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r_gent_020898.html - Ryan Gent on Tridacna Clams - 2/8/98

Ryan Gent

Tridacna Clams in the Reef Aquarium

February 8, 1998

You can see Ryan's tank at

Hi gang...

My name is Ryan Gent. I've been keeping Tridacna clams for approximately ten

years and I would like to share some of my experiences and opinions.

Biological Classification:

Tribute: Mollusca

Class: Bivalvia (mussels)

Order: Veneroidea (venus mussels)

Family: Cardiacea (heart shaped mussels)

Subfamily: Tridacnidae (giant clams)

Genus: Tridacna and Hippopus

The six species of clams commonly available to the aquarium industry are:

Tridacna gigas - up to 3' long

Tridacna derasa - up to 2' long

Tridacna squamose - up to 16" long

Tridacna maxima - up to 14" long

Tridacna crocea - up to 6" long

Hippopus hippopus - up to 16" long

Other species not usually available to the industry:

Tridacna teveroa - up to 20" long

Tridacna rosewateri - up to 6" long

Hippopus pocellanus - up to 16" long

Physical Characteristics :

Tridacna clams are more advanced organisms than corals since they possess

gills, an esophagus, a mouth, a stomach, two kidneys, both male and female

gonads when sexually mature, muscles for closing and opening of the shell and a

foot for attaching the clams to rocks.

They posess an intake siphon and an exhalent siphon. The intake siphon is the

larger opening and is located above the byssal opening on the bottom side of the

clam. The exhalant siphon is the smaller tube projection extending from the

mantle itself.

Tridacna clams are hermatypic; that is they possess zooxanthellae algae in their

tissue with which they live in a symbiotic relationship. The algae are not in the

cells of clams like they are with corals. Instead, they live in a special symbiont

channel system. The channel system proceeds from the stomach to the mantle

and this is the means by which juvenile clams are innoculated with zooxanthellae


Care and Feeding :

Care of the clams varies with species, size and age.

Tridacna derasa, squamosa, gigas and Hippopus hippopus are the easiest to


Because of their large size, Tridacna gigas and derasa should only be kept in

large aquariums since they can get to about 12" in 5 to 7 years.

Tridacna maxima and squamosa are fairly easy to keep.

Both may have sizable byssus openings and will partially burrow into the rock or


Tridacna crocea is probably the hardest to keep and has the largest byssus

opening, making it susceptable to attack by predators.

Tridacna crocea may burrow entirely into rock or corals.

Older clams and juvenile clams (smaller than 2") can also be difficult to keep.

They seem to be more sensitive to environmental changes and conditions.

This may be due to undeveloped or aged conditions of the clams themselves.

Alternative feeding may be beneficial to these clams more so than others.

Food sources, other than the light for the zooxanthellae algae, can be

phytoplankton and zooplankton from the tank itself.

Or it can be prepared food, preferably very small in the 5 - 20 micron range.

Other food sources may be urea, or ammonia as a nutrient for the clam's

zooxanthellae colonies.

Adding directly or through large schools of fish is best.

Algae cultures seem to work well for food source, however, be careful not to

overload your filtration system.

Also, watch out for unwanted algae blooms due to fertilizers used for the


Tridacna clams are non-aggressive although they may overgrow other

organisms or disturb neighbors by belching (expelling water out of their siphonal

opening in powerful bursts).

Localized bleaching may be caused by shading by other organisms, drastic

changes in light levels, or major temperature fluctuations (temp over 88-90 or less

than 68-70 degrees Fahrenheit).

Generalized bleaching may be caused by lack of nutrients to zooxanthellae

algae, lack of light and heavy metal poisoning.

Toxins or excessive metals, excessive Iodine levels (over NSW .06 mg/l) or high

phosphate levels may affect clam health.

Clams are sensitive to high or low salinity levels (should be kept between 1.023

and 1.026 specific gravity or 31 - 35 ppt salinity).

Clams should be burped - any time a clam is out of water, care should be taken

to get all of the air out when it is placed back into the tank.

Fine air bubbles in the water from pumps may irritate the clams.

Predators and Parasites :

Possible fish predators of clams may be :

some wrasses, angels, butterflies, triggers, neon gobies and blennies.

Possible snail predators of clams are "rice" snails (Pyramidellidae) and Muricidae


Rice snails can reach sexual maturity in 40 - 45 days and have a life span of 4 -

  1. months.

Rice snails may also be found on other species of snails including Turbo and

Vermetidae snails (mucous web snails).

Parasitic Rice snail-eating wrasses recommended by Dr. Carlson from the

Waikiki Aquarium are Halichoeres melanurus, Halichoeres argus and Halichoeres


Parasitic Pea crabs, Xanthasia murigare, may be found on the gills of Tridacna

clams and they can also come under attach from some kinds of shrimp, crabs,

worms, boring sponges and algaes.

Introduction to your tank :

Tridacna clams prefer good light but acclimate them slowly.

Brightly colored clams usually develop better color under more intense light.

They also prefer very slow water movement, not enough to move their mantle

around too much.

They also prefer to be placed in an upright position with their intake siphon the

same or lower than their outlet siphon.

Because of their calcerous shell, calcium, strontium and carbonate levels should

be maintained and monitored to Ca = 400+ dkh = 7 - 9 and about 8 mg/l


Tridacna clams are also sensitive to high pH levels usually anything over 8.3.

A range of 8.0 to 8.2 is preferred.

When detaching a clam from a rock, try to cut the byssal threads as close as

possible to the rock (as far away from the clam itself as possible).

Just pulling the clam off may damage the clam and cause death.

When placing clams on rock, try to fit the byssal opening onto the rock as tightly

as possible so predators cannot get inside the clam.

Do not restrict the clams opening and closing motions.

Some clams will not hook to the rock; this is usually due to byssal thread mass

inside the clam.

When purchasing clams, check their response to shadows.

Listlessness is probably a sign of a hurting clam.

The information I've shared with you here is only food for thought.

Nothing is concrete, ideas are always changing and opinions vary considerably

within the trade.

Thank you for having me as a guest speaker.

Q: Should the clams be placed on rocks or sand? Or does it matter?

Crocea and maximas should be on rocks. Squamosa, derasa and gigas on the

sand. Juvenile squamosas should be on rocks as well.


Q: Which wrasses are predators?

Tough question...

Fish can vary from specimen to specimen. I've had bad luck with wrasses in

general so I don't usually keep them with the clams unless they serve a purpose.

I have a leopard wrasse in my system. Have also kept six-lined wrasses safely.


Q: How does a person "burp" a clam after it has been out of the water?


Rolling the clam while underwater several times to make sure that all air bubbles

are released.

Air bubbles can be detected by lumps in the mantle tissue. <RG>

Q: What's your definition of "intense" light? Watts? Color temp? Bulb?

FOOTNOTE: Air bubbles can really be dangerous to clams.

250 watts and up is best, 6500 to 10000 kelvin color temp. I use Iwasaki 6500K

and a 10000K from another manufacturer that I can't recommend.

Make sure to acclimate the animals slowly. <RG>

Q: Is it alright if the clam has a small stone that is lodged up inside the byssus

opening. The clam appears to think it is attached to a rock and hence does not

emit byssus threads. Is this ok? Or could that cause future complications?

It can cause future complications. As the clam gets largers, the opening will get

larger and the opening will then be accessible to predators. <RG>

Q: Can an "ugly" clam become better looking if placed close to the MH's?

No. Bleached areas will "color-up" but colored areas will not necessarily get more

colorful. <RG>

Any recommendations on how to remove said stone in previous question?

V-E-R-Y carefully... Try to pull the rock gently enough to cut the byssal threads

next to the rock and as far away from the clam itself as possible.

By gently pulling and holding, the clam will start to relax. <RG>

Q: What is the connection between gaping and a healthy clam?

A healthy clam will be respondent to shadow (waving your hand over the clam)

whereas a gaping (unhealthy) clam will be sluggish in response. Also, mantle

extension should be normal for that particular species.


Q: Is there any farvoite food clams have?

Food particulates under 30 microns. I use zooxanthellae cultures for mine. Knop

mentions using blood and yeast but I don't have any experience with those



Q: Will clams die if they lose commensal algae? Is it possible to re-introduce

algae? How done?

Yes, clams will die if they lose their zooxanthellae and it is not replaced. Yes you

can replace the algaes and yes you can culture these algaes outside of the


I just finished developing a culture from a 12" Red Sea max. <RG>

Q: How small would a Squamosa be to be considered a juvenile?

Under 5", squamosas would be considered juveniles. <RG>

Q: I had a maxima clam for 3 months on the sand substrate - base in info from

Knopp, I moved it up 6" onto a crevice on a rock. It died 3 days later. I realize this

is not extensive information, but do you have any ideas?

Is it possible that the clam settled into the crevice so that it could not open

entirely? This can cause suffocation. <RG>

<SPS> This is an assumption, but are most clams that are over 4" considered to

be fully developed, and hence don't have to depend as much on planktonic life?

SPS: yes that's a reasonably good rule of thumb.

<SPS> ok, thanks

<jake> how many clams can be keep in a 75 gal tank?

<Marty> How do you think croceas and maximas would fair under the german

175W 10K bulbs?

jake: depends on the species... (1) gigas... <g>

Marty: fine

<SPS> Marty, they do just fine :)

<Marty> Where can a hobbyists purchase zooxanthellae cultures? Or how does

a hobbyists create zooxanthellae cultures ?

Marty: Zoox cultures are not commonly available yet in the hobby. Culturing is

very difficult and labor intensive.

<Marty> I can attest to Iodine killing clams. I accientally overdosed Iodine once

and lost 5 clams in a week.

Marty: Watch the coris as it matures for possible attacks on the clam.

<Big> Ryan does the ridges mean anything, I have had the Max in the bottom for

about a year now

Big: Are you asking about the flutes on the shell?

<Big> yes ryan

<coral> can 2 max. 2"&4" survive in my 29 gal. with only 4 20w norm. flor.?

<Marty> Ryan - What do you use for filtration? Would you recommend skimming?

Carbon? Ozone?

<critter> What type of supplemental food an be prepared to promote clam growth

The ridges are natural. On some clams species, they are larger and more

pronounced. Wild croceas will have smaller flutes as they typically get worn off as

the clam bores into the rocks or coral.

<TomVeil> one at a time folks ;-)

coral: you would probably need more light.

<Marty> Ryan - What Sr test kit do you use? I've tried Salifert, and it is a

complete pain in the butt!

<coral> are supp. feeding needed if there's not enough lighting?

Marty: I use heavy protein skimming and carbon once a month.

critter: algae cultures and rotifers are the only two that I am aware of.

critter: I also prepare my own food which is ground up VERY finely.

<Gnat> When feeding the clam does "feed the water" or the clam directly?

Big: I can be reached at

Thanks for the talk Ryan!

Created by liquid
Last modified 2005-02-07 05:54