its an old myth that clams under X" need to filter feed.
clams are not dependent on filter feeding phyto. they are primarily photosynthetic and can sustain themselves on the food provided by there zooxanthellae, through light alone. clams will extract dissolved nitrogen and phosphorus from the water and pass onto there zoox and then the zoox gives the clam sugars as food. clams will filter phyto (and bacteria and zooplankton) but when they do this all they are doing is extracting the same N & P and passing it to the zoox.
one of the arguments for feeding clams is that clams mantles are not fully developed untill they are 4" in length. this is completely false. clams mantles are fully developed and full of zoox within week of metamorphosis. another one is that clams mantles are not large enough to house enough zoox to support the clam untill its 4", false again. the size of a clams mantle is proportionate to the size of the clam through out its life.
another argument some people have for feeding phyto is that clams have a fully functioning digestive system and that if they didn't need to feed they wouldn't have this. so lets look at this. clams gills are multifunctional, they are use for respiration and capturing particulate matter. they cant get rid of the gills or they wouldn't be able to breath , clams also constantly replenish there zoox, they use their gills to do this.
the stomach is connected to the zooxanthellae tubular system (where the zoox live) the stomach passes new zoox from the gills to the ZTS , processes the sugars the zoox make (to feed the clam) and pass old, dead and un-viable zoox to the anus.
even though the digestive system isnt needed for filtering phyto, it is still used as a basic function of the clam.
if you want to feed your clams phyto, go ahead. but dont think that they will die if you dont. as long as you have strong light and N & P (fish pee and poo) in the water the clam will do just fine !
heres a few snipits from research papers to back up what i say.
enjoy
From klumpp and lucas 94
It is now established that photosynthates fixed by
symbiotic zooxanthellae are able to provide sufficient
energy to cover at least the metabolic needs of Tridacna
gigas (Fisher et al. 1985, Mingoa 1988, Klumpp
et al. 1992), T squamosa (Trench et al. 1981), T. derasa
and T. tevoroa (Klumpp & Lucas 1994
Contribution of symbiotic algae to
host respiratory requirements
The absolute amounts of carbon translocated daily by the zooxanthellae to the host (TP in Table 4) follow similar patterns of variation with size and species of clam described for P, That IS, in the smaller slze categones (0 1 to 10 g tissue weight) Trldacna gJgas has a considerable
nutritional advantage over the other 3 species, gaining 2 to 20 t~mes more energy in the form of photosynthates TP was similar in the 3 species
whlch attain 100 g In all 4 specles and size categories of clam TP was well in excess of host respiratory needs (RH in Table 4) Calculation of the percent contnbution of zooxanthellae to the host's daily carbon requirements for routine respiration (l e CZAR = (TPIRH)lOO)a, s
glven in Table 4 shows that symbiotic algae were capable of provldlng 2 to 4 times more carbon than requlred by the
host for respiration CZAR ~ncreased with clam size in all species, except in H h~ppopus, which had a comparatively
high and more constant CZAR of -340% The lowest CZAR value was
186 % in the smallest T squamosa
This study actually indicates that clams may need to acquire additional nutrients through filter feeding as they grow larger. However there zoox through photosynthesis can still provide them with at least 2x there CE needs
this study was done to determine how clams acquired there zoox and what they did with them. two sets of clams were used, one was given zoox the other was not. they were both kept in micro filtered water and not allowed to receive any particulate. the only particulate that one set received was its initial dose of symbiotic zoox. these are very tiny clams, the kind everyone says cant live through photosynthesis alone. they did just fine
http://links.jstor.org/sici?sici=00...B...size=LARGE
Fatherree 2006
"let's take a look at some CZAR and CZARG values for some small to clear up any possible confusion. the smallest clams offered for sale to hobbyists are usually in the 2.5 range, but far more "small clams" are in the 3.8 to 5cm range. keep this in mind when you see the CZAR and CZARG numbers going up.
Mingoa (1988) found that 1.75cm gigas specimens (smaller than what you can buy) had an average CZAR values of only 92% under bright sunlight. close, but not quite enough C/E from the zooxanthellae for basic maintenance. however that was in 1988 and Mingoa, using unpublished data from Griffiths, had chosen a translocation value of 32%. so you can see the same thing happening for these little clams. change the translocation value to 95% and the CZAR values will triple to 273%.
in addition, Fischer et al. (1985) reported a CZAR value for gigas (using a transference value of 95%) of 149% for 1cm specimen, 259% for a 1.15cm specimen, and 318% for a 1.55cm specimen. all smaller then what you can buy. then, Klumpp&Lucas (1994) found CZAR to be as high as 178% for 2.2cm derasa and 2cm tevoroas, with CZARG values of 140% for both, while data from Klumpp&Griffiths (1994) shows a CZAR of 265% and CZARG of 191% for 4.2cm gigas, 233% and 206% for 2.4cm crocea, 186% and 118% for 4.2cm squamosa, and 300% for 4cm hippopus"
so according to that they are getting C/E from photosynthesis just fine.
