© AdobeStock
A recent study shakes up some preconceived ideas about animal intelligence. Researchers have shown that a reef fish was capable of passing a cognitive test long thought to be accessible only to great apes. A discovery that calls into question the way scientists assess intellectual abilities in animals.
An iconic test of animal cognition
The test in question is known as the “marshmallow” test, which has been used for several decades to measure an individual’s ability to delay a reward. The principle is simple. The animal may consume a small reward immediately or wait some time to obtain a larger one. This type of test notably assesses self-control and the ability to anticipate future benefit. Until now, this form of cognitive control had mainly been observed in certain great apes, corvids or marine mammals, species known for their advanced intellectual capacities.
In this new study, scientists looked at a cleaner fish living on coral reefs, known for its complex interactions with other marine species. In the experiment, the researchers offered the fish two food options. One was immediately accessible but less interesting, while the other became available after a short delay and offered a greater reward. The results showed that several individuals were capable of voluntarily waiting for the best reward, demonstrating a capacity for cognitive control comparable to that observed in certain species known to be more intelligent.
A strategy already used in nature
For researchers, this result is not entirely surprising when we observe the natural behavior of these fish on reefs. Cleaner fish actually have a special relationship with other fish. They feed on parasites present on the skin of their “clients”, but sometimes must resist the temptation to eat the protective mucus, a more attractive food but which could scare away their partners. In this context, the ability to delay reward could be a skill developed naturally through evolution to maintain these beneficial relationships.
A discovery that broadens understanding of animal intelligence
This study highlights that certain cognitive abilities are not reserved for animals with large brains. Fish have much smaller brains than mammals or birds, but they can still develop complex behavioral strategies adapted to their environment. For scientists, these results invite us to rethink the way in which intelligence is evaluated in the animal world, and remind us that marine ecosystems still harbor many unknown behavioral capacities.
