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Pearlfish (Carapus acus)

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description Pearlfish (Carapus acus) Overview

The pearlfish (Carapus acus) is a slender, translucent fish belonging to the family Carapidae, found in the eastern Atlantic Ocean and Mediterranean Sea. It is notable for its commensal and sometimes parasitic relationship with holothurians (sea cucumbers), into whose cloacal cavity it enters tail-first to shelter during the day, emerging at night to feed on small crustaceans. Adults spawn pelagically, and the larvae pass through a complex developmental sequence before seeking a host.

help Pearlfish (Carapus acus) FAQ

What is the most unusual behavioral trait of the pearlfish?

The pearlfish is notable for its commensal and sometimes parasitic relationship with sea cucumbers (holothurians). It actually lives inside the cloacal cavity of the sea cucumber for protection against predators.

How does the pearlfish enter the body of a sea cucumber?

The slender, translucent fish typically waits until the sea cucumber opens its cloaca to breathe or expel waste. It then slides itself tail-first into the opening, seeking shelter inside the host's body cavity.

Where is the pearlfish Carapus acus typically found?

The species Carapus acus is found in the eastern Atlantic Ocean and the Mediterranean Sea. They generally inhabit shallow coastal waters where sea cucumbers are abundant on the sea floor.

Does the pearlfish harm the sea cucumber it lives inside?

In many cases, the pearlfish merely uses the sea cucumber for shelter and leaves to feed at night, acting as a commensal. However, some pearlfish will feed on the sea cucumber's gonads or other internal tissues, making the relationship parasitic.

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