Holothuria atra

Acclimation: sea cucumbers are sensitive to changes in salinity. Acclimate it slowly by drip in a separate container, then move it without pouring the shipping water into the tank. Handle it as little as possible and with gloves: handling or relocating it can by itself trigger the release of holothurin.

Setup: it lives in the open, on sand; provide a large area of fine sand and medium water flow. Do not overstock: the usual rule of thumb is about 7.5 cm (3 inches) of sea cucumber per 75 litres (20 gallons), and an average reef tank can only feed one or two.

Fit every pump, powerhead and overflow intake with a large, securely fixed strainer: according to Rob Toonen, most 'cuke nukes' happen when a sea cucumber is sucked in and shredded. If it happens anyway, remove the animal at once, make a large water change, increase skimming and add activated carbon.

Tankmates and sensitivities: keep it with peaceful companions. If it expels its organs, it rarely regrows them in an aquarium. Spawning in the tank is a sign of stress, not of good health. Like other invertebrates, it tolerates neither copper treatments nor high nitrate; never put it in a copper-treated tank, not even in quarantine.

For you: sea cucumber toxins (saponins such as holothurin) irritate skin and mucous membranes; eye contact can cause serious injury, including blindness in reported cases. Wear gloves when you work in the tank. Water: aim for 22 to 25.5 °C, a specific gravity of 1.023 to 1.025, pH 8.1 to 8.4 and 8 to 12 dKH.

It is a deposit feeder: it swallows sand, digests the organic film on the grains (detritus, bacteria, diatoms, microalgae) and leaves clean sand behind in small casts. If you no longer see casts, it is not finding enough food.

In the wild it sifts the sediment with its tentacles and digests the detritus and organic matter. In the aquarium it depends on detritus-rich sand: a well-established, regularly fed tank produces more of it. None of the sources consulted names a supplementary food specific to this species.

Watch its size: a sea cucumber that slowly shrinks is starving, even if it looks active. Do not add it to a new, very clean or bare-bottom tank, nor over coarse gravel: it needs fine sand (sugar-sized or finer) in a well-established tank.