jACKSON6745
The above is only my opinion from years of reading and personal observation.. If you chose not to believe me maybe you will belive a PHD who spends his life studying our hobby. Here's a quote from an article from Dr Ron:
"As reef aquarists are aware, Tridacna and Hippopus clams have symbiotic zooxanthellae located in their blood, as well as in mantle and associated with their digestive glands. Probably as a result of natural selection to maximize mantle volume, and hence increase the number of zooxanthellae carried in it, tridacnids have undergone quite an extensive modification of the basic clam structures.
In essence, while the foot and byssal glands remain ventral and in contact with the substrate, most of the other organs have been displaced by differential growth, so that the shell and mantle edges, which normally face downward in clams, are positioned upward in Tridacna and Hippopus species allowing the mantle to be facing upward so that its zooxanthellae may be well illuminated.
At this point, two statements need to be made.
The production of feeding structures, such as gills and ciliary sorting tracts is metabolically costly, it uses energy that might otherwise go into reproduction or growth.
Likewise, the mucus produced for feeding is also expensive; after all, mucous is a protein/sugar combination, and these materials could be otherwise used in building more tissues, gametes, or in basic metabolism.
From these observations, some conclusions should be obvious.
All bivalves, including those containing photosynthetic algae, need a lot of energy and materials to stay alive. Clams appear to be passive animals, but actually they are burning food at a pretty good rate. Pumping water, even by ciliary action, is expensive and they pump ALOT of water. Consequently, they need a lot of energy to survive.
Natural selection acts to minimize unnecessary costs. If clams from Tridacna or Hippopus species didnââ"šÂ¬Ã¢"žÂ¢t need to feed, the feeding structures would be eliminated. There are a number of clams that live totally on the byproducts of symbiotic bacteria living on their gills. These clams are totally gutless. The fact that every Tridacna and Hippopus individual has a good and functional feeding apparatus ABSOLUTELY PROVES that they need to feed.
Indeed this is the case, researchers have found (Klumpp and Lucas, 1994; Griffiths & Klumpp, 1996) that small Tridacna, those about 10 cm (4 inches) in shell length or shorter, simply do not have enough mantle volume to hold sufficient zooxanthellae to support the metabolic needs of the clam. Only as the clams grow larger can the zooxanthellae produce enough respiratory energy, or sugars, to keep the clams alive.
Even after this period in their lives, these clams are dependant upon captured phytoplankton for much of their needs. All animal tissue is mostly protein, and to make proteins the animals must, absolutely must, have a nitrogen source. Researchers (Ambariyanto & Hoegh-Guldberg. 1999) have found the clams depend upon their feeding to provide a nitrogen source for their own protein metabolism. Although the zooxanthellae can help with protein synthesis, the clams need a nitrogen source and that source is their phytoplankton food.
How can you tell if your clams are getting enough food?
First off, they will be actively growing. Tridacna grow rapidly if well fed, and if they have enough calcium in the water. Second, you will see them actively defecating fecal mucus rope segments. If you feed DTââ"šÂ¬Ã¢"žÂ¢s Phytoplankton or some other live plankton, you may be able to look into the clams mantle cavity, through a siphon, and see the mucus covering the gills actually lightly colored with the color of the culture. Dead, off the shelf, chemically preserved phytoplankton cultures contain mostly cellular debris and the clams will reject most of this material as it is both the wrong shape and the wrong size.
Even small clams require a lot of algal food, without which their chances of survival are marginal. Many aquarists have had the experience of keeping Tridacna alive for a few months after which they mysteriously die, after seemingly "doing well." Well... they havenââ"šÂ¬Ã¢"žÂ¢t done well, they have slowly starved to death using up all their energy reserves and finally dying. All of these deaths - ALL OF THEM - could have been prevented by adequate feeding with good phytoplankton."