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Injuries happen.

Whether you’re a clumsy human or a lucky animal who has narrowly escaped the clutches of a predator, surface abraisions and wounds are common.

When surface maladies occur, it is vitally important for all animals to treat them in order to avoid infection.

For humans in the western world, this is fairly easy to do. The use of sterile equipment, antibiotics, antiparasitic, and antifungal medications, and the ability to care for injuries without the treat of predation gives us ample opportunity to heal.

Such luxuries aren’t available to the other 98 per cent or so of organisms with whom we share this planet. Animals must rely on natural remedies and their own physiological power in order to heal themselves from wounds and to avoid invasion by the opportunists who are actively seeking a place to fester.

The Strategy of Tropical Reef-Dwelling Fish

Tropical fish living in coral reef environments have an effective strategy when it comes to caring for wounds and dealing with ectoparasitic infections: the cleaning station.

Some types of fish and invertebrates perform a cleaning procedure on other kinds of fish, not entirely unlike the treatment we receive at a medical clinic to clean and care for a wound. Client fish (the ones to be cleaned) assume a specific posture at a cleaning station (an area of a coral reef known to be frequented by cleaning fish) in order to solicit a service.

Clients have been documented to do this up to 144 times a day, making it clear that such interactions are common in the coral reef environment.

This setup is viewed as mutualistic, with the clients benefitting from the cleaning and the cleaners benefitting from a free meal.

Photo via Adobe Stock

Blue Tangs (Acanthurus coeruleus) in the Caribbean experience a high frequency of minor surface abraisions from brushes with sea urchins, hard corals, and larger predators.

However, such injuries have a low probability of becoming infected and resulting in further detriment to the health of the fish.

How do they heal so effectively without becoming infected?

Cleaner fish bite at the periphery of the wounds and at dangling muscle fibres, effectively cleaning off any necrotic or infected tissue (one fish’s rotting tissue is another one’s meal).

Healing of injuries is rapid and complete, with a high rate of recovery for all wounded fish, including those with severe abrasions. Individuals with significant surface damage have been documented to spend much more time at cleaner stations when their wounds were fresh (25.4 minutes per hour) than when they had healed over (1.6 minutes per hour).

Treating Ectoparasites

Cleaning stations also provide a medical reprieve for fish that are heavily infected with ectoparasites, a common occurrence in the aquatic world. The attending cleaners selectively prey on the ectoparasites plaguing their clients, as opposed to simply grazing on their surfaces at random. 

When large surgeonfish (Ctenochaetus striatus) in Australia’s Great Barrier Reef were experimentally traumatized with an ectoparasitic isopod on one side of their bodies so that they sustained high rates of infection on that side and no infection on the other, cleaners spent more time working on the infected sides of the fish.

Photo via Adobe Stock

The active removal of parasites and the time spent on heavily infected areas indicate that this kind of medical treatment has an intended purpose for both the client and the cleaner.

In another experimental manipulation, the cleaning process was disrupted by holding client wrasse (Hemigymnus melapterus) in large cages without access to their attendants. Individual wrasse in the cages carried a four-fold higher parasite load than those that had access to cleaning servicesk indicating a strong disadvantage to the clients without access to medical intervention.

Photo via Adobe Stock

These examples demonstrate that the active removal of parasites is an extremely important component of cleaning sybioses, moving far beyond the simplicity of animals picking food off of one another.

Reef-dwelling fish have developed effective ways in which to treat surface wounds and infections. The solution: keep it clean!

This post is an adapted excerpt from my book “The Nature of Human Nature