Clams for Rent

 

Over the years, Andrew at Polo Reef has curated a diverse collection of clams from various species and origins. Despite meticulous care, including different quarantine methods and lighting variations, maintaining them long-term has proven challenging. This struggle echoes among fellow hobbyists, reflecting a shared frustration with clam longevity in aquarium settings.

 

Driven by this conundrum, I embarked on a quest for understanding, seeking wisdom from esteemed peers and authorities in the field. Through candid conversations with great minds like Julian Sprung, Andrew Sandler, Claude Schumacher, Danilo Ronchi, Sanjay Joshi, and James Fatherree, I gained invaluable insights not readily found in conventional literature. Their collective wisdom offers a beacon of hope, guiding us towards a future where keeping clams will no longer be an unattainable feat.

A pivotal moment in the evolution of Tridacna clam husbandry coincided with the emergence of sps corals in our hobby landscape. Approximately thirty years ago, enthusiasts welcomed these majestic creatures into their ecosystems with open arms. However, by the late 1990s, a stark reality dawned upon us as Tridacna clams, once readily available, teetered on the brink of extinction due to unsustainable harvesting practices. Despite their endangered status, a glaring incongruity persisted: while revered as a sushi delicacy, Tridacna clams faced prohibitive bans in the aquarium trade.

 

Yet, adversity often breeds innovation, and the tide began to turn with the visionary endeavors of entrepreneurs who recognized the value of these clams. Their efforts in developing sustainable farming techniques welcomed a new dawn for clam farming. Today, there are clam farms in the Indo-Pacific, from Tahiti to the Red Sea. Decades of research and dedication has even led to the establishment of closed aquaculture facilities.

Despite the remarkable strides made in clam farming, why do numerous hobbyists still struggle to maintain them long-term? The complexities underlying this challenge extend beyond a singular cause, encompassing a multitude of factors. One frequently overlooked aspect is the vulnerability of byssal threads. In the early stages of their development, Tridacna clams anchor themselves to substrates through delicate byssal threads, produced at the clam's base.

 

While some species, such as Tridacna gigas and derasa outgrow their reliance on these threads as they mature, others continue to utilize them even at saleable sizes. The issue arises when clams are uprooted from their substrate, causing tears in the byssal threads. This seemingly innocuous damage sets the stage for infection, precipitating a slow decline in clam health over weeks or months. Regrettably, discerning between healthy and damaged byssal threads poses a challenge, particularly when procuring clams from online sources. Fortunately, advancements in our understanding have mitigated the frequency of such damage during clam relocation, thereby diminishing its contribution to their demise.

A common cause of clam mortality is our misunderstanding of their light needs and optimal placement within the tank. While they derive some nutrition from feeding, clams primarily rely on light as their energy source. Despite assuming they require conditions similar to corals, species like crocea and maxima often need higher light intensity. Originating from reef environments, clams require more nourishment than our tanks can provide, making light crucial. Inadequate light leads to a slow decline in health and eventual death, even if some energy needs are met through food.

 

Optimal light intensity ranges from 250-350 PAR for Crocea and maxima, with slightly lower levels required for the other species. Placing clams at the tank bottom, where light is insufficient, can lead to their decline. Visible growth, with bright white shell emerging, indicates adequate light and nutrition. Conversely, a dirty or yellowish shell signals the need for adjustments to prevent the clam's demise.

 

Placing clams on the tank bottom can contribute to their demise for several reasons. First, this location often lacks adequate light, especially detrimental for species like crocea and maxima, which prefer resting on hard calcium substrates. These clams can dissolve the substrate to anchor themselves firmly in place, earning them the nickname "boring clams”. Furthermore, placing clams in sand or at the tank bottom exposes them to potential predators like snails, predatory flatworms, and bristle worms.

 

Despite efforts to control these pests, even small numbers can pose a significant threat to clams. Predatory snails from the Pyramidellidae family can also quickly kill clams if introduced. To mitigate these risks, proper placement of clams and the elimination of predators are essential for their long-term survival. Larger clams may fare better when placed on the substrate, provided no predators are present. Regular inspection and removal of predatory organisms, along with the introduction of natural predators like wrasses, can help maintain a safe environment for clams.

 

While recognizable issues like light and placement contribute to clam mortality, unseen pathogens pose an even greater threat. Bacteria such as Acinetobacter, Enterobacter, Plesiomonas, Pseudomonas, Xeromonas, and Vibrio have been identified as particularly harmful to clams. Unfortunately, detecting these pathogens without specialized equipment is nearly impossible, and they can proliferate rapidly in aquarium conditions, overwhelming a clam's defenses. Signs of infection may include slight gaping or minor mantle necrosis, though sometimes there are no symptoms until it's too late.

     Although treatments like amoxicillin dips show promise, their effectiveness is still under evaluation. Bacterial infections are often seen in newly imported clams, possibly due to stress and overcrowding, emphasizing the importance of quarantine and testing before introducing them to a tank. An example of the devastating impact of bacterial outbreaks is seen in Andrew's experience, where pathogens wiped out almost an entire clam population despite quarantine efforts. Understanding these pathogens better will improve quarantine and treatment methods, ultimately benefiting all hobbyists.

 

 

Clams face a hidden threat from protozoans, particularly those of the Perkinsus family, which can cause "pinched mantle" disease, characterized by the mantle folding back on itself. Untreated, affected clams typically perish within days. While some suggest antibiotics, freshwater dips have shown effectiveness against these pathogens. To administer a freshwater dip, match the dip water's temperature, pH, and alkalinity to the tank environment. Submerge the clam for thirty minutes, gently shaking it to ensure water penetration. Rinse it in clean saltwater before returning it to the tank, repeating this process two more times over the next few days.

 

 The treatment above applies to both bacterial and protozoan infections, with signs of recovery typically appearing after three treatments. Freshwater dips may seem unconventional, but clams have a natural tolerance to freshwater, potentially making this treatment effective against pathogens intolerant to it. While T. maxima and crocea clams are most susceptible to protozoan infections while gigas, derasa, and squamosa are less so. Considering the high mortality rate of newly purchased clams, adopting freshwater dips upon arrival may mitigate risks, especially as beautiful clams often succumb to infections soon after purchase.

 

 

	Type of clam	Years Kept	Lighting	Cause of death
Sanjay	Squamosa	5	LEDs	Unknown
Sanjay	Gigas	7	LEDs	Still alive but suffering bubbles in the mantle
Julian	Mixed	6	Sunlight	Addition of new clam
Andrew	Mixed	1<	Halide/LED	Unknown
Mike	Gigas	7	Sunlight/LED	Inadequate light
Danilo	Mixed	5	LED	Bacterial
Claude	Mixed	5	Halide/LED	Bacterial

 Gas Bubble Disease

    Recently, Sanjay reported a problem with his gigas clam that has not been reported often.  The T. gigas that had been housed in his tanks for at least seven years, was showing bubbles in its mantle, which were preventing the clam from extending its mantle fully. This clam had been housed in two tanks, both under LED lighting, and a variety of water conditions and had never shown this condition before.  Bruce Carlson had seen this condition before and attributed it to hyper-photosynthesis occurring in the clam, which needed shading. Andrew also reported that when he had seen this condition his clams eventually succumbed to it. Sanjay had not changed any factors in his tank and his lighting schedule has been intense, but constant for the entire time that the clam has been in the tank. The only change that occurred in the tank was the addition of ammonia, but this had been occurring for over a year before this condition occurred.    

 

When reviewing the literature there is some support that these bubbles are not oxygen bubbles from photosynthesis but may be nitrogen bubbles occurring from the water being supersaturated with nitrogen and oxygen gas. These bubbles have been reported to be taken up by clams in commercial environments when the water was supersaturated with gas. This can occur from cavitation from water pumps or from changes in temperature. This problem may be more of a problem than it appears on the surface. With the use of more and bigger pumps, and related plumbing there is a good possibility that there are more dissolved gases in our tanks than ever. These bubbles may not just be oxygen, but also nitrogen, which dissolves in water at approximately the same rate as oxygen. Since very few hobbyists measure the total gas pressure (TGP), the total dissolved gas in a tank, it is likely that this problem may occur more frequently than we realize. While it may not kill clams directly it may irritate and stress them enough that they are susceptible to the other factors described.  Prior to their being banned from our tanks, it seemed that they were much easier to keep long-term. During this time many of us also used smaller pumps and trickle filters, which were great degassers. So it could be possible that these factors kept extra nitrogen and oxygen from being dissolved in the water in our tanks. It will be interesting to see if this condition persists if TGP is reduced or in Sanjay’s case when the temperature becomes more stable.  The clam is currently stable, but Sanjay is keeping a close eye on it lest this condition worsen.

One often overlooked factor contributing to the difficulty of keeping clams is gradual starvation. While clams are often likened to corals in terms of their nutritional needs, they are more complex organisms with higher nutritional requirements. In low-nutrient reef tanks, particularly those with low fish populations, the sources of nitrogen and phosphorus necessary for clam nutrition may be limited. The question of whether clams need to be directly fed is subject to debate and varies depending on several factors. Sufficient light, fish load, and nutrient levels all play a role. In tanks with adequate or high fish populations that are well-fed and well-lit, direct feeding of clams may not be necessary.

 

However, in tanks with low fish populations, insufficient light, or low nutrient levels, supplemental feeding may be required. Clams are not selective eaters; they consume phytoplankton, zooplankton, bacterioplankton, and detritus, provided it is of the appropriate size. If it becomes evident that the tank lacks sufficient nutrients for the clams, there are commercially available foods designed specifically for them. These should be used sparingly and as a supplement to the overall diet provided to fish and corals.

 

 

    (Two of the giant clams that were 12” across being kept in the Penn State tank circa 2002)

 Conclusion

Clam mortality isn't confined to any region; European colleagues face similar challenges. This suggests issues with both local suppliers and clam farms. While we've identified some factors, like those mentioned earlier, there's still much we don't understand. Additional concerns are constantly emerging. By addressing known factors and minimizing predators and pathogens, clams should thrive in reef aquariums. However, like early coral diseases we are only starting to scratch the surface on their causes.

 Julian’s clam in his outdoor saltwater pond in sunlight

 

I extend my gratitude to Andrew, Julian, Sanjay, James, Claude, and Danilo for their contributions. For those interested, I recommend James Fatherree’s book, "Giant Clams in the Reef Aquarium," second edition. As I researched, my previous ignorance about clam mortality became evident. Armed with newfound knowledge, I aim to transition from renting to investing in their long-term health. I hope this article sparks dialogue and inspires us to keep these creatures thriving for decades.