Some inter-species relationships are what they call ' commensal'. One partner benefits from an aquatic friendship, while its counterpart neither benefits nor harms. The pearlfish, an eel-like fish with an elongated body, resides in the rectum of the sea cucumber, hiding from predators. Sometimes, the selfish (pun intended) pearlfish turns into a parasite and feeds on the gonads of the sea cucumber.
The cleaner shrimp is fond of cleaning by getting rid of dead cells and parasites of symbionts, which are partners in symbiosis. Turtles and large fish queue at cleaning stations, as if they were carwash lanes, for an aquatic cleaning job. The cleaner shrimp also takes up the position of an oral hygienist. Meanwhile, the shrimp benefits from a menu of parasites and dead cells and its symbiont, the client fish, benefits by getting itself cleaned.
The relation between the female anglerfish and so-called ' luminous bacteria' is almost bizarre. The anglerfish has an antenna-like filament on its head, housing luminous bacteria in a bulbous structure perched on top of the filament, like a lighthouse keeper on duty in a lighthouse. The anglerfish rotates its filament-like lights in a lighthouse to attract prey and potential mates.
In gratitude for ‘ lighthouse duties’, the angler fish offers protection and nutrients in return. Peculiar of note is that, allegedly, the bacteria wouldn't even possess luminescent qualities if it hadn't been for the host synthesizing the required chemicals.
The hitchhiking suckerfish, or remora, attaches itself to turtles, manta rays and sharks to travel distances without losing energy. They are aquatic fare dodgers, using their sucker-like organ on top of their heads to stick to their ‘symbionts’ and travel for free.
Another hitchhiking traveller is the emperor shrimp, comfortably supported by more giant nudibranchs, meanwhile feeding for the sea's surface. Cardinalfishes hide between the long venomous spines of sea urchins, benefiting from a universal bond. Predators will think twice before undertaking an attack. Ironically, the cardinalfish is immune to the horrific weapons of the sea urchin.
