Rock needed for Derasa ?

Fish-o-holic

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Should I place a rock under my 3" Derasa clam so it can attach? It will be placed on the substrate of the tank if that helps any.
 
Now, all I just gotta find me a nice piece of LR. TY

Just as a side note, the clam has been in my tank 2 hours and it's fully extended. YIPEEEEEEEEEEE :rollface:
 
In nature, juvenile T. derasa normally live in shallow waters attached to coral rubble. They reach sexual maturity at a shell length of more than 30 centimeters (12 inches), at which time they detach their byssal attachment. Once the byssus is detached, the water current moves them to deeper waters, where they settle on the sand and are held in place by their weight.
from here
 
at a shell length of more than 30 centimeters (12 inches), ...... the water current moves them to deeper waters
I find this a little far fetched. A clam of 30cm would weight about 35-40kg. If the water current is strong enough to move a clam of this weight, then the area is not going to be a suitable spot for larval clams to settle. Clams can however move themselves slowly by opening and closing their shell.

I would personally not bother with the live rock under a derasa. I have seen several wild derasas and the few small (<30cm) ones that I have seen only 1 or 2 were attached to the substrate. Like T. squamosa, small derasas will extend their byssal threads down into the sand giving it anchorage without being attached.
 
That was from Daniel Knop's article on derasa's. I am not going to argue it one way or another, I am just sharing the research I have done on the matter. :)
 
On a different note, why do maxima and crocea clams attach to rocks whereas other clams don't? Do they come from a different part of the ocean??? Just curious.

I'm gonna leave the Deresa as is without no rock since I can't find a small enough piece for it. I will see how the clam does over the next few days.
 
srfmon said:
My deresa & squamosa never wanted to attach to a rock or shell.
That's fine with me.
Great to hear from a Derasa owner. How long did you leave the rock under the clam and how big is the clam? I am still deciding yes or no on the rock. Dang, I change my mind fast don't I. :rolleyes:
 
Fish-o-holic said:
On a different note, why do maxima and crocea clams attach to rocks whereas other clams don't? Do they come from a different part of the ocean??? Just curious.
These are the 2 smallest species of Tridacnids. This means that even when fully grown they are not especially large animals and they attach to rock for protection against storms and waves but it also reduces the chance of parasites moving in from beneath the byssal opening. When a clam that is firmly attached to a rock shuts tightly, there is almost nothing that can get to the tissue.
Maximas do not actually bore like croceas do. They grow to about 40cm so they simply attach to a rock in a groove and they might bore slightly if the groove restricts it from opening but will generaly just stay on top of the rock. However croceas will truly bore deep in a rock and increase the size of the hole as it grows.
 
I had an 8" deresa for about 2 years before the "tank crash". It was about the size of a HUGE taco. I never tried to put it under a rock becasue it always seemed content on the sandbed.
Meanwhile my current deresa I've had for over a year now & it's about 2". I've tried the shell several times giving it a few weeks. It never liked it. The croceas & maximas are attached to shells (most of them at least) & they seemed to attach within a week or 2.
 
Hi Firechild,

I do not agree with you on two issues:

1.A Dearsa of 30cm will not weigh 35-40Kg.
I saw and lifted quite a few Derasas of the sizes 25-35Cm and I can tell ya, none of'em waz even close to these numbers.

2.Maximas do not bore in the rock like Croceas do
I saw hundreds of Maximas in the wild.
Young Maximas were always well bored into the rock.
Mature ones and mid size ones were as ya said stay on top of the rock.
The babies and young Maxima are always well bored inside the rocks

My experience is from Red Sea Maxima only, might be that in other places, things are not the same.
 
I have had a derasa for about 2 yrs now and it hates being any where but in the sand, it would constantly slam open and closed whenever I tried to put it on the rocks, The only problem with it on the sand is that it's about 8" so when a fish swims over it I have a sand storm, and corals covered with sand. I just deal with it, being its such a nice clam.
 
i just got a 3" inch dersa two weeks ago. i put in on the sand bed as you all state. i figured the same would be happy there. well it kept moving up to the front glass. so i put a few small pieces of l.r. around it and know it has attached to one of the pieces and is extending its mantle more then it ever has. i guess you could try the rock. if the clam doesn't like it you will know in a few days. jsut keep an eye on it. i feel that clams are like poeples opinions. each one is different.
 
I had a derasa for a couple of years before it outgrew a 40 gallong. went from 3 to 6+ inches. placed on the substrate directly and it would always manage to find some sort of rubble out of the sand to try and cover up the byssal opening. so maybe a small rock/stone the size of a half dollar under the sand would do the job.

edmund
 
so maybe put a small rock under the sand and let the clam decide what's best for it? That sounds like a good plan :D
 
Pfittttz said:
so maybe put a small rock under the sand and let the clam decide what's best for it? That sounds like a good plan :D
Sounds like a plan to me as well. I still am looking for that "perfect" rock for my clam. :p
 
Vili_Shark said:
Hi Firechild,

I do not agree with you on two issues:

1.A Dearsa of 30cm will not weigh 35-40Kg.
I saw and lifted quite a few Derasas of the sizes 25-35Cm and I can tell ya, none of'em waz even close to these numbers.
Lifting and guessing is far inferior to actually weighing them on a set of scales. I can tell you for a fact that that is a fairly accurate estimate maybe slightly high, it could be 30-35kg but my point still stands, that is a heavy object. I was at Orpheus Island on the GBR a few weeks ago doing an aquaculture course and we weighed and measured clams as part of a 15 yr study.
2.Maximas do not bore in the rock like Croceas do
I saw hundreds of Maximas in the wild.
Young Maximas were always well bored into the rock.
Mature ones and mid size ones were as ya said stay on top of the rock.
The babies and young Maxima are always well bored inside the rocks

My experience is from Red Sea Maxima only, might be that in other places, things are not the same.
I think you may need to reread what I said.
Maximas do not actually bore like croceas do. They grow to about 40cm so they simply attach to a rock in a groove and they might bore slightly if the groove restricts it from opening but will generaly just stay on top of the rock. However croceas will truly bore deep in a rock and increase the size of the hole as it grows.
 
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