Posted by: letsharkslive | January 23, 2010

In case there was any doubt…

It wasn’t until diving became generally accessible as a sport that we were able to see fish pursuing their affairs in their own environment. Until then, when we thought of fish, it was usually of their appearance in the fish-market or an aquarium.

But when diving among them, and seeing what they do, its impossible to fit them into the old stereotype of cold, low, senseless animals.

Much has been learned about the intelligence and cognitive (thinking) abilities of fish, and surprising as it may seem, the only cognitive ability that has been demonstrated by primates and not by fish is the ability to imitate.* Their brains grow neurons throughout their lives, and do so more quickly in a stimulating environment, showing the link between the animal’s experience and its neural development. The development of different parts of the brain has also been linked to different cognitive abilities in different species.

Recognition of others as individuals has long been established in many varieties of fish, both visually and acoustically. The ability is necessary for complex social lives, in which cognition is most evident. I have documented relationships among reef sharks for years. They, too, relate to each other individually.

Social learning is illustrated by the migrations of the surgeon fish, Acathurus Nigrofuscus, described in detail by Arthur A. Myrberg Jr. in 1998. These fish leave their territories all over the lagoon, and travel in single file through paths in the coral to their traditional spawning grounds. They go and return along the same paths each night at precisely the same time, as I have witnessed year after year in the local lagoon. The spawning ground is the only place along the lagoon’s border where the out-flowing current is balanced by the incoming surge, so that the huge cloud of spawn left in the gathering night, stays in place. These short term migrations are the result of social learning. Each generation of fish learns from its elders where to go to spawn, and when.

Triggerfish, Balistidae. often feed on sea urchins. They try to ‘blow’ them over to get access to their undersides. Hans Fricke observed at Eilat how five different individuals of Balistapus undulatus successfully hunted sea urchins by first biting off the spines, which allowed them to grab the urchin and take it to the surface. Then they fed on the unprotected parts beneath, while the urchin slowly sank. In spite of decades of observations, Fricke never saw these triggerfish demonstrate this behaviour anywhere else. It appeared to be the result of social learning.

Intertidal gobies, Gobius soporator, live in tide pools, and during low tide they jump from one to another, without being able to see the target pool at the beginning of their leap. Experimentation showed that the fish had memorized the lay of the land around the home pool by swimming over the region when the tide was in, and were referring to a three dimensional memory to navigate when the outgoing tide left them in a labyrinth of separated pools.

With the exception of humans, fish are more skilful than primates at nest building. At least nine thousand fish species build some sort of nest, either for egg laying or protection.

The male minnow, Exoglossum, selects more than three hundred stones, all of the same size, from as far as five meters away, to build a spawning mound thirty-five centimeters wide and ten high. Others build dome-shaped nests from as many as ten thousand pebbles.

The jawfish, Opistognathus aurifrons, collects stones of various sizes to build a wall, leaving a hole just big enough to pass through. This involves repeated rearrangement of the stones. In between, the fish searches for new stones that might better fit the available space than the ones it has already collected, using flexible behaviour depending on the circumstances. It must be holding a mental representation of the size and shape of stone it requires while searching.

Remarkable flexibility in building, is shown by the ten-spined stickleback Pygosteus pungitius. While the female usually lays her eggs in a nest built by the male, he can build his nest around the eggs if she has already laid them. Great care is required, and a different technique has to be used to avoid damaging the eggs. Since those eggs do hatch, the males achieve their goal.

Redouan Bshary described seeing cooperative hunting between red sea coral groupers (Plectropomus pessuliferus), or lunartail groupers (variola louti), and giant moray eels (Gymnothorax javanicus):

“These two large species of groupers were observed regularly approaching the eels that were resting in a coral cave, and shaking their bodies in exaggerated movements, usually at less than one meter distance to the moray eel. In seven of fourteen observations, the moray eel left its cave and the two predators would swim next to each other, searching for prey. The groupers would often come so close that the two predators touched each other at their sides. While the moray eels sneaked through holes, the groupers waited above the corals for escaping fish.”

Another unusual form of cooperation among different species is exemplified by cleaning symbiosis. Cleaner fish come from many different fish families, and depend on cleaning for their diet to varying degrees. They clean the dead skin and ectoparasites from their clients in return for a meal. Full time cleaners can have about two thousand three hundred interactions per day with clients belonging to one hundred different species.

Cleaners have their client species categorized into two groups: those who only come to their local cleaner, and those whose home ranges include the territories of other cleaners. For the latter, they have competition, so give them priority over the locals.

Cleaners sometimes ‘cheat’ by feeding off the client’s healthy flesh. The clients with no choice of cleaner punish him by aggressively chasing him, and inflicting a bite or two, as they see fit. But these clients benefit in the future, because the cleaner fish give them, but not others who visit in the meantime, a better-than-average cleaning service on the next visit! Cleaners can distinguish more than one hundred individual clients of different species.

Cleaners will hover above the client and touch him with their fins, to influence his decision to come for a cleaning. This touching tactic is also used to try to reconcile with a client whom they have cheated. Cleaners even exploit the presence of a third party in an attempt to make aggressive clients stop chasing them by going to a nearby predator and caressing him, so that the client dares not continue the chase.

Cleaners behave well toward their clients while being watched by potential new ones—but only those who could visit another cleaning station. The sight of a client being treated very well by the cleaner, is more likely to convince the newcomer to come for servicing than seeing him being chased or eaten. This tactic suggests a short term image, or social prestige, that determines a cleaner’s success in attracting new clients.

Such complex social behaviour—cheating, reconciliation, altruism, species recognition, individual recognition, punishment, social prestige, and bookkeeping, is considered to indicate consciousness when displayed in primates.

A similar example of social judgement is given by the practise of predator inspection, in which different individuals take turns to lead others away from the school to look over a predator. Uncooperative fish will not be trusted by their partners in the future. The fish evaluates the behaviour of another individual, remembers it, and takes it into account in future decisions.

Fish and sharks indicate awareness of whether they are visible to a potential prey or predator or not. Certain territorial fish will bite an intruding swimmer only when his eyes are above the surface; when the person looks at them, they retreat.

Shy sharks approach me from behind while familiar sharks always approach my face, when they come, upon my arrival underwater, indicating awareness of being seen by me. The tendency of a shark to pass just within visible range, then back into the veiling light, especially when the shark has been following, beyond visual range, provides further evidence that they are aware of whether or not they are visible.

Reef sharks such as lemon sharks Negaprion acutidens, reef blackfin sharks Carcharhinus melanopterus, and reef white-tip sharks Triaenodon obesus, in my experience, seem to habitually use the curtain of visibility in order to remain hidden while waiting for an opportunistic moment to approach. To this degree, they show that they are aware of being present and observable.

All animals are self-serving entities, seeking food for the self, protecting the self, saving the self, and so forth, so it is logical that they are aware themselves as distinct from others and the environment; survival benefits have favoured self awareness.

An avian veterinarian, Dr. Ross Perry, in Australia, wrote me the following story: “I have befriended a wild Eastern Blue Groper, Achoerodus viridis, that has a passion for sea urchins, the big ones with long sharp dark purplish red spines. She is very selective in how she approaches the sea urchin before striking it repeatedly to crack it open and suck out the contents. Gropers have big fleshy lips and tiny teeth. She prefers me to uncover the underside of the urchin and to hold as many spines back out of the way as is practical before striking. Even so a large spine broke off in her lip that fortunately left enough sticking out for me to cuddle her on her return so I could grasp the spine with finger and thumb and pull it out. This relationship has transformed my thinking about fish as sentient beings.”

Ila France Porcher © 2009

*This and most of the examples of fish cognition are from the review article: Bshary R, Wickler W, Fricke H (2002) Fish cognition: a primate’s eye view. Animal Cognition (2002) 5 : 1-13

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