FISH can do maths, scientists have found.
It was thought they might flounder in arithmetic tests — but they showed they could quickly work trout sums between one and five.
They were first trained to recognise that yellow symbols represented adding by one and blues symbols meant subtracting by one.
For example, if they were shown three blue shapes they would find a treat by adding one to three and swimming through a gate displaying four shapes.
They were right between 69 and 94 per cent of the time.
Maths ability has already been found in gorillas, monkeys, dolphins, elephants, birds, salamanders — and even bees and spiders.
The latest tests were carried out on freshwater sting rays at the University of Bonn, in Germany.
Dr Vera Schluessel told journal Scientific Reports: “It could help them recognise individual fish by counting their stripes or spots.”
Next lesson — the decimal plaice?