New Delhi: A cichlid fish species and stingrays can perform mathematical operations, a new study has found. The cichlid fish species, Zebra mbuna, and stingrays, can carry out addition and subtraction. 


The findings of the study were recently published in the journal Scientific Reports. 


According to the authors, the results highlight that the numerical abilities of fish are on par with those of other vertebrate and invertebrate species.


The Fish Recognise Yellow And Blue Colours As Symbols For Mathematical Operations


Zebra mbuna and stingrays can add and subtract one from the numbers one to five, the study said. Professor Vera Schluessel, from the University of Bonn, Germany, who led the study, tested whether eight zebra mbuna (Pseudotropheus zebra) and eight freshwater stingrays (Potamotrygon motoro) could be trained to recognise colour blue as a symbol for addition by a factor of one and the colour yellow as a symbol for subtraction by a factor of one. 


According to the study, cards with either blue or yellow were shown to the fish. Then, they were shown two gates containing cards with different numbers of shapes. One of the cards represented the correct answer.


How Do The Fish Perform Mathematical Operations?


For instance, if a fish was shown a card with three blue shapes, they would add one to three and swim through a gate containing the card with four shapes, the study said. Also, if a fish was shown a card with three yellow shapes, they would subtract one from three and swim through a gate containing the card with two shapes.


The fish which swam through the correct gate were rewarded.


How Good Were The Fish At Their Tasks?


Six individuals of the zebra mbuna species and three of the stingrays learned to consistently associate blue with addition and yellow with subtraction, the study found. It took an average of 28 sessions for zebra mbuna and an average of 68 sessions for stingrays to learn addition and subtraction. 


Fish generally exhibit good performance in these tasks, but find it easier to learn addition compared to subtraction. 


The performance of individual fish varied more between Zebra mbuna and stingrays, the study said.


When marine animals were given the task of addition, zebra mbuna selected the correct answer in 296 out of 381 tests, accounting for 78 per cent of the tests. Meanwhile, stingrays selected the correct answer in 169 out of 180 tests, accounting for 94 per cent of the tests.


Zebra mbuna were correct during 264 out of 381 tests related to subtraction. This accounted for 69 per cent of the tests. Stingrays selected the correct answer in 161 out of 180 tests based on subtraction, accounting for 89 per cent of the tests.


Are Numerical Abilities Important To Fish?


Authors speculate that numerical abilities may not be highly important to either species. The findings, however, suggest that numerical abilities could help both species to recognise individual fish by their appearance. For instance, the species can recognise individual fish by counting stripes or spots on fish bodies.


The authors noted in the study that the findings add to a growing body of evidence indicating that cognitive abilities and sentience of fish need to be revisited.