Fish are also math savvy

published on Thursday, March 31, 2022 at 6:01 p.m.

The circle of animals strong in math is widening: after primates, bees and birds, freshwater fish have shown elaborate numerical abilities up to calculation, according to a study published Thursday.

The ability to perceive quantities has been demonstrated in all vertebrates, and even some invertebrates. They are vital when it comes to searching for food, avoiding predators, choosing a mate or moving in groups.

But ethologists wonder about the way in which this numerical differentiation takes place: simple estimation based on size or finer capacity to count? Studies have revealed that certain monkeys, parrots, pigeons, spiders and bees were able to process isolated numerical information, going as far as solving simple operations.

An experiment carried out at the Zoological Institute of the University of Bonn (Germany), described in the journal Scientific Reports, reveals that fish also have this gift for arithmetic: the zebra mbuna (“pseudotropheus zebra” , a striped cichlid) and the stingray (“potamotrygon motoro”), two freshwater species.

Eight individuals of each species were subjected to several hundred tests, performed in large tanks specifically designed to observe their performance. They were trained there to recognize the color blue as a symbol of addition and the color yellow as a symbol of subtraction, by a factor of one.

They were presented with cards with a number of blue or yellow shapes, then two sliding doors each flanked by a card with another number of shapes – and only one of which was the correct answer.

For example, a fish was shown a card with three blue shapes, and had to calculate that since it was an addition, it should swim to the door associated with a card with four blue shapes. Conversely, if they were presented with a card with four yellow shapes, they had to go to the door associated with a card with one less shape.

If the fish passed through the right gate, they were rewarded: pellets for the mbuna, worms and small shrimp for the rays. Result: Six of the mbuna and four of the stripes managed to consistently associate blue with addition (+1) and yellow with subtraction (-1).

The exercise took a little longer for the mbuna than for the rays, and for both species, the addition was easier to remember than the subtraction, the study says.

This work reveals new cognitive abilities in fish, conclude the authors. They could help the two species recognize their conspecifics by their appearance, for example by counting the stripes or spots on their bodies, they suggest.


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