Mark on Derasa Clam's Mantle

[cdw79]

Was watching my tank today and saw these two little marks on my Derasa's mantle. The areas look ever so slightly transparent when I look at them closely, but that's all I can really observe. Otherwise they just look like somewhat darker spots, but I'm positive they weren't there when I added it (about 2 and a half weeks ago).

It's always fully open, seems happy bar flipping itself 90 degrees and now back. I wondered if it was somehow an abrasion? I wouldn't think it's an issue of not enough light, as my Hydra 32's are at full blast and PAR down there was in the mid 200's. Any ideas? It's my first foray into clams so I'm still learning the ins and outs of it all. Thanks in advance!

 

[Uncle99]

Any chance you have a pic under white lights only?

 

[cdw79]

Any chance you have a pic under white lights only?

Good point, should have done that to begin with. Here it is with whites

Some googling has suggested that spots can be where a fish is picking at it, but I have watched pretty closely and haven't seen anything take any interest

 

[Uncle99]

If it was a bite, the clam would have closed up, seem to be closed more often, or close, every time a fish passes.
If light is too low, over time the mantle will starts having “white patches” within the mantle.

He seems very open and happy so just keep a watch to see what those two areas do. Should they expand and lose colour, you’ll need to bump ups light.

Below, the Squam on the left, has an example of the “white” he got shaded for a few months, so when I fixed that, it recovery over a month or so.

 

[cdw79]

If it was a bite, the clam would have closed up, seem to be closed more often, or close, every time a fish passes.
If light is too low, over time the mantle will starts having “white patches” within the mantle.

He seems very open and happy so just keep a watch to see what those two areas do. Should they expand and lose colour, you’ll need to bump ups light.

Yeah I really don't think it's a bite- the only remotely likely suspect would be my lawnmower blenny, but it's got plenty of film algae to pick at, so I'd be surprised. No angels or anything like that.

But the thought is maybe it's not getting enough light, if they ultimately get bigger? I could try ramping up my whites even more during the day but they're pretty high as is. I take it given it's a dears moving it up the scape it's a good idea? It's attached its foot to one of the rubble rock pieces I placed beneath it when I placed it in the substrate, so it wouldn't be hard, but to my understanding Derasas are specifically supposed to be in the substrate

 

[Uncle99]

Yeah I really don't think it's a bite- the only remotely likely suspect would be my lawnmower blenny, but it's got plenty of film algae to pick at, so I'd be surprised. No angels or anything like that.

But the thought is maybe it's not getting enough light, if they ultimately get bigger? I could try ramping up my whites even more during the day but they're pretty high as is. I take it given it's a dears moving it up the scape it's a good idea? It's attached its foot to one of the rubble rock pieces I placed beneath it when I placed it in the substrate, so it wouldn't be hard, but to my understanding Derasas are specifically supposed to be in the substrate

On the substrate, you are very correct.
If it’s attacked to a rock, there he must stay. Damage to the bysal thread, once attached, can prove deadly for any clam.

I d do nothing as changes induce stress, just see what develops if anything.
Stuff comes and goes all the time. Some are bad, most are just things we don’t know about our pets

I don’t have a clue what they are, but having them doesn’t necessarily mean they are bad.

No way to treat anything we can’t diagnos, maybe someone else’s has something the same.
Take your time, study and watch.

 

[minus9]

It's hard to tell with the pics, but the clam looks healthy otherwise. I agree with cranking up the whites (especially warm whites). Derasa's and the other larger clam species, squamosa, gigas will all lose their byssal threads at some point and rely on their weight to keep them upright and in place. That's why the bulk of their shells are thicker at the base and the byssal opening is rather narrow in those species, some will lose the opening altogether. Also, clams have the ability to change how the mantle works and looks based on the available light. Iridophores and zooxanthellae can move and "shape" themselves according to their orientation to light. So the appearance of the mantle can shift or change over time. As long as it's not a physical tear or laceration, you should be fine. With derasas or any tridacna clam, you should always see new shell growth on the upper margins of the shell and it should be pristine white in color. If you're not seeing new growth, you need more light (and possibly nitrogen).