Re:Tank mishap, miracle survival, and maybe some luck

Pete Giwojna

Dear Carrie:

Sea cucumbers can be fascinating aquarium inhabitants and useful sand sifters in the right system, and I’m happy to hear that yours survived his stranding and emerged unscathed from the ordeal.

Holothurians or sea cucumbers are echinoderms, close relatives of the starfish and sea urchins. They have the same pentameral, or 5-sided, radial symmetry as sea stars and sea urchins, which is most evident as the five rows of tubefeet that run longitudinally down their long, wormlike bodies. They are simple sessile animals that have no brain, heart, or eyes, breath through their anus and often entertain houseguests therein (e.g., pearlfish , commensal crabs, and parasitic snails, all of which are allowed to nibble freely on their innards) and routinely disembowel themselves in response to stress. Their mouth is located at the opposite end of their bodies from the busy (and oft crowded) anus and is surrounded by branching, sticky, mucus-coated tentacles, which can lengthen or shorten dramatically, and are used to sweep or mop up the substrate, gather up all manner of dead or decaying organic matter, and pass it into their mouths. Basically, they consume organic detritus and ingest fine-grained sands and sediments to digest off the bacteria, microalgae and diatoms that cover the surface of each sand particle.

It sounds like that was indeed a lucky day for both you and your fortunate cuke. Not only did you stumble onto a wonderful new aquarium system for a bargain price, but your sea cucumber stoically endured the stress of being left high and dry without resorting to any of its extraordinary defense mechanisms, which can often cause trouble for the aquarist when they are employed. Sea cucumbers can be problematic aquarium specimens under certain circumstances because of their many unusual defense mechanism, which may sometimes have an adverse impact on their tankmates, as described below:

(1) Evisceration or autovisceration: they may forcibly eject all of their internal organs through their anus, presumably to distract predators while the cuke makes a slow-motion getaway. This act of voluntary disembowelment surprisingly does the sea cucumber no permanent harm, as the internal organs are regenerated over a period of months, but it gives a new meaning to the phrase "puking your guts out." Spilling their guts in this fashion is a response to a life-threatening situation — predation, chemical stress, low oxygen levels that cannot support them — and can help the sea cucumber survive until conditions are more favorable. No chemical discharge normally occurs when they eviscerate, so this odd behavior is not a threat to the aquariums inhabitants.

(2) Regurgitating Cuvierian tubules — glue traps. At the slightest provocation, some cukes expel masses of very strong, long, extremely sticky, filamentous threads (Cuvierian tubules) to deter predators. Other animals, especially spiny crabs, become hopelessly trapped in these adhesive tubules and the more they struggle, the worse they become entangled until they are as incapacitated as if they were wrapped up tightly in a straight jacket. Once trapped in this sticky web, they are doomed to a slow death. The hobbyist can intervene to save the entrapped animal(s), of course, but disentangling them by hand is a painstaking process that can be the devil’s own business.

(3) Animated Goop — morphing into tight places. Some cukes can more or less liquefy their bodies (a process that hobbyists often refer to as "goopifying") in order to ooze or pour themselves into the tighest cracks, crevices, and hidey holes for protection. Once they’ve holed up in this manner, they inflate their bodies with water and solidify their skin again, wedging themselves tightly in place to prevent their extraction. A harmless enough trick, you might think — until the tight space they wedge themselves into and plug up is the intake, drain, or overflow of their aquarium! To prevent this sort of accident, aquariums that house Holothurians should be cucumber-proofed, a task most seahorse keepers have already accomplished in order to prevent their ponies from being suck up by filter intakes and overflows.

(4) Chemical Warfare — the dreaded "cuke nuke!" Some sea cucumbers release toxins (holothurin and holotoxin) while alive when threatened (or even after death, in some cases). These toxins can be quite deadly to fishes but don’t seem to affect most invertebrates. The group of colorful sea cucumbers known as Poison Apples are the worst offenders in that regard, and a large specimen is said to be able to release enough toxin to kill all of the fishes in a small, closed system aquarium and wipe out the entire tank. Such rare Holothurian-related aquarium accidents have become known as "cuke nukes," an unfortunate appellation that has given all sea cucumbers a bad reputation with hobbyists.

This is regrettable because the beneficial Aspidochirotiacea burrowing and deposit-feeding sea cucumbers are such good sanitation engineers and are much less likely to find themselves in a situation where they must call their defense mechanisms into play, and far less likely to cause ANY trouble than their toxic cousins, the Poison Apples. Still, any aquarist who is considering adding sea cucumbers to his tank should be aware of the potential risks. Anyone who is contemplating cukes should read Rob Toonen’s excellent series of articles about them, which outlines the benefits and risks they may pose in greater detail. It is available online at the following URL:

Click here: Aquarium Invertebrates

Best wishes with all your fishes (and invertebrates), Carrie! Here’s hoping your super cucumber continues to live long and prosper in your aquarium.

Happy Trails!
Pete Giwojna

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