Crocea Clam: Tridacna crocea
Crocus Clam, Boring Clam, Saffron Colored Giant ClamFamily: Cardiidae Tridacna croceaPhoto © Animal-World: Courtesy David Brough
The "dwarf" of the giant clams, the Crocea Clam is spectacular, stunning and spatially friendly!
The Crocea Clams Tridacna crocea are some of the most colorful members of the giant clam family. They are found in a variety of patterns and color mixtures. The mantle is usually decorated with blotches, spots, or lines. They have fascinating designs of iridescent blues and purples, yellows and greens, browns, gold, and oranges.
These beautiful clams are often simply referred to as 'Crocea', but the Crocea Clams are also known by a number of common names including Crocus Clam and the Saffron Colored Giant clam. Some specimens are so intensely colored and strongly patterned, that you will also find references to them in the aquarium industry under such names as Ultra Crocea, Ultra Grade Crocea, Super Crocea, and Electric Blue Crocea.
The Crocea is a boring clam, burrowing into boulders and coral heads in the wild. So it is also called the Boring Giant Clam. However, they lose the need to bore into rock if they are captive grown. This is also the smallest of the Tridacna clams, with its maximum length being only 6 inches (15 cm), making it a great addition to a reef tank.
The Crocea Clam is a favorite. Being the most colorful of the Tridacna genus, it could arguably be said to be the most popular, vying only with the Maxima Clam for the honor. Saltwater aquariums fascinate us because of the unique personalities and antics of their inhabitants, so perhaps a giant clam just sitting there seems a rather unlikely choice. But after one look at these beautiful creatures it is easy to understand why enthusiasts are eager to include them in their tanks.
For more about keeping Tridacna Clams, see:
Giant Clam Care: Caring For Tridacnid Clams
Crocea Clam, Tridacna crocea, Spawning
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Spawning in a captive environment
The Crocea Clam reaches sexual maturity around 3" and/or 4 to 5 years. They will shoot out their sperm or eggs every 2 minutes. A good skimmer to help rebalance the water parameters will help if one of these events occurs. SPS tanks with about 2 ppm of nitrates is the perfect environment for your clam.
- Minimum Tank Size: 50 gal (189 L)
- Aquarist Experience Level: Intermediate
- Temperament: Peaceful
- Temperature: 74.0 to 83.0° F (23.3 to 28.3° C)
- Size of organism - inches: 5.9 inches (15.01 cm)
- Diet Type: Omnivore
- Suitable for Nano Tank: No
The Crocea Clam Tridacna crocea was described by Lamarck in 1819. They are found in the Indo-West Pacific from the Andaman Islands to Fiji and then North to Japan and southward to New Caledonia and Queensland. This species is listed on the IUCN Red List as least concerned. Though often simply referred to as a 'Crocea', other common names include Crocus Clam, Saffron Colored Giant Clam, Boring Clam, and Boring Giant Clam. In the aquarium industry they will also be found under such names as Ultra Crocea, Ultra Grade Crocea, Super Crocea, and Electric Blue Crocea.
Crocea Clams are usually found in the shallow areas near the shore or on the upper-most areas of the reef. They have been found at depths of 1 to 66 feet (0 to 20 meters), however they tend to be more numerous at shallower depths. These clams are known as the Boring Giant Clam because with the contraction and relaxation of their byssal muscles, they burrow into boulders and coral heads. Once burrowed, they use their byssal threads to hold themselves in place. Usually only the top edges of the shell and mantle are visible. They lose their desire to burrow, however, when raised in captivity.
Giant clams are filter feeders. They take advantage of the phytoplankton, microscopic organisms that inhabit the sunny upper waters such as dissolved organic matter like ammonium nitrate. However, their largest source of food comes from the sun and the zooxanthellae found in their mantle. Predators are small pyramidellid snails that bore into their tissue and feed on their bodily fluids. While this is less of a problem in the wild, it is more of an issue in enclosed systems.
- Scientific Name: Tridacna crocea
- IUCN Red List: LC - Least Concern
Crocea Clams are the smallest of the giant clams, which makes them great reef tank inhabitants. They are slow growing too, expanding at only a few millimeters per month.
They grow up to 6 inches (15 cm) and are mature around 4 or 5 years. The females are sexually mature at about 3 inches (7.5 cm) and the males mature when they are slightly larger than that. Many aquarists have kept Tridacna Crocea clams for 15 to 20 years, however this genus has been known to live over 200 years in the ocean.
Photo © Animal-World
Crocea Clams have a soft, laterally compressed body that is enclosed in an elongated shell. The shell consists of two hinged parts, with the hinge being less than 1/2 to 1/3 the length of the shell.
The hinge has an opening, called the "byssal opening," where a muscular foot attaches to a hard surface. This muscular foot slowly burrows into the reef at the place where the clam settled during its larval stage, making it relatively safe from predation.
The picture to the right clearly shows the scutes on the upper portion of the shell only. The lower scutes have been worn away by the clam's burrowing habits.
They have no head, but their soft body consists of a mantle forming an outer wall that encloses a visceral mass containing the body's organs. The mantle protrudes in the form of flaps that are usually quite colorful.
The siphon, also called the intake siphon, is a fleshy tube-like structure that is part of the mantle.
Photo by Harbor Aquatics
The intake siphon is used to direct water flow into the mantle cavity and across the gills. The image to the right clearly shows the tentacles on the inhalant siphon of the T. crocea.
The fleshy mantle of the Crocea Clam is usually blue, yet it can be a combination of rainbow colors as well as brown and gold. It will usually have iridescent blue, green or yellow lines or blotches on top of the main color.
The shell can be grayish-white and at times will be tinted with orange, yellow or a pinkish-orange. Those colors will form a band at the upper margin of the shell along the inner surface.
Some characteristics of Tridacna crocea:
- there is a large and wide byssus gland opening
- the inhalant siphon has very small and fine tentacles
- shell has a symmetrical shape
- smooth shell with closely placed scutes
- scutes are on the upper portion of the shell only
- clams from aquaculture systems will have scutes along the entire shell since they haven't ground them down as a result of burrowing
When giant clams are juveniles, it can oftentimes be difficult to tell them apart. The Crocea Clam is sometimes confused with both the Maxima Clam T. maxima and the Giant Clam or Gigas Clam T. gigas.
Comparing Crocea Clams to other species of Giant Clams:
- Maxima Clam:
Crocea Clams are often confused with the Maxima Clam T. maxima because the color patterns of these two clams is similar. The Maxima Clams usually have a more elongated shell, and the scutes are more pronounced and cover most of the shell. Their difference may also be determined by the byssus gland, which on the Crocea Clam is very long and wide.
- Giant Clam:
When Giant Clams T. gigas are young, they are also sometimes confused with the Crocea Clam. The differences are in the coloring of each clam and the shell. The shell of the T. gigas is generally missing scutes (or they are very sparse) and the shell's ribs are more pronounced.
- Size of organism - inches: 5.9 inches (15.01 cm) - Sexually mature at 3" (7.5 cm), around 4 to 5 years of age.
- Lifespan: 200 years - They can live over 200 years in the wild. They are reported to have a lifespan of 15- 20 years in captivity.
The Crocea Clam is the smallest of the “Giant Clam” family, only growing to 5” or 6” in captivity, which makes them great reef tank inhabitants. This species is beautiful, but difficult to care for, so it is not suggested for a beginningaquarist. Both the Crocea Clam and the Maxima Clam are fairly tolerant of strong water motion and relatively strong fluctuations in water parameters, more so than some of the other Tridacna clams. However most have a poor record for long term survival so they are recommended for the intermediate to advanced aquarists.
When obtaining a captive grown clam, getting a specimen that is at least 2 inches, ideally 4 inches, is best. Smaller specimens do not ship well nor do they adapt as easily. If obtaining a clam from the wild, you will have a much better chance of success if you receive it still attached to a rock.
When a healthy Crocea Clam is obtained, with carefully handling and proper lighting it will establish itself. When first obtained, inspect the clam's shell for predators. It is important to make sure they are not being irritated or fed upon by other organisms. They are sensitive to being handled, so avoid that as much as possible.
A clam that is predominately brown and showing little of its normal coloration and patterning, should be placed lower in the tank away from strong lighting. The brown coloration is the clam's zooxanthellae showing and is probably due to the clam losing its protective coloration during shipping. While they will adjust to their new surroundings in time and become a little more hardy, but avoid wide fluctuations in light, water flow, reef water parameters (calcium, magnesium, etc.), and salinity.
If they are positioned where the water flow causes them to fold their mantle upward or close, this will cause the clam to eventually starve and die. Their coloring is incredible but they are also one of the most demanding clams when it comes to lighting. Once they adjust to the lighting, which is suggested at 400W metal halide or a high intensity LED, the light must stay constant. The mantle will extend excessively if the light is not strong enough. If you need to move them, take a few weeks to slowly get them into their new position or they will go into shock.
- Aquarium Hardiness: Moderately Difficult
- Aquarist Experience Level: Intermediate - Suggested for an Intermediate to advanced aquarist.
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. They receive the majority of their nutrition from their zooxanthellae. Yet research has shown that all Giant Clams that are under 4" do not have enough mantle tissue to provide enough space for zooxanthellae to keep the clam alive. Clams under 2" to 4" need regular feedings of phytoplankton.
It is generally believed that mature giant clams do not require feeding in the aquarium. Whether additional feeding is required is still debated. Some hobbyists believe they should be fed, going on the assumption that they are filter feeders like other clams. Basic nutrients in the aquarium that giant clams need are calcium, strontium, iodine, and a minute amount of nitrate that is at least 2 ppm. They will not thrive at a level of 0 nitrates.
Four ways clams make food for themselves:
- These clams have large amounts of zooxanthellae that live in their tissues. With plenty of light this algae will make too much food for themselves and the extra carbon and glucose is given to the clam (similar to most reef corals).
- The actual zooxanthellae themselves can be eaten by amoeboid cells within the host clam if needed.
- Giant clams have the ability to absorb nutrients like ammonia, nitrate and phosphates from the water.
- Giant clams are filter-feeders, straining fine particulates like phytoplankton, zooplankton and detritus from surrounding waters with their specialized gills.
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 that has been mechanically whisked, live phytoplankton or commercially prepared micro-foods like 'marine snow' or 'reef snow' can be offered. This may not be as necessary if there is a healthy population of fish in the tank.
With plenty of fish present, direct feeding is not as critical once they are over 4" long. When there is a good fish population, most clams fulfill their nutritional requirements by filter feeding and absorbing dissolved organic compounds from the water. Larger clams, however, may still benefit from phytoplankton foods fed on a regular schedule in an aggressively skimmed tank. For more information about the feeding process of Crocea Clams see What Do Clams Eat.
- Diet Type: Omnivore - Nutrition is obtained through filter-feeding of phytoplankton, zooplankton and detritus along with lighting and the marine algae, zooxanthellae.
- Flake Food: No - Will not eat this food
- Tablet / Pellet: No - Will not eat this food
- Live foods (fishes, shrimps, worms): Half of Diet - Clams under 4" will need live phytoplankton to thrive.
- Liquid Foods: Half of Diet - Marine snow or other phytoplankton substitutes, especially if there are no fish. Lighting makes up the rest of the food.
- Meaty Food: Some of Diet - Most comes from lighting.
- Feeding Frequency: Daily - Daily for clams up to 2" and several times per week for clams up to 4" is recommended. Can be fed weekly when full grown, but do not feed if there are plenty of fish in the tank.
Photo by Harbor Aquatics
Good water quality must be maintained, but if a healthy clam is obtained and proper light provided, these clams are relatively easy to keep. With careful attention paid to water parameters and proper lighting, Crocea Clams require require little else in the way of care.
Stable tank conditions are required to keep the Crocea Clams healthy. Do typical water changes of 20% a month, 10% biweekly, or 5% weekly. It has been noted that 5% weekly water changes replenish many of the needed additives.
Basic nutrients in the aquarium that giant clams need are calcium, strontium, iodine, and a minute amount of nitrate. Along with regular water changes the following parameters are important in keeping your Crocea Clam long term. Adding large doses weekly is not recommended. Daily doses or adding to top off water is best:
- 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. Seachem's calcium additive works at 385. 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. Use caution, as iodine spikes have been known to kill them. Add iodine with top off water or dose daily, but not at one time in a big weekly dose.
- Nitrate: They require some nitrogen for proper growth. They will not thrive at a level of 0 nitrates. Nitrate can be added if levels are extremely low, but be careful as nitrates should never exceed 2 mg/L. Provide a minute amount of nitrate that is at least 2 ppm.
Crocea 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.It is also important to make sure they are not being irritated, and not being fed upon by other organisms. Keep a watch for predators as this clam can be easy prey with its large and wide byssal gland opening.
Crocea Clams are sensitive to being handled so avoid it if at all possible. Because these clams burrow into rock and rely heavily on their byssal threads for attachment, they will eventually bore into a substrate or other substance on which they are placed. Damage could be done when messing around with an attached clam. For more in depth information on caring for Crocea Clams see, Caring For Tridacnid Clams.
- Water Changes: Bi-weekly - To keep water stable, test weekly
- Calcium Levels: 400.0 - 450.0 ppm - If using Seachem's calcium, 385 should suffice.
- Alkalinity Levels: 8.0 - 12.0 dKH - Best at 9
- Magnesium Levels: 1,250.0 - 1,350.0 ppm - Adjust magnesium levels before checking calcium levels.
- Strontium Levels: 5.0 - 15.0 ppm
- Iodine Levels: - Add iodine daily as directed. Do not add full week's dose at once (may add to top off water)
Crocea Clams can be kept in a reef environment with live rock. They should be placed on live rock or some other solid material they can attach to. Make sure if placing them in a depression of live rock that they can still fully open their shell. They can handle strong water motion and relatively strong fluctuations in water parameters, but high pH and high temperatures can cause problems.
The size of the tank should be at least 50 gallons for your Crocea Clam (though larger is better) as this will help keep water parameters stable. Live rock is necessary and sand is preferred if they will be on the substrate. A mature tank is also important. The tank should be at least 6 months old from the time of adding that last piece of live rock. Once you see Coralline algae growing (that cool pink and purple hard algae) you know your tank is doing well and ready for your clam.
When placing your clam into your tank, do not put it in a tight crevice. This may prevent it from opening fully, or if it moves too much, it can fall behind the rock work. Remove excess detritus out of hole where you place them by periodically using a turkey baster or power head.
If you have plenty of light on the substrate, placing them on a flat rock below the sand is best. Put a flat rock on the bottom glass of the tank and the clam on top of that. Stabilize the clam by filling in the area half way up the clam with sand. This will keep their large foot opening blocked off, which helps prevents pests from attacking them through the opening, and if you need to move them, the small rock makes it easier.
These clams need diligent attention paid to their water parameters, water flow and salinity, and the lighting needs to be stable. Water movement should not be a constant linear flow. Placing the clam in mild turbulent, or even "dead zones," that are exposed to strong light is best. Clams that close partially or all the way are not happy with water flow. If they are positioned where the water flow causes them to fold their mantle upward or close, this will cause the clam to eventually starve and die.
Coming from shallow waters in the wild, these clams will need intense lighting. Kelvin is best at 6K to 10K, to mimic the light levels they receive naturally in their shallow habitat. Provide very strong lighting, such as 400W metal halides or intense LED lighting if they will be towards the bottom of the tank. If you plan to keep these clams under fluorescent lighting, keep them close to the top of the tank, and the lights. Be sure to protect the lights from their inevitable squirt of water if they become startled. Once they adjust to the lighting, the light must stay constant.
If the clam is predominately brown and showing little of its normal coloration and patterning, it should be placed lower in your tank away from strong lighting. The brown coloration is the clam's zooxanthellae showing and is probably due to the clam losing its protective coloration during transport. If you need to move them, it should take a few weeks to slowly get them into their new position or you will shock them. You will see their mantle extending excessively if the light is not strong enough.
A stable salinity is critical, aim for 1.024 to prevent swinging out of the 1.023 and 1.025 range. Automatic fresh water top offs are highly suggested to keep salinity stable. Keep pH at 8.1 to 8.3, do not let the aquarium exceed a pH above 8.4. For hardness, maintain a dkh of 7.9-12, with the optimal being 9. A temperature between 74 to 83˚F (23 to 28˚C) is best, but be sure to keep the temperature you choose stable.
- Minimum Tank Size: 50 gal (189 L) - Tank should be at least 6 months old, preferably with coralline algae growth.
- Suitable for Nano Tank: No - Water will not be stable enough in a small tank.
- Live Rock Requirement: Typical Amount
- Substrate Type: Sand
- Lighting Needs: High - Strong lighting - Kelvins: 6K to 10K to mimic the light levels they receive in the shallow habitats of their natural environment.
- Temperature: 74.0 to 83.0° F (23.3 to 28.3° C) - Keep the temperature stable.
- Specific gravity: 1.023-1.025 SG - Salinity is important, too high or low a salinity can cause the death of a clam. Stay within this range, aiming for 1.024.
- Water Movement: Moderate - Crocea Clams can handle strong water motion, however high currents should not be a constant condition. Weak linear is okay, but moderate and turbulent is best.
- Water Region: All - Dependent on lighting.
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.
Crocea Clams commonly have small shrimp and crabs that live in the mantle cavity. They are considered ectoparasites or commensals, and they will not harm a healthy clam. 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.
- Venomous: No
- Temperament: Peaceful
- Compatible with:
- Same species - conspecifics: Yes
- Anemones: Monitor - Protect the clam from anemones that wander.
- Mushroom Anemones - Corallimorphs: Monitor - Safe as long as they do not come in contact with the clam.
- Leather Corals: Monitor - Should be okay if spaced apart.
- Zoanthids - Button Polyps, Sea Mats: Monitor - Should be okay if spaced apart.
- Sponges, Tunicates: Safe
- Shrimps, Crabs, Snails: Monitor - Small commensal shrimp are fine if the clam is healthy. Remove any small, rice-sized snails found on the clam's surface with a toothbrush.
- Starfish: Monitor - Starfish usually only eat dying organisms.
- Feather Dusters, Bristle Worms, Flatworms: Safe
- Clams, Scallops, Oysters: Safe
- Crabs: Safe - Commensal crabs are okay on a healthy clam
- Snails: Monitor - Make sure nassarius snails cannot turn a substrate living clam over. Remove parasitic pyramidellid snails, other snails are safe.
- Sea Apples, Cucumbers: Threat - The clam will die if these species expel their toxins. Giant clams are much more sensitive to these toxins than other invertebrates, even if the system is large.
- Urchins, Sand Dollars: Safe
- Nudibranch, Sea Slugs: Monitor - May be safe, but it is unknown if any or all species are safe.
- Copepods, Amphipods, Mini Brittle Stars: Safe
- Stony Corals: May be aggressive - Stony corals can sting your clam.
- Soft Corals: May be aggressive - Give clam plenty of space.
There are no discernible sexual differences.
The giant clams are protandry, meaning they are born male and change to female. Clams will release eggs and sperm that can number into the tens of thousands of eggs. This event tends to happen around sunset. One aquarist noted a spawning clam pulsing out eggs every two minutes. Once the eggs are externally fertilized, the embryos develop into trocophore larva, which are free-swimming. The next stage is the bivalve veliger, which sort of looks like a tiny free swimming clam. Once they are 4 to 20 mm long, they will start to burrow into the reef and begin their lives in their new home.
Crocea Clams have been propagated in captivity, and the demand from aquarists has raised interest in producing colorful varieties of all the species. Typically, there is some sort of outside stimuli that causes spawning, which can be a change in temperature, salinity, or other parameter. However this should be left to the experts, as clams spawning in a small system can cause serious pollution issues. For detailed information of tridacnid propagation, see Giant Clam Breeding and Reproduction
- Ease of Breeding: Difficult
Keep a watch out for predators! The Giant Clams can be easy prey with their large and wide byssal gland opening. The most dangerous predators are the highly prolific pyramidellid snails of the Tathrella, Pyrgiscus, and Turbonilla genera. These are parasitic snails about the size of a grain of rice or smaller, rarely reaching a maximum size of about 7mm in length. These snails attack tridacnids with a trunk-like snout called a "proboscis." They punch holes into the clam's soft tissue and then feed on its bodily fluids.
While in nature, giant clams can deal with a few of these parasitic snails, in captivity these snails tend to multiply to dangerous numbers. They may hide in the scutes of the clam or in the substrate by day, but will often will be found around the edges of the clam's mantle tissue or byssal gape (large foot hole) after the lights go out. They can produce numerous small, gelatinous, egg masses on the clam's shell. These masses are transparent, so difficult to spot. Before putting it in the tank, scrub your clam's shell vigorously with a toothbrush, or other brush with firm bristles, to remove the snails and their eggs. Be careful not to scrub the clam's soft tissues, as that can cause injury and lead to infection. Inspect your clam regularly for several months and remove any snails you discover.
Some other common ailments of Crocea Clams:
- Pinched Mantle: Another common affliction of giant clams is called the Pinched Mantle disease. The edges of the mantle become pinched and contorted, and the margins won't extend fully. This condition almost always results in death unless treated, and it can spread to other clams. The actual cause of this ailment is unknown, but it may possibly be an attack by some sort of protozoan. An easy treatment, that is is stressful but effective, is to submerse the clam in a freshwater dip for a few minutes. Signs of recovery can take a day or two.
- Bubble Mantle: Caused by laminar flow directed at the clam or pouring water directly into the aquarium in a way that causes bubbles to form (use a siphon and water pump and/or pour very slowly and carefully or pour into sump only). These bubbles can get stuck in the clam's mantle with can cause illness and death.
- Gaping: The larger of the two holes is gaping open, larger than normal. This is usually due to poor water quality. Stability of your water
Giant clams 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. Avoid large weekly doses of anything, especially iodine, which has been known to kill them. For in-depth information on potential Tridacna clam problems, see: Tridacnid Clams: Friends, Enemies & Ailments
Crocea Clams obtained from aquaculture systems are readily available, and usually from 1.25" to 2.75" in size. They can be found online and in stores, ranging in price from moderately expensive to expensive, depending on size and color.
Crocea Clams from the wild are seasonal. Because they burrow into the rock and attach themselves with their byssal threads, collecting them from the wild is more difficult and the chances of receiving a damaged clam are greater. Once the byssus gland is damaged, the clam doesn't usually live long. This is most likely due to bacterial infections, however, rather than the damage itself. You will have a much better chance of keeping a wild collected clam if you receive it still attached to a rock.
- Animal-World References: Marine and Reef
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