There are a few species of pearlfish, but they share some characteristics. They are small creatures. They have thin, eel-like bodies. They lack scales, and are often translucent. And most of them like to have invertebrate neighbors.
Pearlfish, being easy prey for other fish, have developed a habit of “moving in” with invertebrate animals, hiding within their shells for protection from predators. It’s a trait which has garnered notice within the ichthyology community, mostly due to their relationship with one invertebrate in particular.
While they may hide commensally in a clamshell or alongside a starfish, they’ve achieved a level of fame for their connections with sea cucumbers. This is because they like to live inside of sea cucumbers, which are considered unpleasant by predators. Specifically, the like to live inside the anus of sea cucumbers.
Not just one, either; a single sea cucumber may host multiple pearlfish, which can live most of their lives inside and even mate with other pearlfish while lodged in the sea cucumber. They can draw nourishment from the discharge of the larger creature, as well, and they don’t interfere with its eating (which takes place on at the sea cucumber’s mouth) or breathing (which unfortunately does take place around the anus, but does not use the chamber inhabited by the pearlfish).
The fish isn’t the only creature to seek protection inside of sea cucumbers… tiny crabs and worms have also been known to do so… but it is the largest of them, and the most famous; this is probably due to the fact that the fish have been repeatedly filmed entering their targeted orifice.
Unfortunately, the commensal (there’s that word again… it’s a biology term referring to a relationship in which one animal gains and another animal neither gains nor loses anything) arrangement pearlfish share with other invertebrates doesn’t always extend to the sea cucumber. Despite being the best pairing for the fish, they sometimes get greedy and take more than simple shelter from the sea cucumber; they have also been known to feed on the bottom-dweller’s internal organs, particularly its reproductive system.
So, there’s a bit of information for the night… a misshapen, mindless thing that has multiple creatures with heads lodged firmly in its ass, and not a word of politics.
Question of the night: Have you ever kept, or considered keeping, a fish tank?
