Tridacnas

Tridacna Clams are common inhabitants of Indo-Pacific Coral Reef benthic  communities in shallower waters.

Tridacna Clams have become very popular among marine aquarists.

The most distinguishing feature of Clams is their large two-part shell and interior mantle.

Most have intricately colored patterns in the mantle, making them attractive additions to the marine Aquarium.

By day, the Clams spread out their mantle so that the algae receive the sunlight they need to Photosynthesize, whereas the color pigments protect the Clam against excessive light and UF radiation.

The Clam should be placed on a horizontal surface that exposes the entire mantle to light because Clams rely heavily on Photosynthesis.

Using some rubble rock to prop the Clam up helps prevent the Clam from falling over until it attaches. When disturbed, the Clam closes its shell. 

Keep Clams away from other aggressive Corals.

Also be sure your Tank does not house any Clam predators.

Certain Wrasses and Angelfish have been known to attack and devour Clams in an Aquarium.

Remember to give your Clam plenty of room to grow. Mature Tridacnids can grow quite large.  

Larger clams, 3” or larger, are hardier and easier to acclimate into your home Aquarium.

Although Clams seem like a simple animal, they have complex organs. Each have gills, a stomach, a heart, kidneys, gonads, siphons, mantles, byssus gland, byssal threads, hyaline organs, eyes, and more.

Diet / Nutrition

Tridacna Clams are filter feeders and constantly filter the water for small particulates. Tridacna Clams larger than 2" do not require Supplemental feedings, but smaller Tridacna that are less than 2" should be fed a Phytoplankton or greenwater Supplement several times per week if maintained in a Nutrient poor Reef Aquarium.

Many aquarists don’t feed their Clams at all as the tanks waste and the Clams Zooxanthellae are plenty to keep it happy.

Adult Clams can get most (70–100%) of their Nutrients from the algae and the rest from filter feeding.

Clams filter tons and tons of water daily, so they will act as a Nutrient sink in even the most overcrowded tank.

Lighting Requirement

In the home Aquarium, Tridacna Clams require moderate to high lighting to thrive as they contain the symbiotic algae called Zooxanthellae, and receive the majority of their Nutrition from the light through Photosynthesis.

Smaller Tridacna that are 2" or less in size are much more sensitive to very intense lighting as their membrane is much thinner than larger specimens. For this reason, care should be taken to properly photo-adapt them to the existing Reef Aquarium lighting in a similar manner to newly introduced stony and Soft Corals.

When adapting a new Tridacna Clam to very intense lighting, it is ideal to set them on a small rock or in a plastic dish with coarse substrate at the bottom of the Aquarium. Over time, the Clam can then be slowly moved up higher in the Aquarium.

Unless you are feeding older Clams multiple times a week, most recommend a PAR rating of 250+ is typically recommended, and scientific experiments have shown they are much more productive at PARs of 700-1200.

Water Parameters

Clams need a Tank with stable Water Parameters 

• Salinity : SG 1.023-1.026
• Alkalinity : 7-12 dKH.
• Calcium : 380-450 PPM
• Magnesium : 1280-1350 pH : 8.1-8.4
• Phosphates: 0,05 -0,3
• Nitrates : 2-20
• Strontium : 6-10 PPM
• Iodine : 0.04-0.08 PPM

If any of these Parameters falls out of place, the Clam will suffer and likely die.

Nitrates are usually a problem for SPS keepers, who tend to keep them close to zero.

But, Clams require Nitrates of at least 2 ppm, or they will starve.

Calcium and Alkalinity, and the other elements to a lesser degree, are used very quickly by Clams and must be tested regularly to ensure you or your doser is dosing enough back into the system to keep up with the Clams demand and usage.

Water Flow

Water movement is crucial.

Because they come from shallow Reefs, Clams are used to strong current and waves.

But, most home Aquariums rely on plain linear flow.

While Clams do not prefer this, they can adapt to live with it as long as you set it up correctly.

You need to ensure that the water flow doesn’t cause your Clams mantle to fold upwards much, and that the Clam doesn’t retract its mantle too much.

If these things occur, your Clam will ultimately die.

Be sure his mantle is fully extended during the day, and appears to be full, happy, and actively pumping water through its siphons.

Pests / Diseases

The biggest concern for Clam owners is the dreaded Pyramid Snail.

These tiny snails,  no bigger than ¼ inch,  look like a grain of rice.

Pyramidellids normally occur close to the mantle edge on the shell of the host, where they penetrate the soft tissues using a stylet and proboscis and feed off the Clam tissue fluids.

They will attack and consume the mantle or flesh of the Clam.  

They reproduce very quickly and can be really difficult to remove.

Be sure to check under the Clam by the foot and all around the shell for the snails and their egg sacs.  

In larger Clams you may find Symbiotic Shrimp or small ‘Pea Crabs’ living inside the Clam. These are fine to keep and are incredibly difficult to remove without damaging the Clam.

The shell of the Clam can also hold a variety of other parasites and hitchhikers such as Aiptasia Anemones, bristle worms, and nudibranchs.

If you do find any hitchhikers you will want to physically remove them before placing the Clam into your tank. A tooth brush and a pair of tweezers works really well. Be sure to clean the Clam thoroughly in a separate container.

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

If your Tridacna is weakened, you can do therapeutic baths.

The doses are: 1 teaspoon of glucose for every 2 liters of water.

spend 1 hour baths every other day 4 times with periodic inspection to eliminate surviving snails.

This cure revivified the animals, and they began to open completely durng the first bath.

Telling Clams apart

When placing a Tridacna Clam in your Tank it is important to know the exact species of Clam you have.

The four most readily available species of Tridacna Clams are Crocea, Maxima, Derasa and Squamosa.

Crocea and Maxima Clams are found in rocky habitats, so they should be placed in the rock work or on hard substrate. 

They have byssal glands (foot) that will need to attach to a solid surface.

Derasa, Squamosa Clams are best placed on sandy substrate and typically need less intense lighting.

Crocea Clam

These Clams are also referred to as Crocea Clam, Boring Clam or Crocus Clam, and are the smallest of all Tridacna spp., reaching a maximum size of 6" in the wild.

In the wild, the Crocea Clams often live together in great congregations, and can display a variety of colorations and patterns comprised mostly of purple, green, brown, and blue with lighter colored spots and markings.

Vibrant blue or green Crocea Clams as well as ones consisting primarily of gold normally demand a higher price and are considered Electric, Ultra Colored, or Premium Colored.

They can be identified by having a relatively smooth shell that is thick and heavy, and is much taller than Maxima, which it can closely resemble in the appearance of the mantle.

Like some other members of its genus,  Crocea attach to hard substrate or rockwork with thread like appendages called byssal filaments, and can eventually burrow or bore into porous substrate or rockwork in the home aquarium.

Crocea Clams will arrive either unattached or attached to a small piece of rock or substrate.

They will normally attach to a solid surface within a few days of being introduced into the Aquarium, so keep in mind that their first placement should be considered permanent.

Never forcibly remove an attached Clam from the substrate or rockwork, as lethal damage to their foot and other tissue will be inevitable.

As a last resort, to remove a Clam from a hard surface gently cut each byssal thread with a razor blade as close to the attachment point of the rock or solid surface, making sure not to slice or damage any tissue.

Maxima Clam

The Maxima Clam is also known as the Small Giant Clam and is one of the most widely recognized species of the Giant Clams.

Maxima Clams are found in an endless variety of colors and patterns, and these Clams are graded for size, their intensity of coloration, and how complex their patterns are, and then priced accordingly.

Larger Clams that have the most intense coloration and intricate patterns are much more expensive.

Maxima Clams can be identified by having a more elongated shell that lacks symmetry, with narrowly spaced scutes or scallops on the upper portions of each side of their hinged shells.

Like some other members of its genus, Maxima attach to hard substrate or rockwork with thread like appendages called byssal filaments, and can eventually burrow or bore into porous substrate over time. 

Maxima clams will arrive either unattached or attached to a small piece of rock or substrate.

They will normally attach to a solid surface within a day or so of being introduced into the Aquarium, so keep in mind that their first placement should be considered permanent.

Never forcibly remove an attached clam from the substrate or rockwork, as lethal damage to their foot and other tissue will be inevitable.

As a last resort, to remove a Clam from a hard surface gently cut each byssal thread with a razor blade as close to the attachment point of the rock or solid surface, making sure not to slice or damage any tissue.

Derasa Clam

Tridacna Derasa is also referred to as the Southern Giant Clam or Smooth Giant Clam, and is the second largest of all the Tridacna spp., reaching a size of 24" in the wild.

Unlike most other Tridacna spp. that have a large byssal opening, Derasa Clams have a narrow gap on the underside of their thick, smooth shell.

They can easily be confused with their close relative Tridacna Gigas, especially when they are very small in size.

Derasa can be identified by having six to seven vertical folds in their shell which they can close completely, where Gigas has only four or five vertical folds, and is unable to completely close their hinged shell.

Although they can be found in a variety of colorations and patterns in the wild, the ones aquacultured for the Aquarium trade are primarily gold, brown, orange, and yellow, with vibrant blue or green trim edging that surrounds the mantle.

Derasa will arrive unattached to any rock or substrate, and prefer to be placed in the sand or in a recess of a rock, as they do not attach as firmly to the substrate or rockwork like most other members of the genus.

Squamosa Clam

The Squamosa Clam is also referred to as the Scaled Clam, as its species name Squamosa is the Latin word for scale.

The numerous rows of large scales over its entire shell are often used as shelter by other organisms, such as small crabs, bivalves, and other sessile invertebrates.

The shell is symmetrical, and the matching growth pattern of its shell allows it to close together very tightly to protect itself from predation.

The Squamosa Clam has a wide byssal opening and long tentacles surrounding its incurrent siphon, and attaches weakly to solid substrate with byssal filaments.

All of these Clams entering the Aquarium trade are cultured in the Central Pacific and South Pacific Ocean, and are primarily gold, brown, and yellow in coloration, occasionally having orange, green, or blue spots.

The rarest color form of Tridacna Squamosa is all blue, and this color form is rarely available in the aquarium trade, demanding a very hefty price.

Squamosa Clams will arrive either unattached or attached to small pieces of substrate. They will normally attach to a solid surface within a week or so of being introduced into the Aquarium.

Once attached to a solid surface, never forcibly remove an attached Clam from the substrate or rockwork, as lethal damage to their foot and other tissue will be inevitable. As a last resort, to remove a Clam from a hard surface gently cut each byssal thread with a razor blade as close to the attachment point of the rock or solid surface, making sure not to slice or damage any tissue.