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Tridacna

Tridacna is a genus of reef-dwelling giant clams. They are known as giant clams or killer clams - because legend has it that they will trap and drown divers underwater with their shells, but in reality the animals are much too slow to do this. They have scaly shells with several corrugations and a mantle that fills the shell opening and, depending on the species, can stretch wide open, because this is where symbiotic algae, the zooxanthellae, are located, with which the giant clam carries out photosynthesis. The mantle seam also contains light-sensitive organs that cause the clam to flinch when shaded. The closing reflex is a good sign of a healthy clam; diseased specimens cannot close tightly. Also noticeable is the mouth opening, through which the mussel constantly pumps water and expels it through its siphon on the opposite side to filter food particles such as phytoplankton.

On the underside is the byssus opening, where a gland secretes adhesive threads with which the mussel attaches itself to the substrate - the associated muscle is an archilles heel for the mussel, as tearing it out often means death for it, which is why the byssus threads should always be cut off with a blade and the mussel thus gently and non-violently detached from the substrate. Depending on the species, the mantle is colored beige to brown - which is often called gold - to bright blue. The special thing about the coloration of giant clams is that the blue color is not caused by pigments in the classical sense like many others, but by structural patterns that change the wavelength of light by refraction. They thus belong to a whole series of animals and plants that produce blue coloration in this way - other well-known examples are butterfly wings or peacock feathers. The iridescent blue colors therefore depend on the viewing angle and are always most intense when viewed from above - as in our photos. When viewed from the side, they can appear quite a bit darker, so it is best to place the animals so that you are looking at them as steeply as possible. The specimens described by wholesalers as "green" or "pink" are not the bright blue ones, but usually the term is rather exaggerated and they are in reality rather gray. Reds, in particular, simply do not occur in Tridacna; you are more likely to be looking at a "golden" animal with its shell shining through its mantle.

Tridacna need a position with solid ground on which they can attach themselves, we offer extra clam holders here. The lighting may be almost arbitrarily strong, giant clams show almost no photoinhibition with intensive lighting, they can get by with weak light as well, though. At a size of 5 cm and more, feeding is usually no longer necessary, below that it is best to feed several times a week with phytoplankton - preferably live - which also contributes to the vitality of larger animals. The current should be gentle, the mussels are insensitive to high nutrients. All Tridacna species are covered by the Washington Convention on International Trade in Endangered Species of Wild Fauna and Flora, and specimens in the trade are usually from aquaculture or mariculture farms. Rumors of "wild-collected" Tridacna from the South Seas stem from the culture method used there with so-called collectors, in which the wild larvae are offered artificial settlement substrates onto which they prefer to settle - the young mussels are then raised in mariculture. A similar process is common in oyster farming. The CITES regulations do not anticipate this method of propagation, which is why they then classify these farmed animals as "wild".

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