Maxima Clam - Tridacna maxima

Great Clam ~ Rugose Clam ~ Maxima ~ Small Giant Clam

Tridacna Maxima, known as Maxima Clam, Great Clam, Rugose ClamTridacna maximaPhoto: Keith Berkelhamer

   One of the favorite giant clams is the beautiful Tridacna maxima, the Maxima Clam!

   The Maxima Clam, Tridacna maxima, is one of the most beautiful of the Tridacna clams. Maxima Clams usually show a variety of rich colors and patterns. These gorgeous colorings of its mantle arguably make it one of the most popular of the Tridacna clams. Vying for this honor is its close cousin, the Crocea Clam Tridacna Crocea. Though a bit smaller than the Maxima Clam the Crocea Clam is another highly colored, beautiful, and favored giant clam.

   Colors of the Maxima include combinations of blue, brown, green, gray, purple and yellow. Patterns can be stripes, blotches, or spots. More so than in other Tridacna clams, there are usually larger areas of a solid color in the Maxima. Solid blue Maxima Clams have been found in the Red Sea. A markling often seen on he Maxima Clam is a prominent row of black pigmented eye spots along the edge of the mantle. But though these markings are common, they shouldn't always be expected.

   Being one of the most readily recognized of the giant clams in the aquarium industry, the Maxima has been dubbed by some enthusiasts as the "Holy Grail of Reef Aquariums". Besides Maxima Clam, other names the Maxima is known by are the Great Clam, Rugose Clam and Small Giant Clam. With some specimens being intensely colored and strongly patterned, you will also find references to them in the aquarium industry under a variety of descriptive names such names as Ultra Maxima Clam, Wild Ultra Blue Maxima, Blue Maxima, Golden Maxima, Teardrop Maxima, and Zebra Maxima.

Geographic Distribution
Tridacna maxima
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Scientific name

   Tridacna maxima


   The Tridacna maxima is listed on the IUCN Red List as LR/cd - Lower Risk/conservation dependent.


   The length of a mature Maxima Clam can reach between 14 to 16 inches (35 - 40 cm) though their average length is usually smaller, about 12" (30 cm). The shell of the Tridacna maxima can vary depending on the environment they are in and the crowding of corals and other clams nearby. Some characteristics of Tridacna maxima's shells are:

  • usually asymmetrical and elongated
  • three times longer than they are broad
  • they have a short hinge
  • they have a large byssus gland opening
  • scutes are usually low and close together
  • the lateral distance between scutes in adjacent rows is usually less than the scutes' width

  The inhalant siphon on the Maxima has small, fine tentacles. The mantle will sometimes exhibits an undulating shape with tubercles that are light sensitive. Although it is rare, the tubercles are sometimes quite numerous.

Purple Tridacna maxima

Comparing Maxima Clams to other species of Giant Clams:

   Maxima Clams are often confused with the Crocea Clam T. crocia. This is because the color patterns of these two clams is similar. Their differences can be determined by their shells and their byssus glands.

   The shells of the Maxima Clam and the Crocea Clam are much different. The Maxima Clams usually have an elongated shell. The scutes of T. maxima are also more pronounced and they cover most of the shell.

   Their difference may also be determined by the byssus gland.

  • On the Crocea Clam the byssus gland is very long and wide while the Maxima Clam's have a smaller byssus opening.
  • Also the byssus opening on the Maxima extends towards the edge of the shell, but not as much as on the Crocea.
  • The byssus opening's edge on the Maxima's tend to curl upwards with a chitonous ring surrounding it.

   Compared to the Squamosa Clam Tridacna squamosa, the shell of the Maxima Clam is asymmetrical. Young Squamosa Clams are sometimes confused with the Maxima mostly because both clams have scutes on their shells. The rows of scutes of a Maxima Clam are smaller and closer together than those on the Squamosa, and the hinge on the Maxima is smaller.

Difficulty of Care

   The Maxima Clam is not only beautiful, but can be a good choice for a beginning saltwater enthusiast. Both the Maxima Clam and the Crocea Clam are fairly tolerant of strong water motion and relatively strong fluctuations in water parameters, more so than some of the other Tridacna clams.

Foods / Feeding

   It is generally believed that giant clams do not require feeding in the aquarium. Most clams fulfill their nutritional requirements by filter feeding and absorbing dissolved organic compounds from the water. The Tridacna clams have gone even further than this, using zooxanthellae to manufacture food for themselves.
  The Tridacna clams receive the majority of their nutrition from their zooxanthellae. Whether additional feeding is required is still debated. Some enthusiasts believe they should be fed, going on the assumption that they are filter feeders like other clams. If you wish to feed your clam, it is suggested that they be fed micro-foods designed for filter feeders, especially when small. A yeast-based suspension is one suggestion, unless the tank has other fish and corals that are regularly being fed, or you can offer other micro-foods such as phytoplankton or commercially prepared micro-foods like 'marine snow' or 'reef snow'.
  Basic nutrients in the aquarium that giant clams need are calcium, strontium, iodine, and possibly a minute amount of nitrate.

  • Calcium: Calcium is the main building block for clams and should be present in the water at levels of at least 280 mg/L for growth to occur. More rapid, natural growth is seen when calcium is in the range of 400-480 mg/L.
  • Strontium: Strontium is incorporated in the shell along with calcium and should also be provided for optimum growth.
  • Iodine: The addition of iodine to the aquarium will also enhance growth and color in giant clams.
  • Nitrate: They require some nitrogen for proper growth. Nitrate can be added if levels are extremely low, but be careful as nitrates should never exceed 2 mg/L.

   For more information about the feeding process of Crocea Clams see What Do Clams Eat.

Aquarium Care

   If a healthy clam is obtained and proper light provided, these clams are relatively easy to keep. With proper lighting and careful attention, Maxima Clams require require little else in the way of care. It is important to make sure they are not being irritated, not being fed upon by other organisms, and good water quality must be maintained.

  • If you have a healthy specimen, it will attach itself to the substrate in less than a day. Keep this in mind when placing your clam in the tank. Make sure you put it where you want it to stay.
  • Keep a watch for predators as this clam can be easy prey with its large and wide byssus gland opening.
  • Maxima Clams can handle strong water motion and relatively strong fluctuations in water parameters, but you really don't want your water parameters to fluctuate too much!

Aquarium Parameters

   Maxima Clams can be kept in a reef environment with live rock. Placing a Maxima Clam in your tank is pretty much the same as placing a Crocea Clam. They should be placed on live rock or some other solid material they can attach to. They can handle strong water motion and relatively strong fluctuations in water parameters, but high pH and high temperatures can cause problems.

  • Lighting:  Coming from shallow waters in the wild, these clams will need intense lighting. Pay attention to the color of the clam's mantle and use that as your judge for where your clam should go. Some T. maxima's will show vivid coloration and others will be showing off the brown color of their zooxanthellae. If your clam's color is iridescent, it has adapted to bright lighting and should be placed closer to the top of your tank. If your clam is mainly brown, it should be placed lower in your tank away from strong lighting.
  • Temperature: Upper 70° F. (mid 20° C.). Do not let the aquarium exceed 82° F.
  • Salinity / Specific Gravity: 1.024. Salinity is also important, too high or low a salinity can cause the death of a clam. Try to keep specific gravity between 1.023 and 1.025.
  • pH: 8.3. Do not let the aquarium exceed a pH above 8.4.
  • Hardness: Maintain a dkh of 7.9.
  • Water Movement: Maxima Clams can handle strong water motion, however high currents should not be a constant condition.

For more in depth information on caring for Maxima Clams see, Caring For Tridacnid Clams

Compatibility and Social Behaviors:

   Clams are very stationary and peaceful, they are not aggressive towards other aquarium inhabitants. Though they have the ability to shut completely, they do need protection from anemones and some corals. They should not be kept near any stinging cell creatures and must be kept away from any sweeper tentacles. Anemones need to be watched, as they can move close to a clam and sting or eat it.
   Be cautious with other tank inhabitants as well, those that may pick at the clam or eat its mantle, such as Trigger Fish and Puffers. Blennies, Butterfly Fish, Clown Gobies, Angelfish and shrimp may disturb Tridacna clams.

Breeding and Reproduction

   Maxima Clams have been propagated in captivity, and the demand from aquarists has raised interest in producing colorful varieties of all the tridacna clam species.

   For detailed information of tridacnid propogation, see Giant Clam Breeding and Reproduction

Potential Problems

   Keep a watch out for predators! The Maxima Clam can be easy prey with it's byssus gland opening. They are also quite sensitive to chemicals or toxic substances dissolved in the water, so be sure to maintain good water quality. As mentioned under aquarium care and aquarium parameters above, high pH, high salinity, and high temperatures can also cause problems.

  For in depth information on potential Tridacna clam problems, see: Tridacnid Clams: Friends, Enemies & Ailments


   Clams obtained from aquaculture systems are readily available and are very hardy in reef aquariums.

  According to The Reef Aquarium, Maxima Clams are relatively hardy but they can be delicate, and many of the clams found in your local fish stores are still wild caught (March 2000), but aquacultured clams are becoming readily available.

Authors: Elizabeth M. Lukan / Clarice Brough, CFS.
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