Invertebrates
Sea Apple
Pseudocolochirus violaceus · also called sea apples
Anchored firmly to a reef outcrop, a sea apple flares its feathery crown of orange tentacles into the current, drawing in drifting plankton one tentacle at a time. Disturb it seriously enough, though, and this vividly coloured animal can release sticky, toxic threads capable of killing nearby fish outright.
Overview
The sea apple, Pseudocolochirus violaceus, is a brightly coloured filter-feeding sea cucumber native to tropical coral reef habitat across the Indo-Pacific region. Its vivid colouration and potent defensive toxin set it apart from most other, duller sea cucumber species.
Beauty with a genuine warning
The same bright colours that make the sea apple a popular aquarium subject also hint at a real defensive capability, one that can turn a stressed sea apple into a serious hazard for any fish sharing its confined space.
Status
Not Evaluated — no formal conservation assessment completed, though wild populations across its broad Indo-Pacific range are thought to remain generally stable.
Sea Apple: common questions
Is the sea apple dangerous to other fish?
When sufficiently stressed or threatened, a sea apple can expel sticky, toxin-coated threads called Cuvierian tubules from its body, a defensive response that can prove genuinely lethal to other fish sharing a small, enclosed space such as an aquarium, making it a risky choice for community reef tanks.
Why is the sea apple so much more colourful than other sea cucumbers?
A sea apple displays notably vivid, saturated colouration, often deep purple or blue with bright orange or red tentacles, a striking appearance that sets it apart from the duller, more camouflaged colouring typical of most other sea cucumber species, though the specific evolutionary reason behind this bold colouration remains debated.
How does a sea apple eat?
A sea apple extends a crown of feathery, branching tentacles into the surrounding water current to capture drifting plankton and organic particles, periodically drawing individual tentacles into its mouth one at a time to consume the trapped food before extending them again.
Where does the sea apple live?
The sea apple is native to tropical coral reef habitat across the Indo-Pacific region, generally found anchored to rock or coral in areas with moderate water flow, which provides a steady supply of the drifting plankton the species relies on for its filter-feeding diet.