At the same time we purchased our Nassarius snails, we also purchased a Sea Cucumber.
This particular type of sea cucumber is called a Tiger Tail Sea Cucumber. They range from gray to brown, depending on the specific type of species and are covered in spines called papillae. Their maximum size in a reef aquarium are 12 – 18 inches, and in the wild get as long as 6 feet! They are omnivores (eating both meat and plants) originating from the Indo-Pacific oceans. We purchased this one to help clean up the detritus on our sand bed. The general rule about stocking a reef tank with sea cucumbers, is to have no more than 3 inches of cucumber to 20 gallons of water. They also need fine sand (sugar or slightly larger) and prefer a deep sand bed. Another interesting tidbit; sea cucumbers breath through their anus!
There are a three main types of sea cucumbers; filter-feeding, deposit-feeding, and medusa worms. The Tiger Tail is a deposit-feeding sea cucumber that takes sand in through a mouth at one end, and deposits clean sand castings out the other end. If sea cucumbers are not getting enough food, they will shrink in size. This is one of the first signs that there is not enough food present to sustain the sea cucumber. Sea cucumbers can go for quite a length of time without eating and are capable of digesting themselves to ward off starvation. It is important that we note what size he is initially, and keep an eye on his size (when we see him), as well as look for the presence of castings.
The coolest feature about sea cucumbers, is their ability to change the consistency of their bodies. Their body tissue is controlled neurologically, allowing them to make their body rigid, or very soft. This is how they can get themselves into very tight spaces. For example: they can literally drain themselves into a hole much smaller than they are, and then make their body rigid so they can’t be pulled out. A great defence mechanism if you ask me!
There is a second defence mechanism in where a sea cucumber violently ejects their “guts” (all or a portion of the fore or hind gut). Sea cucumbers can regenerate these “guts”, but need quite a bit of time to do so. This expulsion is why many aquarists won’t put sea cucumbers in their tank. When certain species of sea cucumbers expel their Cuvierian tubules, which is essentially a defence organ, there is a soup of toxic chemicals that are also released. This is what is known as “cuke nuke” among aquarists. These type of chemicals can kill fish if not handled in a timely manner. That being said, a sea cucumber will only release these tubules when the sea cucumber feels very threatened. The chances of this happening are pretty low from my reading.
In the unlikely event that this would happen, performing large water changes, heavy skimming, and running a carbon filter will help to remove the toxins and cause little damage to the reef if caught quickly.
We discussed all of this with our LFS prior to purchasing the sea cucumber, and was told that yes, it is a possibility with some species of sea cucumber, but very unlikely with a Tiger Tail.