Holothuria (Mertensiothuria) hilla

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: a large tank with a deep sand bed and rocky caves where it can anchor itself. In aquaria most individuals reach 30 to 45 cm. 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.

Sensitivities: this is one of the more active species, so it is more likely to run into a poorly guarded intake. Like other invertebrates, it tolerates neither copper treatments nor high nitrate; never put it in a copper-treated tank, not even in quarantine. An individual that shrinks or no longer leaves sand casts is not eating enough.

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.