This finding, published in Scientific Reports, reveals a previously unknown mathematical capability in these aquatic animals. Led by Prof. Dr. Vera Schluessel from the Institute of Zoology, the study sheds light on the cognitive abilities of fish, challenging assumptions about their intelligence.

Method

The study involved training stingrays and cichlids to perform basic arithmetic operations, such as increasing or decreasing an initial value by one. Using a method similar to that used with bees in previous research, the researchers presented the fish with collections of geometric shapes coloured either blue or yellow to indicate “add one” or “subtract one,” respectively. The fish learned to associate the colours with the corresponding mathematical operations and demonstrated their understanding by consistently choosing the correct answers in subsequent tests.

Cognitive flexibility 

Remarkably, the fish were able to apply this knowledge to new tasks, even when the calculations became more complex. They successfully solved problems involving different shapes and colours, indicating a level of cognitive flexibility previously unrecognized in these species. The researchers were particularly surprised by the fish’s ability to infer the calculation rule from the colour cues and apply it to various scenarios.

No neocortex

This achievement challenges conventional beliefs about fish intelligence, especially considering that neither cichlids nor stingrays possess a neocortex, the brain region typically associated with complex cognitive functions in mammals. Furthermore, the study highlights the importance of recognising and respecting the cognitive abilities of non-mammalian species, which are often underestimated or overlooked.

The study suggests that fish possess more sophisticated mental capacities than previously thought, which has implications for our perception of fish intelligence and raises important questions about their welfare and conservation in the face of commercial fishing practices.