Ryan invites John Bui from Clam Mania to answer our most pressing questions about caring for "Giant Clams" in a reef aquarium. Filmed LIVE at Reef-A-Palooza Dallas, we gather some valuable intel, debunk some myths, and even get a glimpse into the process of propagating these beautiful bivalves in captivity. Whether you're looking to grow a behemoth Tridacna gigas of your own or simply wondering what species of clam will thrive in your tank, you definitely don't want to miss this episode of 52SE!

"Giant Clams" is a common name that refers to any of the 12 described species belonging to the Tridacninae subfamily of bivalves. Although most clams in an aquarium are of the genus Tridacna, the term "Giant Clam" also includes the lesser-known genus Hippoppus.

Giant Clam Species

  • Tridacna crocea
  • Tridacna derasa
  • Tridacna elongatissima
  • Tridacna gigas
  • Tridacna maxima
  • Tridacna mbalavuana
  • Tridacna noae
  • Tridacna rosewateri
  • Tridacna squamosa
  • Tridacna squamosina
  • Hippopus hippopus
  • Hippopus porcellanus

1. Where are Giant Clams found naturally?

Giant clams are all found in coastal tropical marine environments from very shallow lagoons down to a maximum depth of about 65 ft. Each of the different species most often inhabits specific areas with the Tridacna Maxima being the widely distributed species around the world. When researching how to care for a clam, start by researching where the species is naturally found. This will help you provide the right environment in your tank - shallow clams often prefer higher light vs clams that are found deeper can tolerate much lower light levels.

2. Are small clams impossible to keep alive?

There is a long-standing belief that small clams (<2" long) are difficult to keep alive in an aquarium. As John Bui states in the video, this is simply a myth and the key to success with clams of any size is water chemistry and light. The explanation is often focused on the need to feed like phytoplankton to smaller clams because they are not able to collect enough light to sustain themselves. While clams do eat planktonic foods, they can survive just fine without heavy feeding as light is their primary source of energy, even small clams below 2" long. With stable chemistry and sufficient PAR, Giant Clams as small as 1" will thrive and grow in an aquarium.

Giant clams are the only photosynthetic clams in the world!

3. How much light do I need?

The best approach is to create an environment that suits the particular species. For all intents and purposes, 150 - 350 PAR is the general range that will keep most Tridacna clams happy. Clams can survive in 400+ PAR environments but it is important to slowly acclimate them over time or else they could bleach. Lower PAR levels below 100 might sustain a clam for some time but it will not thrive.  

Clam Mania Recommended PAR Levels for Giant Clams

  • derasa  - 150 - 350 PAR
  • crocea - 200 - 400 PAR
  • maxima - 150 - 350 PAR

4. How much flow does a clam need?

Clams can tolerate a variety of flow conditions but will thrive in medium to higher flow conditions. In captive propagation, strong gyre currents that reverse direction on a regular schedule with periods of rest in between is a common approach to flow.

5. Do clams need to be placed on the sand bed?

Place your clam in your tank based on PAR.  They will survive on the sand and they will survive on the rocks as long as the water chemistry and light are stable. 

6. Since clams are filter feeders, can they effectively filter my aquarium water?

Clams are filter-feeding bivalves and they will filter particulates from the water as they pump water over their gills. When it comes to an enclosed ecosystem like your aquarium that contains corals and fish, a single clam will generally not be a sufficient means of nutrient export.  Of course, this depends on your tank's bioload and how many clams you have; the more clams in your tank, the more filter feeding is done. Could you keep a tank with ONLY clams (no fish) without running a protein skimmer?  Sure, it is possible but not the reality for 99.9% of home aquarists.

7. What kind of parasites can threaten a clam?

Pyramid snails prey upon the flesh of giant clams and can enter your tank as a hitchhiker. Many species of wrasse will prey upon Pyramid snails and will make a great companion fish to any tank with clams. Leopard Wrasse, Coris Wrasse, and Melanarus Wrasse are common species kept alongside giant clams.

8. How fast do Giant Clams grow?

With ideal light and water chemistry, Gigas and derasa clams grow the fastest. Maxima and crocea are smaller and slower-growing species. Just like coral, the rate of growth is heavily influenced by the stability of the environment.

9. Will a Giant Clam change color over time?

Once a clam is about 1" in size, the visible colors will generally remain the same but can become much more vibrant over time as the clam grows larger.

10. How many clams can I put in my tank?

Like corals, you can put as many clams in your tank that will fit. As long as you maintain suitable light, flow, and water chemistry multiple clams will survive until there is no more physical room for them to grow. 

11. Are giant clams hardy?

Clams are most sensitive to light and water chemistry. It is critical to maintain stable alkalinity, and calcium with pH above 8.0. Lighting should be within the PAR range previously described. Beyond that, they can handle varying levels of phosphate and nitrate and likely acclimate to whatever conditions are in your tank.  Source a healthy clam, acclimate it properly, and maintain stable chemistry under the right light conditions and your odds of success are very high. 

12. What is burping?

There is no reason to physically burp a clam. If an air bubble gets trapped in the clam, they will expel it naturally as needed. 

13. What is "torn foot" and is it something to be concerned with?

Clams have a foot they use to move around which is like a muscle or suction cup that extends from the bottom side of the hinge area of the clamshell. They also develop byssus which is a bundle of filaments that form a permanent attachment to a rock or substrate. The foot is retractable while the byssus develops over time after the clam has established into an area where the conditions are ideal. Cutting the byssus will not harm the clam as it can grow new byssus again when it's put into another location. Byssus hanging from the bottom of the clam after being cut is NOT a torn foot. 

14. Is it possible to put a clam in a brand new reef tank - an "instant clam tank" so to speak?

It is possible to add clams to a brand new reef tank right away and the clams should survive so long as the stable environment is maintained.