all cukes contain a toxin called holothurin. if they die or are severely injured, they begin to release this toxin, which is similar in property to soap in that it reduces the amount of water tension in the water column. the release ofthis toxin will not effect inverts inthe tank at all, but the taxing will damagea a fishes gills causing them to be unable to take oxygen from the water, and thus the perish. not all cukes that die in captivity will release the toxin holothurin, but they all do carry it and the possibility is always there. guess you just have to ask yourself one question...do you feel lucky...punk? the most common types of death that would cause the release of holothurin in an aquarium are, the cuke gettign stung by an anemone or coral, gettign harassed by a pesky fish, and ultimately injured, crawling ove an unprotected heater and gettign burnt, and gettign killed by a power head.
there are different types of cukes as ophi stated above, and if they do have feathery tentacles around one of the ends, then they are filter feeders. Sea apples are filter feeders, and would do great in an invert only tank that was supplied with enough phyto/zoo plankton, and would be marvelous. the sand siftign cukes stay in the sandbed, and take in and from one end, extract detritus, organics, and meiofaunae and then excrete the clean sand through their anal end in the form of small pellets.
good luck
jon
