Clams, Tridacnids, Tridacnid Health: Pinched Mantle Syndrome in Giant Clams by Dr. David Basti, Deborah Bouchard & Barry Neigut, Bivalves, Mollusks, Lighting Marine Invertebrates

Related FAQs: Tridacnids 1, Tridacnids 3, Tridacnids 4, Tridacnid Clam Business, Tridacnid Selection, Tridacnid Compatibility, Tridacnid Systems, Tridacnid Lighting, Tridacnid Placement, Tridacnid Feeding, Tridacnid Disease, Tridacnid Reproduction, Lighting Marine Invertebrates,

Tridacna sp., N. Sulawesi.


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