Mollusk of the week: Tridacna Maxima, the Great Clam


Premium Member
Every week I will be posting a new mollusk for discussion. Please post everything you know about this week's mollusk, to include pics, care and feeding habits, optimal environment, common names, and anything else you can think of.

This week's mollusk is the Great Clam, Tridacna maxima.

The maxima clam, or great clam, is arguably the most popular of the Tridacnid clams. It can be found (or tank-raised) in a variety of colors from drab brown to the much-prized turquoise. Many or most of the maxima clams now being offered in the hobby are tank- or farm-raised, so keeping this creature in our tanks is becoming rapidly less detrimental to the wild reef.

Maxima clams love light, because they harbor photosynthetic algae (zooxanthellae) in the tissues or their siphonal mantle, the colorful portion of the clam that drapes over the shell when the clam is fully open. The zooxanthellae use sunlight and metabolic waste from the clam to manufacture food for the clam. The clam also filter feeds from the water column to some degree, taking in only the smallest of phytoplankton. Maxima clams attach to a hard substrate by way of the byssal gland, an evolutionarily modified "foot" that grasps the rock with threadlike appendages. The shell has scutes to lend it structural support.

To keep your maxima happy, place it on rock close to an intense light source, MH being preferable. Keep the water clean. Dosing phytoplankton is optional (some authors maintain that this is necessary for long-term health, and others disagree). Keep the tank free of creatures that would harrass the clam or try to eat it.

In aquarist's tanks, clam are occasionally parasitized by pyramid snails, tiny mollusks. Often a predator, usually a wrasse, must be introduced to prevent or end this parasitization.

Please post your information on, experiences with, and pics of your maxima clams.


Premium Member
Not the best photo, but it provide an example of the spectacular color of Maxima clams.


I think it's prudent to dose phytoplankton in a clam tank, and to have an appropriate wrasse, as mentioned in the initial post. Onw of the best attributes of the Maxima family of clam is the variety of mantle colors and patterns that can be found.


New member
Great pics Evets!

IMO, giant maxima clams love metal halide lighting. I feed cryopaste. Keep alk and Ca up and they should be one of the faster growing speciies in your tank.

Great colors. Look for ones that fully open their mantles. Some will have great color but do not open real wide. Parasite pyramidal snails will slow the growth of the clam and possibly kill it.

HTH, Scott

Sea Dragon

New member
Here's a purple one. It's more brilliant than it appears in the pic but the hue is about right.


This one is new so I'm just giving it the same care as my crocea: SG 1.026, temp 80F, 250 watts MH, dripped kalk, infrequent live phytoplankton. It's been with me a week and seems to be happy as a ar ar. :)


Premium Member
My t max has never attached to a rock. After researching this I found that it's not common but is nothing to worry about either. The first time I discovered this he had dropped deep into the rockwork and I had to tear half the tank apart to get him out. I've learned to place them somewhere that won't be fatal if they move. He recently moved off the second rock onto the substrate, after 8 months in the previous spot. He appears healthy and happy there so that's where he'll stay.

Although I have a calcium reactor and drip kalk I haven't seen the growth others report. Maybe a half inch in 12 months to a current 3". Lighting is 400w mh, other than fish food I don't add other foods, ca about 400, alk about 9dKH, pH 8.1 to 8.3, sg 1.025, and temp 80 to 81.



New member
Here are my two Maxima's


This Maxima is 2" and has camouflage pattern


This is my electric blue Maxima...3"

My tank is a 58 Oceanic with two 250w Ushio 10k HQI's and 285w VHO actinic. I keep all my clams on the sandbed. I have a dual chamber reactor that keeps my Alk at 11dkh, and Calcium at 480ppm. I keep my temp at 82 degrees, and sg at 1.025. I also dose every other day with a capful of DT's

[Edited by JG on 02-13-2001 at 02:52 PM]


Premium Member
Here is a pic of my T. Maxima:


You'll notice the color is not as vivid as the others, but has a outline of electric blue. It about 4 inches. Rest on a flat ledge about 10 inches below a 175W 10K MH. Had this guy for about 7 months. DT's are added to this tank.


Premium Member


Last call for information about T. maxima before this thread goes to the archive. If you have anything to share about this mollusk now is the time to do it. :D