Sea cuke defensive chemistry is pretty well known. There are a variety of saponins (soap-like chemicals) in the skin, and some more specific and toxic chemicals that are often specifically assciated with the Cuvierian tubules (these tubules are associated with the hind gut of sea cucumbers, and are thought to be primarily defensive in function). It is the release of these chemicals that is likely to have the disasterous effects mentioned earlier in the thread.
Let's back up a step. When a cuke is stressed, it can react in a variety of ways. First, like other echinoderms, they have a compound in their skin called catch collagen -- this tissue is under neurological control and is capable of changing from a 'liquid' to a 'solid' form very quickly. This is one of the coolest things about echinoderms in general, and is how cukes manage to get themselves into tiny holes in rocks - they goopify their bodies, pour themselves into the hole, and then solidify their skin to prevent extraction. The same is true of urchin spines, star legs, and so on... Sorry, getting off track... The cuke can react to stress by either becoming flaccid and goopy, or by ejecting all the water from its system and becoming a small, hard turd-like lump. Either of these responses is typical of animals that have been harmlessly disturbed (e.g., poked with a finger or such) or moved from one tank to another.
A second, and more drastic response is evisceration. In this case, the cuke simply expels a portion of its digestive system (guts) onto the substrate. Evisceration can be induced in a variety of ways (e.g., chemical stress, physical manipulation, crowding, etc.), and include some or all of the digestive system (and in some cases other organs such as the respiratory tree and gonads), but is not necessarily accompanied by chemical discharge, thus even stressed cukes that puke out their intestines may not have much of an impact on your aquarium, depending on the situation. Despite the fact that this stress response may not wipe out your tank, it is not trivial however, the cuke loses it's digestive capacity in the process and although it can regenerate the gut, it needs time, and excellent water conditions to do so. I suspect that most cukes that die in the aquarium have been mishandled along the way to the point that they have eviscerated, and the repeated insults of moving and rough handling between collection and placement in our tanks does not fall under the category of ideal conditions for regeneration....
The most likely problem for your tank as a whole, however, is when a stressed cuke expels its Cuvierian tubules (a series of long, spaghetti-like tubes leading off the hindgut at the base of the respiratory tree -- remember my post to Bretton about sea cukes breathing through their butts?) by rupturing the hindgut, because this is almost always accompanied with the release of a soup of defensive chemicals that are likely to seriously impact, and potentially wipe out an enclosed tank.
Of course the ambient levels of chemicals and the exact identity and toxicitiy of them vary from species to species, and the general statement made by Charles that the "turd cukes are less toxic than the colorful filter feeders" is a pretty reasonable generalization (or at least the concentrations and variety of toxic chemicals in the Aspidochirotiacea is generally lower than those of the Dendrochirotacea), but there are plenty of exceptions, and the fact that there is a behavioral component makes it impossible to predict the effect of any given cuke in any given tank when something particular happens.
Hope that clears things up...
Last modified 2006-11-24 18:41