<a href=showthread.php?s=&postid=10646906#post10646906 target=_blank>Originally posted</a> by Ninong
I was searching online to see if I could find that aquaculture study on baby T. maxima clams that showed that the growth rate and survival rate was substantially higher in a hatchery fed with live phytoplankton than it was in a control hatchery with no feeding of any kind but I didn't find it.
However, I did come across something interesting. Baby gigas clams get as much as 65% of their nutrition from filter feeding, falling off to 34% when they reach 10g dry weight. I guess that's still in line with the 40% figure one of the leading clam hobby experts uses because the 65% figure is for really, really tiny clams.
"Giant clams of the family Tridacnidae are familiar and conspicuous residents of shallow coral reefs throughout much of the tropical Indo-Pacific. Their most characteristic feature is the enlarged, upwardly directed and usually brightly coloured mantle, which is packed with symbiotic dinoflagellate zooxanthellae. An estimated 95% of the carbon fixed by these algal symbionts is translocated to the host (Fitt 1993, Klumpp & Griffiths 1994), where it normally provides sufficient energy to cover at least the immediate metabolic needs of the hosts (Tench et al. 1981, Fisher et al. 1985, Mingna 1988, Klumpp & Griffiths 1999).
"Giant clams are also able to filter food particles from the water column (Yonge 1936), although the nutritional significance of this has only recently been quantified. Fitt et al. (1986) first quantified ingestion and digestion of C14-labelled phytoplankton cells by Tridacna gigas, while Klump et al. (1992) showed that particulate food constituted 65% of carbon needs in small (0.1g dry tissue) T. gigas, declining to 34% in individuals of 10g weight. This capacity to exploit both heterotrophic and autotrophic sources of nutrition, plus an ability to divert an unusually high proportion of energy to growth (Klumpp et.al. 1992), are no doubt factors that have allowed T. gigas to become the largest bivalve ever to have existed."
Reference
clams are not dependent on filter feed 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 of that article 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. it also says 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 can 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 !
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
