>To relieve their pervasive infestations, fish (referred to as clients) frequent patches of reefs manned by small species of fish and shrimp that are specifically adapted for dining on the pests. The behavior, known as cleaning, has long been touted as a classic example of symbiotic mutualism, where two species benefit from a close relationship. A growing library of lab and field experiments published during previous decades has revealed, however, that this once clear-cut example of cooperation is actually rife with conflict and high-stakes drama driven by a single overriding dilemma: Given the choice, cleaners prefer to cheat by taking painful nips of delectable mucus, scales and flesh from clients rather than nibbling crunchy crustacean carapaces. This enticing conundrum has lured scientists deep into the abstract realms of market theory, reciprocal altruism and game theory models, including the much-iterated prisoner's dilemma, in an attempt to better understand the evolutionary origins of cooperation. But most gratifying for divers is that the steady flow of research has begun to unravel the inner workings of a favorite bit of underwater theater.
>Researchers have learned plenty about the gnathiid larvae as well — most surprisingly, at times it takes as little as 30 minutes for the parasites to draw down a gut full of blood before heading home to molt. Such a rapid turnover helps explain why one rabbitfish was documented visiting a cleaning station 144 times during a single day. Most interactions between cleaners and clients last only seconds, while others continue for minutes. To increase their chance of survival during stopovers at cleaning stations, larvae prefer attaching to the blood-rich lining inside a fish's mouth or gills, where they can feed fast. But most pests end up wedged beneath scales or clamped to fin rays in easy reach of hungry mouths.
>In market systems where cleaners and clients have the option of cooperating, cheating or defecting, not everyone is treated the same. Even though cleaners enjoy a semblance of immunity from being eaten, bluestreaks obtain an extra layer of protection by applying tactile stimulation across the backs of predatory clients with flurries of fins. The calming strokes, proven to lower stress by raising a fish's cortisol level has evolved, like intra- and interspecies communication, into an essential tool for balancing social demands such as enticing heavily infested clients to hang around for prolonged inspections.
>The study of bluestreak behavior continues. A recent lab experiment using a classic test of self-awareness determined that the remarkable fish are able to recognize themselves in mirrors — the select domain of only a few animals, including us.
>© Alert Diver — Q1 Winter 2019