Related FAQs:  Tridacnid Identification, Tridacnid Behavior, Tridacnid Selection, Tridacnid Compatibility, Tridacnid Systems, Tridacnid Lighting, Tridacnid Placement, Tridacnid Feeding, Tridacnid Disease, Tridacnid Disease 2, Tridacnid Health 4, Tridacnid Health 5, & Tridacnid Reproduction, Giant Clams, Tridacnids 2, Tridacnids 3, Tridacnids 4, Tridacnid Clam Business,  Bivalves, Bivalves 2, Lighting Marine Invertebrates, Related Articles: Got Tridacna? A beginner's guide to keeping Tridacnid clams by Laurie Smith, Example Chapter from NMA Reef Invertebrates book, on Giant Clams, A Brief Guide to the Selection and Placement of Tridacnid Clams by Barry Neigut, Tridacnid Health: Pinched Mantle Syndrome in Giant Clams by Dr. David Basti, Deborah Bouchard & Barry Neigut, Bivalves, Mollusks, Lighting Marine Invertebrates,  /The Conscientious Marine Aquarist Top Tridacnids Select the right clams for your reef aquarium, and provide the right setting for them to thrive.

by Bob Fenner

 

            Giant Clams have been cultured for the hobby for about thirty years and times before and currently (unfortunately) wild-collected. This family of Mollusks has an assortment of size species that occur in a myriad of colors. Liking reef-quality conditions, they are not hard to keep; providing sufficient nutrition directly and via photosynthesis, avoiding pests, parasites and predators; keeping water quality stable and optimized for their use. This being stated, many Tridacnids are too-easily lost. This survey article is my attempt to provide the highlights for successful husbandry of these Bivalves.        

            Many Tridacnids (Family Tridacnidae ARE the giant clams) are lost due to starting too small/stressed/starved, being placed with inappropriate tankmates, and kept in too-chemically-clean and/or mineral-deprived systems.

Which one? A few inch specimen, or? Knowing which species is best for you, how to pick out the best specimens for your system, and how to care for it is what we’re about here.

 

 

Selecting: Three requirements

1)      Aquacultured: Don’t buy wild collected Tridacnids unless that’s all that is available… They are almost always inferior to captive-produced; too often have unwanted hitchhiking pests; and are FAR more likely to perish due to stress, poor adaptation to aquarium conditions.

2)      Size Matters: Just like the Goldilocks/Tres Bears and porridge temp. story, there are definitely Clams that are too small, and on the other end of the scale too large. BEWARE of tiny clams… ones below two inches or so die like proverbial flies. Reciprocally, large clams don’t ship all that well, and are quite expensive… so, you want to purchase yours between two plus and four minus shell width ideally.

3)      Health: Obviously you want to avoid unhealthy specimens. Ascertaining which to buy in  this regard requires knowledge, keen observation and patience. You NEED to know what non-diseased Clams look like and how they behave (see diseases below)… and CAREFULLY look over prospective purchases; scrutinizing ALL individuals in the tank, or the entire sub-system of tanks if they are tied together plumbing-wise. Beware of obviously pinched mantles, animals that aren’t open/ing, ones that don’t respond to shadows and changing currents near them.
In particular: Beware of Gapers! Indicated by a stretched appearance or splaying of the animal’s shell halves, as well as the inhalant siphon (the larger opening on the mantle of this filter-feeder) appearing to be open particularly wide and non-responsive.

 

 

Top Tridacnids Used in the Hobby/Trade:

Tridacna derasa, Tridacna squamosa and Hippopus hippopus are the hardiest members of Tridacnids for aquarium use; though a few others do come into the market at times.

Giant clams are mostly identified on the basis of shell characteristics, shape/symmetry, ribs/folds/scutes, the shell halves upper margin and presence and characteristics of their byssus (attachment organ at the base)

Hippopus hippopus: Horse’s Hoof, Bear Paw… Clam:

            Very thick shell with prominent ribs
            Conservative mantles that don’t extend beyond edge of shells
            Most occur in colors of brown, tan, or green with gold highlights
            The incurrent siphon of this species is smooth (lacks “tentacles”)
            Live on the substrate and prefer intense light and moderate current

A wild-collected Hippopus specimen in captivity. Aquacultured individuals have cleaner, more defined shells.

 

Tridacna crocea: Boring (as in burrowing) Clam:

            Smallest Tridacnid used at six inches maximum
            Shells have a narrow, naked profile allowing for their burrowing habit
            Release acid to melt rock, and opening, closing of shells to burrow.
            Attach to rock with their large byssus
            Occur in blues, green, browns… expensive ones have brilliant blue with gold highlights
            Most nowayears are wild-collected in Vietnam… Many of these die mysteriously.

A couple of examples of Croceas in the wild; two blue specimens in Queensland, Australia, and a brown individual in S. Sulawesi, Indo.

 

Tridacna derasa: Southern Giant or Smooth Giant Clam

Derasas are the hardiest and most widely available of Tridacnids.
Grow to two feet across in the wild; and quickly in captivity.
Mantle colors include tans, orange, blues, black and white; and usually there’s a spotted, wavy pattern at the mantles edge of blue or green.
This is the only Tridacnid with a small, narrow byssal opening.
Shells have six or seven vertical folds and can close shells completely.
Best to place midwater (in rock recess) or on the bottom in the sand.

Tridacna derasa in the wild: Below left and lower in Fiji on rock and on sand, and a close up, below right, showing details of the mantle (S. Leyte, Philippines)

 

Tridacna maxima

Maxima clams have elongated shells that lack symmetry.
They have narrowly spaced scutes on the outer portions of their shells.
Maximas occur in a myriad of colors and patterns; mostly blue, gold and green.
Maximas attach to hard substrate with their byssal threads and are better purchased with
some hard material attached to this organ.
Maximum size in the wild is about a foot across.
May burrow into soft rock over time;, take care not to damage the byssus.

A couple of burrowed in Maximas below (Red Sea on the left, Wakatobi, S. Sulawesi, Indonesia on the right); and two aquacultured ones at a LA wholesaler in the ideal four inch size range. Note the PVC pipe pieces to set them up off the substrate, prevent damage to the byssus.

 

Tridacna squamosa: Scaled Clam

            The common name is in reference to having large scutes over its symmetrical shell. 
            Wide to small byssal opening that only weakly attaches to solid substrates.
            Gold, tans to yellow; occasionally all blue. Highlight color spots of blue, orange, yellow

Some Squamosa examples; below at left and lower in the Red Sea, and below right in the Maldives; all showing the prominent shell scutes indicative of this species.

 

Stocking:

            Photo-adaptation is critical, particularly for small/er specimens. Often you can’t tell just how much light quality, intensity and duration your clam/s have become used to ahead of your acquiring them. The best course of action for you and your new Tridacnids here is to start off with lower values of all three measures of light and increase them over a few weeks’ time. IF you don’t have lighting that’s easy to adjust in terms of brightness, nor depth that allows you to place the clam/s lower; consider using layers of shade-cloth to shield a percentage of incipient light.

 

Compatibility: Some fishes and invertebrates are sure to possible no-no’s to keep with Tridacnids. Many mid-size to larger Wrasses will nibble on their mantles. Triggers may eat all soft parts up with glee; and larger fishes period like groupers and morays are so unaware of their environment that they may knock your clams off their perches. Butterflyfishes, Angels and others may cross the line and start picking on your clams. Similarly large crustaceans like crabs and lobsters, and even some shrimps can prove troublesome; bugging the clams by walking over and outright sampling them. Stinging-celled life; aka “corals” to most hobbyists, can sting Clams. Keep them a good foot or more away to prevent sweeper tentacle contact.

What is the “cost of freedom”? Answer: Constant vigilance. Even with careful selection, starting with smaller tankmates it is critical that you keep a sharp eye out for developing trouble.

 

System: As mentioned above; Tridacnids require reef-system conditions; including water quality, currents, lighting and feeding; both chemical and biological/particulate.

            Make it Used: Established, optimized set ups are necessary. It may take half a year or more to be sure you’re ready for a clam. The healthy production of encrusting red algae is a good indication of readiness.

            Biominerals and More: Healthy Tridacnid Clams are very big users of biominerals; you will need to monitor and very likely adjust the concentrations of Calcium (380-450 ppm); Magnesium (about three times your Calcium concentration) and Strontium (6-10 ppm; no more) for their health. Bear in mind that elevated temperature and intense lighting can greatly boost the uptake of these alkaline earth elements. Best to incorporate a working “calcium reactor” using media that melts down to provide all; or pre-mix and use dried/concentrated supplements for ready use.

            Biomineral content will do you no good without matching alkalinity; 8-12 dKH is an ideal range for these animals and all other reef life.

            Iodine (actually –ide, -ate) is an essential micro-nutrient as well. You want 0.04-0.08 ppm present; though in actual practice adding a dose every week, along with water changes will very likely suffice.

Placement: Where you put these animals is very important. Note from the scant species coverage above that some live on amongst or on rock, others on the sand/substrate. There’s more to this simple difference however. The amount of light should be measured and added to if necessary, the animals placed lower in the water column or light-screened if too intense. Place your Tridacnids to face up toward the light.

            Circulation needs to be considered as well, and these animals prefer moderate (5-10 times turnover where they are) per hour or so; not too little/stagnant, nor too brisk. In particular beware of placing clams in direct pump blast of water movement.

 

Foods/Feeding/Nutrition:

            Small clams (under two inches across; that you should be avoiding) do need direct supplemental feeding. Larger specimens should do fine on photosynthesis along with incidental food from your feeding other livestock and life originating in the system (DSB, LR, LS). There are some commercial clam food products and promoters of their use (the same folks for the most part) that you can offer your clams if you’re so inclined, concerned that they’re not getting sufficient nutrient.

            There is a deficiency syndrome we should mention as it is in particular, a common mortality cause of captive clams et al. chemo-photo-synthetic life. Many reef systems are kept “too clean” via the use of chemical filtrants… removing all measureable nitrate, soluble phosphate and more from the water; denying absolutely essential elements. These animals NEED some NO3 and HPO4 present to live. IF you must use chemical filtrants, do so sparingly and on a punctuated basis (on/off) every few days; ALWAYS assuring there is some measurable nitrate and phosphate.  

 

Disease/Health: Tridacnids are one of only a few groups of marine invertebrates that “give signs” that something is going wrong. A lack of responsiveness, gaping, or loss of color are prompts for you to be checking water quality, doing water changes; possibly adding nutrients to the water.

Pinched Mantle: caused by a Protozoan that can be eradicated by a 25 minute pH adjusted aerated RO water bath.

 

            Browning out, or loss of mantle color is often due to aging light bulbs, but can be sign of a nutrient or biomineral deficiency.

Clam Pests & Predators: Many pests and predators are attracted to Tridacnids. Boring sponges, segmented worms (Errantiate polychaetes), crabs, predatory mollusks (snails) and flatworms are commonly caught preying on Tridacna. Most can be observed through careful observation and removed recommended. Pyram, Murex and Costellarid snails often prey on such clams. The Pryamidellid snails are perhaps the most common, prolific and tedious, if not difficult, to eradicate due to their small size and camouflage coloration. Natural predators, such as smaller species of wrasses, can be helpful for reducing the population of such predators, but none can be assured of providing complete protection.

A pic of the base of a Tridacnid showing an infestation of Pyramidellid snails.

 

            The best means of their control is of course avoiding introduction period. This can be assured by purchasing cultured specimens IF these have not been housed in a system that also harbours wild individuals. Better by far to be safe than later sorry; by doing your own isolation of new purchases for a few weeks; particularly if dealing in wild stocks. I should state that the need for quarantine also applies to live rock, live sand, actually any other source of life with hard substrate involved that has been wild-extracted or come in contact with the same.

 

Cloze:  

            Mention other species and hybrids.

Giant clams are not only beautiful, but they are beneficial to captive systems; removing ammonia, nitrate, phosphate and other organic materials in the course of their filter feeding and photosynthesis.

            Make the effort to find and choose captive produced over wild-collected specimens. Most of the Tridacnid clams found in the ornamental trade are cultured, although some still extracted from nature. Aquacultured animals are much more likely to excel; they are easier to acclimate for having been farmed in captive conditions and transported with fewer traumas.

            Pay attention to your clam/s… Most issues are water quality related and show early in non-opening, tired looking mantles. Be quick with checking your water, changing some out and adding a double dose of iodide/ate and all should be well.

 

A Gigantic Tridacna gigas; close to five feet across with a shell that weighs hundreds of pounds. Some institutions keep these monsters. Some outfits sell this species to hobbyists… I wish they wouldn’t.

                        

 

Giant clams are from the family of Tridacnidae, and come in an assortment of different sizes and colors. They have been cultured for the hobby for about 30 years, but unfortunately, they are also still collected from the wild.

This family of mollusks enjoys reef-quality conditions and are not hard to keep, but you must provide sufficient nutrition directly and via photosynthesis; avoid keeping pests, parasites and predators with them; and maintain stable water quality.

Many Tridacnids are lost due to selecting specimens that are too small, stressed or starved from the beginning; being placed with inappropriate tankmates; and being kept in water that is chemically stripped or devoid of minerals.

This article will provide the highlights for successful husbandry so that you may increase your chances of success with these beautiful bivalves.            

 

Choose Well

1.      Go Aquacultured

Don’t buy wild-collected Tridacnids unless that’s all that is available. Wild-caught specimens are almost always inferior to captive-produced. Too often they have unwanted hitchhiking pests and are more likely to perish due to stress and poor adaptation to aquarium conditions.

2.      Size Matters

Beware of tiny clams -- those below 2 inches or so die like proverbial flies. Conversely, large clams don’t ship all that well, and are quite expensive. Purchase clams between 2 and 4 inches in shell width.

3.      Healthy Choices

Obviously, you want to avoid unhealthy specimens. Ascertaining which to buy in this regard requires knowledge, keen observation and patience. You need to know what healthy clams look like and how they behave (see diseases below). Look over prospective purchases carefully and scrutinize all individuals in the tank, or the entire sub-system of tanks if they are tied together plumbing-wise. Beware of obviously pinched mantles, animals that aren’t opening and those that don’t respond to shadows and changing currents near them. Most of all, beware of gapers! Gapers are indicated by a stretched appearance or splaying of the animal’s shell halves, as well as the inhalant siphon (the larger opening on the mantle of this filter-feeder) appearing to be open particularly wide and non-responsive.

 

 

Top Tridacnids

Tridacna derasa, Tridacna squamosa and Hippopus hippopus are the hardiest members of Tridacnids for aquarium use, but a few others do come into the market at times.

Giant clams are mostly identified on the basis of shell characteristics (shape, symmetry, ribs, folds and scutes), the shell halves upper margin, and the presence and characteristics of their byssus (attachment organ at the base).

Horse’s hoof / bear paw clam (Hippopus hippopus)

            • Very thick shell with prominent ribs.
            • Conservative mantles that don’t extend beyond edge of shells.
            • Most occur in colors of brown, tan or green with gold highlights.
            • The incurrent siphon of this species is smooth (lacks “tentacles”).
            • Live on the substrate and prefer intense light and moderate current.

(Temperature, pH and alkalinity requirements for this species?)
<All Tridacnids are the same: spg 1.025-6, pH 8.2-8.4, Alk.: 2.5-4 meq/l>

 

Boring (as in burrowing) clam (Tridacna crocea)

            • Smallest Tridacnid used at 6 inches maximum. (What do you mean by smallest used? That people should not select one smaller than 6 inches? Or they don’t come in sizes smaller than 6 inches?)

<Three inches is ideal… too much smaller ones are very touchy and larger cost too much>
            • Shells have a narrow, naked profile that aids in burrowing.
            • Release acid to melt rock, and opening, closing of shells to burrow. (This is confusing. The acid opens the shells to burrow? Or that is a separate action – they open and close their shell during the burrowing process?)

<The clam produces and releases the acid to help bore the hole in the rock to live within. The shell opening/closing helps grind the opening>
            • Attach to rock with their large byssus.
            • Occur in blues, green and browns. Expensive ones have brilliant-blue color with gold highlights.
            • Most are wild-collected in Vietnam, and many of these die mysteriously.

(Temperature, pH and alkalinity requirements for this species?)

<The same as stated above… Calcium 350-400, Magnesium at about three times the concentration>

 

 

Southern giant / smooth giant clam (Tridacna derasa)

• Derasas are the hardiest and most widely available of Tridacnids.
• Grow to 2 feet across in the wild, and quickly gain size in captivity.
• Mantle colors include tan, orange, blue, black and white. Usually possess a spotted, wavy pattern at the mantles edge that is blue or green.
• This is the only Tridacnid with a small, narrow byssal opening.
• Shells have six or seven vertical folds and can close shells completely.
• Best to place midwater (in rock recess) or on the bottom in the sand.

(Temperature, pH and alkalinity requirements for this species?)

<Ditto>

 

Tridacna maxima

• Maxima clams have elongated shells that lack symmetry.
• They have narrowly spaced scutes on the outer portions of their shells.
• Occur in a myriad of colors and patterns, mostly blue, gold and green.
• Maximas attach to hard substrate with their byssal threads and are better purchased with
some hard material attached to this organ.
• Maximum size in the wild is about a foot across.
• May burrow into soft rock over time; take care not to damage the byssus. (How can it become damaged? How can it be protected?

<The byssal threads are easily broken and crushed by dropping, placing the clam on a hard surface… s/b placed on a PVC pipe pedestal>

(Temperature, pH and alkalinity requirements for this species?)

<As stated: Reef conditions>

 

Scaled clam (Tridacna squamosa)

            • The common name is in reference to having large scutes all over its symmetrical shell. 
            • Wide to small byssal opening that only weakly attaches to solid substrates.
            • Color comes in gold, tan to yellow, and occasionally all blue. Highlight color spots of blue, orange and yellow.

(Temperature, pH and alkalinity requirements for this species?)

 

 

Stocking

            Photo-adaptation is critical, particularly for smaller specimens. Often, you can’t tell just how much light quality, intensity and duration your clams have become accustomed to before you acquired them. The best course of action for you and your new Tridacnids is to start off with lower values of all three measures of light (What are the three measures of light? Suggest appropriate starting values for each.)

<Permanent PAR values of 100-200 are about right; best measured w/ a meter at depth>

and increase them over a few weeks. If you don’t have lighting that’s easy to adjust in terms of brightness, nor depth that allows you to place the clams lower, consider using layers of shade-cloth to shield a percentage of incipient light.

 

Compatibility

Some fish and invertebrates should not be kept with tridacnids. Many mid-size to larger wrasses will nibble on their mantles. Triggers may eat all soft parts up with glee; and larger fish, such as groupers and morays, may knock your clams off their perches. Butterflyfish, angels and others may cross the line and start picking on your clams. Similarly, large crustaceans like crabs and lobsters, and even some shrimps, can prove troublesome, harassing the clams by walking over them or picking at them. Stinging-celled life, such as some corals, can sting clams. Keep them a good foot or more away to prevent sweeper tentacle contact.

Even with careful selection and starting with smaller tankmates, it is critical that you keep a sharp eye out for developing trouble.

 

System Setup

As mentioned above, Tridacnids require reef-system conditions, including water quality, currents, lighting and feeding -- both chemical and biological/particulate.

Established, optimized setups are necessary. It may take half a year or more to be sure you’re ready for a clam. The healthy production of encrusting red algae is a good indication of readiness.

Must-Have Minerals

Healthy tridacnid clams are big users of biominerals. You will need to monitor and very likely adjust the concentrations of calcium (380-450 ppm), magnesium (about three times your calcium concentration) and strontium (6-10 ppm; no more) for their health. Bear in mind that elevated temperature and intense lighting can greatly boost the uptake of these alkaline earth elements. Best to incorporate a working “calcium reactor” using media that melts down to provide all (as in all of the minerals mentioned – calcium, magnesium and strontium, or to just provide all the calcium your clam needs?)

<Using “reef” based media; all three biominerals can and will be supplied in proportion. Otherwise folks can use specific supplements>

 or pre-mix and use dried/concentrated supplements.

Biomineral content won’t do you any good without matching alkalinity. An ideal range for these animals and all other reef life is 8-12 dKH.

Iodine is an essential micronutrient as well. You want 0.04-0.08 ppm present, but in actual practice, adding a dose every week along with water changes will very likely suffice.

 

Appropriate Placement

Where you put these animals is important. As I mentioned previously, some live among or on rock, and others on the sand/substrate; however, there’s more to this simple difference. How light reaches these places must be considered. Measure the amount of light and be sure to add to if necessary for the animals placed lower in the water column. Always place your Tridacnids to face up toward the light. Conversely, be careful not to provide so much light that your tridacnid becomes stressed and rarely opens its shell. (I added this. Is it OK? If so, how can you measure to make sure there isn’t too much light? )

<Ah yes; fine. And you can measure PAR/PUR with a meter; borrowed from an LFS, club or purchased>

Circulation needs to be considered as well. These animals prefer moderate (five to 10 times) water turnover per hour. Beware of placing clams in the path of a direct pump blast of water movement as this can cause them stress.
<Yes>

 

Nutrition Needs

Small clams, which you should avoid if less than 2 inches across, need direct supplemental feeding. Larger specimens should do fine on photosynthesis along with incidental food from your feeding other livestock and life originating in the system (DSB, LR, LS – what do these abbreviations stand for?).

<Deep Sand Bed, Live Rock, Live Sand>

There are some commercial clam food products that you can offer your clams if you’re concerned that they’re not getting sufficient nutrients.

There is a deficiency syndrome we should mention, as it is a common mortality cause of captive clams and other chemo-photo-synthetic life. Many reef systems are kept “too clean” via the use of chemical filtrants (should this be filters or no?),

<Mmm; no; just as is: filtrants… these are media>

 removing all measureable nitrate, soluble phosphate and more from the water. This process, unfortunately, also removes essential elements (minerals?)

<Just as is: elements>

 in the process. These animals need some nitrate and hydrogen phosphate present to live. (How does it help them?)

<Numerous ways metabolically; but w/o, can’t form, add shell mass>

 If you must use chemical filtrants, do so sparingly and on a punctuated basis (on/off) every few days. Always make sure there is some measurable nitrate and phosphate left.  

 

SIDEBAR: Watch for Health Problems

Tridacnids are one of only a few groups of marine invertebrates that “give signs” that something is wrong. A lack of responsiveness, gaping or color loss are prompts for you to check water quality, perform water changes and possibly add nutrients to the water.

Browning out, or loss of mantle color, is often due to aging light bulbs, but the condition can be sign of a nutrient or biomineral deficiency.

 

SIDEBAR: Beware the Pests & Predators

Many pests and predators are attracted to Tridacnids. Boring sponges, segmented worms (Errantiate polychaetes), crabs, predatory mollusks (snails) and flatworms are commonly caught preying on Tridacna species. Most can be observed through careful observation and removed.

Pyram (Is this a common name or a genus?),

<Genus (sorry), Pyramidellidae is the family name>

 Murex and Costellarid snails often prey on clams. The Pyramidellid snails are perhaps the most common, prolific and tedious, if not difficult, to eradicate due to their small size and camouflage coloration. Natural predators, such as smaller species of wrasses, can be helpful for reducing the population of such snails, but none can be assured of providing complete protection.

The best means of their control is, of course, avoiding introduction in the first place. Only purchase cultured specimens (of clams?).

<Yes>

 Try to avoid those that have been housed in a system that also harbors wild individuals. By quarantining new purchases for a few weeks, you can avoid introducing predators into your tank.

I should state that the need for quarantine also applies to live rock, live sand and any other source of life that has been wild-extracted or come in contact with the same.

 

Choose Wisely for Success

Giant clams are not only beautiful, but they are beneficial to captive systems, removing ammonia, nitrate, phosphate and other organic materials in the course of their filter feeding and photosynthesis.

Make the effort to find and choose captive-produced instead of wild-collected specimens. Most of the tridacnid clams found in the ornamental trade are cultured, but some still extracted from nature. Aquacultured animals are much more likely to thrive; they are easier to acclimate because they have been farmed in captive conditions and transported with fewer traumas.

For the best results, pay attention to your clams. Most issues are water-quality related and show up early in non-opening, tired-looking mantles. Be quick with checking your water, changing some out and adding a double dose of iodide/ate and all should be well.

 

Robert Fenner is the author of multiple aquarium-related articles, studies and books. His work in the industry spans decades, and his teaching and academic credentials include several degrees in chemistry, physics and biology. To contact Bob, visit webwebmedia.com.