Deresa Clam question.



Quick question for the knowledgeable members here.
My deresa clam opens up wide but his mantle isn't expanding outwards the way it used to be... should I be concerned? My crocea is doing awesome so I can't figure it out yet...

bang guy

A couple notes:
First, make sure it has that white rim of new shell that indicates it is growing. If it's growing it is probably fine.
Watch to make sure nothing is picking on it and there are no pyramid snails ( I'm sure you've already done this).
It could be that it is getting more than sufficient lighting and is just retracting a little to regulate the amount of light it gets.


Hey bang guy - no white rims... I'm concerned now...
no pyramid snails.
I'm going to try to move it and see if this changes things... thanks for your reply!


New Member
Does your clams mantle show any signs of fading coloration? How about signs of gapping? Does it react to light alterations? What are your calcium and alkalinity readings? Do you supplement your clams diet with phytoplankton? Is something bothering your clam?
These questions being answered can help determine if, in fact, you have a real problem, plus helps to ensure your clams health for years to come.


As mentioned, I'd check for "gaping" (the clam holding its incurrent siphon open wide). Some species, such as T. crocea are "naturally gapy", but T. derasa is not.
Have you changed anything in your tank (new additions, moved the clam, additives, changed the flow pattern, etc)?
What is your temp and pH...I can tell you that IME, most tridacnids don't appreciate water swings or temps above 80*F in captive systems.
What's your Ca level? Clams need at least 400 ppm of Ca in their water which they use to build new shell.
Is the clam on the substrate? T. derasa
is a substrate dweller that relies on its weight to remain in place. If so, check its byssal area for bristleworms...sometimes they can irritate a clam so it doesn't extend its mantle (I had one like this in the past).