Do fish really possess higher cognitive powers?

Do fish really possess higher cognitive powers?

Posted in:

In this magazine, we have frequently pondered the intelligence, sentience and self-awareness of the creatures we encounter on our ventures into the aquatic environment and reported on various scientific findings and philosophical discussion held in that regard (see references at the end).

A cleaner wrasse interacts with its reflection in a mirror. A study, which suggests that fish might possess far higher cognitive powers than previously thought, has ignited an intense debate over how we assess the intelligence of animals

Mirror self-recognition test

The standard method for testing whether an animal is self-aware is placing a mark on its body that cannot be viewed directly and then letting it have a look in a mirror. If the animal responds to its reflection and attempts to remove the mark it is considered evidence that the animal is self-aware.

A new study, just published in PLOS Biology, argues that the cleaner wrasse, Labroides dimidiatus, shows behavioural responses that can be interpreted as passing the mark (or mirror) test. But the researchers also pose a question in the title of the paper: “If a fish can pass the mark test, what are the implications for consciousness and self-awareness testing in animals?”

The fish passed the test

The researchers observed that fish attempted to remove the marks by scraping their bodies on hard surfaces after viewing themselves in the mirror. Fish never attempted to remove transparent marks in the presence of a mirror, or coloured marks when no mirror was present—suggesting that marked fish were responding to the visual cue of seeing the mark on themselves in the mirror. In other words, the cleaner wrasse fulfilled the prevailing criterion for being considered self-aware.

The authors then go on to ask whether these behaviours should be taken as evidence that fish are self-aware or whether the test itself needs to be revised. Given that the mark and mirror test was designed for primates and relies on hand gestures towards the marked region as well as changes in facial expression, the researchers also raised the reasonable question of whether it is even possible to interpret the behaviour of divergent taxonomic groups such as fish. Animals that cannot directly touch the marks used in mirror self-recognition tests may therefore be inherently difficult to test regardless of their cognitive abilities.

Healthy debate

We find the debate healthy on so many levels. Firstly, it is always a part of a sound scientific discourse to evaluate both the premise and the findings in a bigger context. That is how we continually move on to higher truths, such as the Earth circling the sun and not the other way round.

As humans, we may also ponder what makes us human and what sets us apart from other living beings, and what we may have in common. As divers, we can only benefit from a better understanding of how and why other creatures we may encounter on our endeavours underwater react the way they do. Haven't we all wondered at some point what may go on in the mind of the animal looking back at us?

PLOS Biology