Maxima Clam Care Guide: Tridacna maxima

Looking at a mature maxima clam in an aquarium, you can’t help but marvel at the size. No wonder people call them “great clams.” But they’re the THIRD largest of the giant clam species out there. (The average hobbyist doesn’t have the space for its cousins) The smooth giant clam (Tridacna derasa) and giant clam (Tridacna gigas) grow double and triple the size of the maxima. They also put on that size at a faster rate. We’re talking 4 inches (10.2cm) a year! In comparison, a healthy maxima only adds around 0.08-1.6 inches (0.2-4cm) each year. (Hence the name “SMALL giant clam”)

But when you’re looking for a stunning bivalve for your reef tank, you can’t ask for better. The mantle of the maxima clam comes in bright shades of blue, green, turquoise, and gold (and every shade in between). You’ll also find different patterns – with a few rare solid clams out there. You may even spot a variety with pigmented eyespots along the edge of the mantle. (Not a common find!) Under proper lighting, these mollusks stand out and draw a crowd.

Take a look at this YouTube video of Tahitian blue maxima clams (and try to resist the rich saturation of color):

The scutes (the scalloped edges) of the maxima are narrow. It’s one of the identifying characteristics of the species. You’ll also see a shell that’s longer than it is wide (at LEAST three times longer). And there’s no symmetry to that hinged monstrosity. Maxima clams are known for their asymmetry. If you look at the base, where the byssus gland resides, you’ll see a short hinge (the part of the shell responsible for opening and closing). In contrast, the opening for the byssus gland – where the byssal threads emerge – is relatively large.

That makes sense, considering the byssal threads (or byssal filaments) are how the clam anchors itself. The filaments bore into the substrate, creating a solid foundation for the shell. As the bivalve ages, those threads reach further and further into the rock. This prevents the maxima from getting tossed around in the surf. (And, yes, that’s going to become VERY important in a minute)

It’s common to come upon “colonies” of maxima clams throughout the Indo-Pacific. The mollusks show up in crystal clear waters that snorkelers prefer around Australia, India, Polynesia, and east Africa. And if you dive around the Red Sea, you’ll come across solid blue varieties. The warm, shallow water is the perfect environment for these mollusks.

All of the giant clam species grow at average rates. This makes aging an individual easy. Just measure the size of the shell from year to year. And all of the clams survive for a LONG time. For a maxima clam to reach that average size of 12-14 inches (30.5-35.6cm), it takes 50-60 YEARS. So taking on one of these beautiful mollusks is a long-term investment on your part.

Maxima clams are easy enough to find. Simply jump into the water anywhere around the Indo-Pacific. The bivalves make their home in shallow, CLEAR waters. If you can think of a tropical getaway, odds are you’ll find the colorful mantles tucked into rocky crevices along the reef. Maximas prefer areas with a strong current. They want the movement of the water to bring meals to them. (After all, they’re not going anywhere)

It’s a MUCH easier quest than Arthur undertook for the Holy Grail.

However, getting YOUR maxima clam settled in and comfortable is a quest in itself. While a sunny spot on the reef seems simple enough, duplicating the environment in your aquarium gets tricky.

And, as you might expect, cleanliness and tank health play a significant role in your maxima clam’s lifespan. They’re a sensitive species. You CAN’T allow ammonia, nitrite, or even nitrates to build up. This means adhering to a strict schedule of 25% water changes every week. Set up dosing to provide the trace elements the clam will need to survive if you can’t.

More than that, though, you need ALL of your water parameters to remain stable. Fluctuations in temperature, oxygen levels, pH, or alkalinity can make your maxima unhappy. And this is one time where you need to aim for OPTIMAL. All parameters come with a range. Usually, you can get away with “okay” or “acceptable.” That sometimes means falling at the bottom of the spectrum when you perform your testing. But that won’t work for these clams. It’s one of the problematic aspects of their care.

Maxima clams don’t care too much about your tank’s décor. However, they DO want rockwork. They need something solid to bore those byssal filaments into. And sand won’t do it. Live rock is porous enough to work, or you can choose another type of rock. Think of where you’d like your clam to sit in the tank FIRST. Because once it’s settled, you don’t want to cut those threads and move the mollusk. There’s too much risk of damaging tissue.

Making a pocket among the aquascaping works best. You don’t want the clam to fall. (Remember, it opens and closes the mantle, so it WILL shift) Don’t make any “tight fit” choices, either. If the mantle CAN’T open, the clam will starve. Find a Goldilocks solution. If there’s too much space around the rock the maxima is attached to, fill it in with sand. This will protect that byssal opening from pests. You can go halfway up the shell.

Maxima clams also need light – and a lot of it. They stick to the shallows to maximize the amount of sunlight they absorb. This fuels the photosynthesis carried out by the zooxanthellae within their mantle. (Yup, the same symbiotic algae you find in coral) Without proper light, the clam will starve. You need light bright enough to satisfy Acropora corals. (Yup, we’re talking that high)

But there’s a catch: the size of your maxima clam determines how much light they tolerate. Young clams (under 2 inches/5cm) have thin mantles. The intense light you’d provide a larger clam will “burn” the algae. So you need to keep them closer to the bottom. As they grow, you can move them higher in the tank to provide the proper lighting intensity.

How do you move a sessile mollusk? Easy – attach your maxima clam to a SMALL flat rock. Then you can move the anchor without disturbing your maxima too much. And once it acclimates to the light, settle it into that chosen spot. (Some clams come attached to this ideal bit of rockwork, making your life easier)

Maxima Clam Tank Size

When you get your first maxima clam of just 2 inches (5cm) in length, it doesn’t seem like you’d need much room. You want to keep their eventual size in the back of your mind, though. Yes, they grow slowly. But you don’t want to move them from tank to tank. That’s stressful, and you’re chances of losing the mollusk go up. Better to start with an appropriate aquarium in the first place.

Most clams won’t get any larger than 8 inches (20.3cm) in a home aquarium. So you CAN get away with 55 gallons (208L). However, the larger your tank, the easier it is to stay on top of your water quality. So your best bet is to go with a 100-gallon (379L) tank. Your maxima will have room to grow, and you won’t struggle to keep your water conditions under control.

You’ll also want to find a quality powerhead. In the wild, maxima clams settle in areas with a high current. This provides them with access to the richest particulates drifting in from the deeps. They’re filter feeders – sessile filter feeders; they don’t shift to find food. A powerhead mimics the water flow they rely on to gain additional nutrients. But it also keeps the clam CLEAN.

Tucked into a crevice, the maxima can get swamped with settling sand, uneaten food, and other debris. You can use a turkey baster to keep the area clean or employ that powerhead to wash over the clam. The “natural” motion of the water is the better option. It won’t startle the maxima, and it’s more effective. (No offense intended to your basting skills)

Are Maxima Clams Reef-Safe?

If you decide to try a maxima clam on sandy substrate, it WILL move itself. While not the most agile creatures, bivalves CAN use the muscles in the hinge to expel water from the mantle. Then they shift their position. (Scallops are the most mobile of the group) This allows them to find the best place on a reef to settle.

And while the image of a giant clam flopping around sounds horrible for corals, it’s not a big deal. Maxima clams don’t present a problem in reef tanks. (Yes, even if you put them on sand) As they open and close – or shift – the movement’s minor. And they don’t pose a threat to the corals around them.

If anything, you need to keep an eye on your CORALS. As some of the branching varieties stretch out, they can shade a maxima clam. Wedged in place, the clam loses the light it needs to feed its zooxanthellae. So you want to look where you’re placing those LPS and soft corals. If they’re becoming a nuisance, it may be time to do some fragging.

Maxima Clam Diet

Maxima clams receive meals from two sources: zooxanthellae and filter-feeding. In the mornings, they open the mantle to provide as much light as possible to the symbiotic algae. They also position themselves in high currents to obtain the best planktonic “snow.” When the sun sets? The mantle closes, and they “rest” for the night.

You’ll find plenty of debate among hobbyists on whether you need to feed your clam. Realistically, if you have proper lighting and a healthy current with live rock? You probably don’t need to worry about it. Your maxima will take care of itself. Well, provided your clam’s a mature specimen, anyway.

“Youngsters” under 2 inches (5cm) need some assistance. Their mantles – with attendant zooxanthellae – are still developing. So daily supplemental feedings in the form of greenwater or phytoplankton are in order. You don’t want to create unhealthy water conditions, though. And flushing food directly onto a maxima clam with a turkey baster will cause the mantle to close in defense.

So how do you feed a clam?

You can purchase a commercial clam feeder, of course. Or you can go the DIY route:

1. Cut the bottom from a soda bottle or milk carton. (Use a container slightly larger than the shell of your maxima)
2. Settle the bottle around the clam and hold it in place with one hand.
3. Squeeze the food through the “top” with your other hand.
4. Allow the food to drift down to the clam for several minutes. Then release the bottle.

This process works as the maxima clam grows. You just cut down the frequency of the feeding. Once the maxima’s 4 inches (10.2cm), drop down to 2-3 times a week. And at “adult” size? You CAN offer food once a week if you want. Just keep an eye on your water quality. You don’t want to end up with excess nutrients fouling things.

Hobbyists love maxima clams for their beauty. The array of colors and patterns – especially with the available commercial farming operations – mean endless opportunities for your reef tank. And while they’re not the most ACTIVE additions to an aquarium, you’ll still get to see the mantle open and close.

Maximas serve as hosts for plenty of crustaceans. The shrimp and crabs live in and around the shell, using it as a source of protection. In return, they remove tiny ectoparasites from the mantle. It makes for a dynamic reef display (provided you skip hermit crabs – they don’t play nice). Unfortunately, other invertebrates aren’t so pleasant. Pyramid snails are the bane of this clam’s existence. They burrow into and devour the soft tissue of the mantle. And getting rid of the pest can prove challenging for some hobbyists.

And the risk to the patterned mantle doesn’t stop there. Plenty of fish will pick at and nibble on clams. While the damage isn’t significant, the irritation can lead a maxima clam to remain closed. If a clam doesn’t open, it can’t receive light. And that means death via starvation. To prevent this unwanted outcome, avoid any of these “pickers:”

• Angelfish
• Blennies
• Butterflyfish
• Gobies
• Puffers
• Tangs
• Triggerfish

Breeding the Maxima Clam

Maxima clams exhibit protandry hermaphrodism. They hatch male, developing female traits later on in life. Captive propagation is easy, which is why most clams are aquacultured these days. Of course, when ONE clam can produce eggs in the THOUSAND range, you’re looking at a problem with tank “pollution.” This is why most hobbyists leave clam reproduction to the experts.

In the wild, maxima clams spawn around sunset. Sperm are released first, with eggs released later. This prevents a maxima from self-fertilizing (a bad idea from a genetics perspective). The gametes fuse and form an egg. Within 12 hours, the egg hatches into a free-swimming trochophore. The trochophore remains part of the plankton, then metamorphoses into a veliger.

Veligers are still free-swimming, but they look like clams. And this stage allows them to start filter-feeding. They swim to the shallow reefs maxima clams prefer and find an ideal spot to settle. They’ll then develop their foot, which allows them to hold on to the substrate.

Another 8-10 days and they metamorphose into a juvenile clam. Once they’re a juvenile, they get their zooxanthellae. And within 2-3 years, they’ll develop female reproductive organs, allowing them to start the cycle again.

That’s A LOT of work and care for your average hobbyist. And you need to know which stimulus – temperature, salinity, etc. – to adjust to trigger spawning. Since maxima clams are so sensitive, it’s best left in the hands of aquaculture facilities.

As soon as you see a maxima clam in all its glory, you’ll want one. The colors, alone, complete ANY reef tank. And how many people can claim they own a giant clam? But these mollusks aren’t the easiest to manage. So before you rush to choose a particular color (or pattern), take the time to review the pros and cons. It could save you some grief in the long run.

Pros

• Most maxima clams come from aquaculture, preventing the need for wild collection and the stress of removal or transport.
• You don’t need to offer supplemental feeding to a mature maxima, provided you have proper lighting and water flow.
• Maxima clams provide shelter for shrimp and crab species.

Cons

• Maxima clams are sensitive to ANY changes in your water parameters; you’ll need your tank to remain as stable as possible.
• You need a mature tank, stable for at least six months before you can introduce even a young clam.
• Maxima clams are susceptible to predation by pyramid snails and often get nipped at by fish and crustaceans.

If you’re willing to roll up your sleeves and invest in the time and effort to maintain a controlled environment, the joys of maxima clam ownership COULD be yours. Will the work be worth it? How can you say no as you watch that blue, purple, or gold mantle open in the morning? These bivalves promise endless delight. But if you need some extra convincing, we’ve got you covered.

This YouTube video walks you through everything you need to know about maxima clams:

Want to know about some of the best maxima clam tank mates?

If you find yourself confronted with an infestation of pyramid snails, these natural pest control methods will help:

Conclusions

No two maxima clams look alike. It’s one of the best things about this invertebrate. Well, and the fact that once you’ve created the perfect home, they’ll happily stay in place. (Not too many other reef creatures can say that!) But these clams aren’t the easiest. You’ll need to put in the effort to keep them healthy.

It’ll be worth it, though. Especially when you brag you’ve got the Holy Grail stashed away at home.

References