Black sea cucumber (Holothuria atra) care guide

Group
Other invertebrates
Other names
Lollyfish, Holothuria (Halodeima) atra, Black cucumber
Family
Holothuriidae
Origin
Tropical Indo-Pacific from the Red Sea and East Africa to Australia and Hawaii; shallow reefs, sand flats and seagrass to about 20 m
Water
saltwater
Maximum size
60 cm
Temperature
22–26°C
pH
8.1–8.4
Hardness
dKH 8–12, SG 1.023–1.025
Minimum tank
200 litres
Care level
expert
Temperament
peaceful
Reef safe
with_caution

Care

The black sea cucumber, or lollyfish, is a smooth, soft, all-black sea cucumber of shallow Indo-Pacific reef flats, sand flats and seagrass meadows. It is often coated in sand, which camouflages it and may shade it from the sun. It has a ring of 20 black, branched feeding tentacles round the mouth. Most are about 20 cm long, but it can reach 60 cm. Toxin warning: when stressed, injured or dying, sea cucumbers can release toxins (holothurin and related saponins) that can wipe out a tank. This species gives off a toxic red fluid when its skin is rubbed or damaged, and when attacked it can expel its internal organs, which are also toxic to fish. LiveAquaria marks it as poisonous when stressed or when it dies. Keep a good protein skimmer and fresh activated carbon running, guard pump and powerhead intakes so it cannot be sucked in, and remove any dead or dying cucumber at once. Tank set-up: a large, mature tank with a wide, deep sand bed rich in detritus. LiveAquaria advises not overstocking, at about 7.5 cm of animal per 75 litres, so a typical 20 cm animal needs about 200 litres at least. Medium flow suits it. It is very sensitive to copper and high nitrate. Water: about 22–26 °C, pH 8.1–8.4, dKH 8–12 and specific gravity 1.023–1.025. Role: a sand sifter that swallows sediment and digests detritus and organic matter from it, cleaning and turning the sand bed. In a small or young tank it will starve. Copper: copper-based medicines are toxic to shrimp, snails and most invertebrates, and some plant fertilisers carry copper too. Never treat a display tank holding this animal with copper; treat fish in a separate hospital tank, and drip-acclimatise new arrivals slowly. Sources: LiveAquaria (liveaquaria.com/products/sea-cucumber-black-expert-only); Wikipedia (en.wikipedia.org/wiki/Holothuriaatra). Checked October 2026.

Diet

Deposit feeder: sifts sand with its tentacles for detritus, bacteria, microalgae and organic matter. A large, mature sand bed is essential; supplement with sinking fine foods, powdered plankton or sinking pellets scattered on the sand if it shrinks.

Breeding

Sexes cannot be told apart from outside. It spawns mainly in summer and autumn (all year near the equator), releasing eggs and sperm into the water. It also reproduces asexually by splitting: a waist forms and deepens until the animal divides into two shorter cucumbers, mostly in smaller animals. Splitting has occasionally been reported in aquariums, but it is not bred in the hobby.

Compatibility and tank mates

Peaceful and does not harm corals or fish, but reef safe only with caution because of the risk of toxins if it is injured, sucked into a pump or dies. Avoid fish and invertebrates that pick at it, such as puffers, triggers, large angelfish, crabs and bristle-worm-heavy rubble that may damage it.

Last updated 8 October 2026. Community-edited care guide on Aquatic-Auctions.

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