So, there is no straightforward single way to always ID both species correctly, but by looking at a combination of these features you can usually figure out just about any of them. I will admit though, over the years I've come across a handful of specimens that have been quite difficult to differentiate. At such times most folks just throw up their hands and declare that a hard-to-ID specimen in a hybrid between the two species, but after doing a lot of searching, reading, and asking clam farmers questions I'm still far from convinced that these two species can/do hybridize. That's a topic for another day, though.

Aquarium Care :

When it comes to caring for maximas, water quality requirements are typical for reef aquariums in general. Basically, if you're successfully keeping corals alive and well, then your water quality is good enough for a maxima. On the other hand, if you're having problems maintaining excellent water quality - don't fool with any species of tridacnid.

When it comes to water motion, tridacnids live in reef and near-reef environments, and are regularly exposed to strong currents and wave activity. This is especially so for maximas, which often live right at the crest of a reef where waves break hardest. Thus, they are no strangers to strong, surging and turbulent water motion. However, in aquariums the flow tends to be quite linear and constant, as a pump outlet might blast water in one particular spot day and night at about the same volume per minute, and rarely creates any real surge or turbulence. So, you need to think about this when it comes to the placement of a maxima (or any other tridacnid) in an aquarium.

It's okay to expose maximas to a low velocity surge, or to turbulent flow, but putting them in a position where a pump constantly hits them with a strong, non-stop linear current is not recommended. Basically, any sort of current that causes the mantle to fold upwards too much, or over onto itself all the time is bad, as is any current that makes a specimen chronically retract its mantle. Thus, you can put one anywhere you like with respect to current, as long as it doesn't bring on either of these reactions. I'll also add that while they're almost always found on hard substrates and rubble in the wild, placing them on such is highly recommended, but is not required. Placing a specimen on sand/gravel won't kill them, but they often move around a lot, trying to find something to attach their byssus to. Next is lighting, which not surprisingly is of critical importance.

Maximas live at relatively shallow depths where they receive relatively intense light, so fluorescent lighting will only suffice in shallow tanks, or if a specimen is placed on the rockwork near the water's surface in a deeper tank. I would try fitting as many bulbs into the canopy/fixture as possible at that, and mount the bulbs close to the water, and then place any specimens within a foot of the surface, preferably less. Some specimens may be able to get by at times with less light, or further down in deeper tanks, but I implore you to not take chances. Metal halide or comparable L.E.D. lighting is your best option.

I know that some people have gotten by with less, but when it comes down to it insufficient lighting is certainly one of the most common causes of losses. The problem is that corals are very simple organisms that have no real "guts" to speak of, while tridacnids have all the organs you'd expect to find in a higher animal. They've got stomachs, kidneys, gonads, gills, and even a heart. Thus, they are far more complex than you might think, and they use a lot of calories to keep everything running. So, it's a mistake to think that just because your lighting is bright enough to keep corals healthy and growing that they're necessarily bright enough to keep a maxima alive long-term.

To make matters worse, it can take a tridacnid months to slowly starve to the point of no return. So, everything can look fine for weeks on end, then a specimen may seem to just up and die for no apparent reason when it was really starving the whole time. Every maxima is genetically different at that, and long-term experience has proven that some individuals can get by with less while others need much more, even though they may be the same species and even the same size and color. To add, you cannot give a tridacnid too much light as long as a specimen is given time to adapt to intense lighting, so it's better to err on the bright side than the dim side. For more on this, refer to my article On Lighting for Tridacnid Clams in the March 2011 issue, and for even more than that see my book Giant Clams in the Sea and the Aquarium.