Keeping the Derasa Clam

Just about any reef aquarist will, at some point, wish to keep tridacnid clams in their system. Their colors rival those of any coral. They have an incredibly exotic appearance (even their shells look cool). And (at least for most tridacnid species) they may be kept on the bottom over the substrate, which is a spot where relatively few corals can go. 

But perhaps one thing that makes these mollusks so desirable to hobbyists is their more stringent husbandry requirements and perceived delicateness. While that may seem counterintuitive to many people, any aquarist knows how irresistible a rare or difficult species can be. Aquarists love challenges, and the satisfaction that comes with successfully keeping nominally sensitive livestock is the ultimate achievement. 

That being said, it’s always best to work your way to the top. Before anything else, this generally means lots and lots of research. And then yet a bit more research. Then, many of us start modestly and carefully by trying our hands at a similar but hardier species.

In the case of tridacnid clams, many would say that such a “starter species” would be the Derasa clam (Tridacna derasa). The derasa’s lovely smooth shell and golden wavy lines on its mantle can provide a bold focal point in any display. While it is certainly a demanding aquarium animal (arguably, all bivalve mollusks are), it is considerably easier to keep than some of its “fancier” cousins such as the maxima clam (T. maxima). In fact, it is advisable to keep a derasa clam for some time (minimally a few months) to ensure that you, and your tank, are ready for the more sensitive types.

This article explains how to get off to a good start with T. derasa.

Prepping for a Derasa clam

Derasa clams will usually adapt well to any system that is housing healthy and growing SPS corals. Thus, if your acros are looking sweet, you’re probably ready to get your Derasa.

The Derasa clam often loses it byssus gland (which makes the threads by which tridacnid clams attach to hard substrates) early in its life. In these cases, it might position itself on a sandy bottom with little or no attachment. This trait makes it simple to place in an aquarium, either on a substrate or bare bottom. While this species can really go anywhere in the tank, a bottom placement makes sense for the reason that it cannot harm itself from falling. If you intend to keep a Derasa higher up (e.g. on the hardscape), we recommend supplying it with a well-fitted base such as the Clam Rock.

Don’t make the mistake of underestimating how much light this animal needs; it utterly depends upon its photosynthetic symbionts (the same dinoflagellates as in photosynthetic corals) for survival. To be clear, T. derasa requires intense, full-spectrum illumination. But, thankfully, it is just a wee bit more tolerant of suboptimal light conditions than T. maxima or T. crocea. 

Water flow isn’t a huge issue with these clams. Derasas are even less picky in this regard than their cousins are. Just be sure that each specimen is receiving enough water movement to refresh its immediate environment while avoiding powerful, direct jets of current. 

Finally, when selecting a decent, permanent plot for your clam, be sure that it is fully clear of sweeper tentacles from nearby corals. 

Maintaining a Derasa clam

If you are careful to (1) provide bright light, (2) maintain great water quality and (3) place the clam in a cozy spot, then there isn’t much else you’ll ever have to do to keep your clam alive and well. Indeed, the best conditions for derasa clams (and for all tridacnid clams) are stable conditions. Unless there is some obvious problem to remedy, it’s always best to leave them alone (don’t move an established clam around unless it’s clearly necessary!). 

In the right conditions, the clam will obtain most of its nutrition from its symbiotic algae. However, providing live plankton for these filter-feeders can certainly improve their health and increase their growth rates! This appears to be especially so with younger specimens. For this, a high-quality, nutritionally balanced live phytoplankton such as OceanMagik is ideal. 

With its nutritional needs properly met, and with a steady calcium level of 400-420 ppm, a derasa clam can grow surprisingly quickly; a well cared for juvenile can easily double or even triple in size within a year! Ultimately, your clam will reach a length of around 20 inches (the second largest of the giant clams!).

Conclusion

Tridacna derasa is an excellent choice for your first tridacnid. For sure, you should be able to keep one of these beauties before moving on to the yet touchier members of the genus. This hardly relegates derasas to some status as a “second-rate” tridacnid clam; to the contrary, they bear incredibly beautiful coloration and also build one of the prettiest shells. In the right environment, this clam can grow to become a truly impressive centerpiece worthy of admiration from newbie and pro aquarist alike.