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Genus Tridacna
By: Gene Schwartz |
Cover Photograph
Genus Tridacna
By: Gene Schwartz
Photo by Gene Schwartz
One of the most fascinating and incredibly beautiful creatures that I ever kept in aquaria has to be clams from the family Cardiacea (heart shaped mussels), particularly from the genus Tridacna. They have been called "Jewels of the Sea" by many and one look at the colorful mantles of T. crocea or T. maxima clams can explain why it is so and why they are so popular and kept by many aquarists. I personally find them to be pretty hardy animals and relatively easy to keep, providing that one would get familiar with their requirements and provide them with a suitable captive environment to live in. One source of good information about giant clams is the book by Daniel Knop, "Giant Clams".
One of the very first requirements for keeping Tridacna clams successfully in captivity is proper illumination of the aquarium. Without going into much detail about various lighting schemes and various bulbs (given the scope of this short notation for the cover page), I would say that in my experience I've had the most success by utilizing metal halide bulbs in the full daylight spectrum in combination with some fluorescent actinic bulbs (VHO).
It goes without saying that most of us, if not all, are trying very hard to maintain proper water parameters, i.e. closely matched to NSW. This usually means that we use all sorts of equipment and filtration methods to keep nitrogen and phosphate contents as low as possible. It is the very first requirement in keeping successful reef aquaria and today most of us are pretty successful at it. :-) However, one must understand that extremely low nitrogen and phosphate concentration in water is not all that good for the clams. According to Daniel Knop in his book "Giant Clams", sometimes seemingly inexplicable deaths or bleaching of mantles can possibly be attributed to low nitrogen levels. If you intend on keeping large population of clams in aquaria, together with some delicate stony or soft corals, it may be difficult to achieve a perfect balance. Tridacna clams house about ten times more symbiotic algae (zooxanthellae) than corals per surface area (C.Belda, pers.com. 1994). This raise in number of symbiotic algae is possible because clams have a specialized symbiont channel system in their mantles, this also raises the output of the photosynthesis but it also results in much higher nutritional demand. I am not trying to say that one has to have high concentration of NO3 or PO4 in the tank to successfully keep Tridacna clams, slightly higher levels of NO3 than are normally considered perfect for the coral reef aquarium would be enough to keep your clam happy. To put it in numbers, I think 3-5ppm of NO3 would be a pretty good target and won't turn your Acroporas into brown sticks. It does not mean that one should/would abandon their husbandry routine or forgo water changes in order to keep higher NO3 levels. It simply means that one should consider the possibility that large numbers of Tridacnas in an aquarium can strip it of nutrients pretty quickly.
Photo by Scott Zachow
Another difficult balance to achieve when trying to house clams and stony corals like Acropora species together is water movement. Lighting requirements are mostly similar for these animals but the water currents needed to keep them happy and healthy are very different. Turbulent water movement that is favored by most Acropora corals could be quite disturbing for the clams and can lead to their demise since they are unable to move to a better location on their own. Constructing some type of barriers to break up the currents in the tank and provide some shelter for the clams helped me alot in keeping clams and Acroporids together in the same tank.
One thing that both these animals have in common is that the demand for calcium and carbonate are much the same and it was easy for me to satisfy by utilizing calcium reactor. Large number of clams and Acroporas in the same tank can raise the demand pretty high and it becomes very difficult to satisfy that demand after a while. So, one must consider carefully the number of clams for their aquarium and take into consideration equipment that one has for addition of calcium and carbonate.
In conclusion, I must say that keeping Tridacna clams in my aquarium added certain challenges but it also added unbelievable beauty and a touch of exotic to it and I wouldn't think of keeping a reef aquarium without having these "jewels" in them.
Gene Schwartz
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