Study finds some fish can add and subtract

Author says study provides example of how humans underestimate some species.

A new study has found cichlids and stingrays can add and subtract in the number range of one to five, can be trained to distinguish between quantities of three and four, and can identify small quantities likely without counting.

A new paper detailing the findings appears in the journal Scientific Reports.

While there is previous literature documenting these animals' ability to "eyeball" quantities, the recent paper is the first to show they are capable of performing calculations.

"We trained the animals to perform simple additions and subtractions," Prof. Dr. Vera Schluessel of the Institute of Zoology at the University of Bonn and the leader of the research group said in a statement.

"In doing so, they had to increase or decrease an initial value by one."

Researchers presented a picture containing colour-coded shapes to cichlids and stingrays, followed by two new ones, with one containing the correct answer. When they swam to the right image, they received a food reward.

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The images shown during the tests combined different shapes, sometimes within the same picture.

"The animals had to recognize the number of objects depicted and at the same time infer the calculation rule from their color," Dr. Schluessel said.

"They had to keep both in working memory when the original picture was exchanged for the two result pictures. And they had to decide on the correct result afterwards. Overall, it's a feat that requires complex thinking skills."

Dr. Schluessel said the results confirm humans tend to underestimate other species, especially those that aren't typically considered "cuddly or cute."


The study's authors were surprised by the findings because fish don't have a neocortex - the part of the brain mammals use to perform complex tasks, like math.

Neither cichlids nor stingrays have demonstrated proficient numerical skills in the wild - and it's not clear why the animals have evolved to have this ability.

Thumbnail: custom by Cheryl Santa Maria. Graphical elements courtesy of Canva.