Purchasing Tridacnid Clams

When tridacnid clams are first imported, they generally exhibit a behaviour called "gaping". This means that the shell is fully open, the mantle is poorly extended and the inhalant siphon widely stretched. As this condition eventually passes the inhalant siphon will gape less, the shell will not be open as much and the mantle will begin to expand. If, however, the clam is kept under unsuitable light conditions, is damaged or unhealthy, this "gaping" behaviour will continue and the mantle will begin to pull inwards, shriveling and tearing between the siphons. The inhalant siphon in healthy clams can open wide at times but "gaping" results in a very wide opening and it is constantly held this way when the clam is unhealthy.

Examine the mantle closely, it should be colourful everywhere, there shouldn't be any white or clear areas; check also for rips and tears. Be aware that T. gigas may have some clear areas near the centre of the mantle, which is normal. In healthy clams the mantle should be extended over the edge of the shell and not be pulled inwards. If there are some colourless areas these could be the result of lack of light, prédation or disease. In the former case the clam should recover quickly when placed in better conditions.

Watch how the animal reacts to an external stimulus, a healthy j j specimen will respond by closing it's shell with some force (Achterkamp, 1987b). Newly imported specimens tend to react rather sluggishly but as they regain their strength, their reactions will improve.

Check to make sure the byssus gland is undamaged; there should not be any torn or loose tissue hanging from beneath the clam.

Cfoseup view oi the mantle of a There may be some byssal strands visible, but there should not be particularly beautiful Tridacna any solid tissue hanging loose. Unfortunately, byssal gland damage crocea. J.C. Deibeek. is not always readily visible and the clam will appear fine for 1 or 2

weeksj then it will suddenly die for no apparent reason. However,

Two Tridacna crocea, the one on the left exhibits gaping. J. Sprung.

Clam Byssus Gland Damage

byssal gland damage is not always fatal and we have collected and purchased several damaged clams with little loss.

If the clam has already attached itself to the substrate before being purchased, great care should be taken when detaching it. Lift the shell up gently and insert a sharp knife, razor or scissors and cut the threads as close as possible to the substrate. DO NOT cut close to the shell or you could easily cut into the extended byssal gland. If the clam is attached to a small rock or some pebbles, there is no real need to separate them. Some species such as T. crocea and T. maxima are very sensitive to being handled in this manner and they are best left attached, if at all possible.

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