Sharp Minds on the Reef: Are There Intelligent Fish?

Exactly what constitutes intelligence in an animal is a controversial subject. It can also be a question that we regard subjectively, comparing the intelligence of an animal directly to our own, even though the animal is likely to have evolved to face very different pressures than us, pressures requiring a very different kind of intelligence. Despite this, it is true to say that long-term memory, teamwork, and tool use are all hallmarks of higher intelligence and, until recently, were considered to be the exclusive reserve of animals such as primates. Remarkably, evidence now exists to show that coral reef fish have long-term memories, work in teams, and even use tools.

How long can fish remember things?

Once a skill or some information has been learned, it needs to be regularly reinforced, otherwise it will be forgotten. The amount of time that a new skill can be remembered is known as a “memory window”. Contrary to common belief, memory windows in fish can be extensive. The simplest test examined how long a fish would remember where a piece of food was hidden. Reef fish can memorize landmarks in their habitat and retain the memory for anything up to six months without it being reinforced. They can also remember other individual fish for considerable periods; experiments suggest that individual recognition can persist between fish that have not encountered each other for more than a month.

Do fish use teamwork?

Teamwork is often considered to be an indication of advanced intelligence because it requires individuals to fulfill roles and to work together in a concerted way. One possible example of this in fish is mobbing behavior, where individuals band together to harass a predator that has moved into the locality. For instance, groups of butterflyfish and surgeonfish are known to mob predatory fish such as moray eels and lizardfish. In doing this, the prey fish can prevent the predator from launching a surprise attack in the first instance and ultimately drive it off. Because the many are stronger than the few, this only works if the fish team up.

How else do reef fishes show intelligence?

Fishes such as the clown cons (Cons aygula) and the redbreast wrasse (Cheihnus fasciatus) pick up urchins in their mouth and crush them by ramming them into the reef. They may repeatedly use the same parts of the reef to do this, possibly in the same way that thrushes use particular “anvil” stones to break apart the snails they feed on. The yellowhead jawfish (Opistognathus aunfrons) constructs its own burrow to amazingly high standards; the entrance must be precisely the right size for the fish to swim into and no larger. The burrow is built out of small stones and each must conform to the fish's exacting standards, making a
perfect fit with the others around it, otherwise it will be rejected.