THEY MAKE TOOLS
Tool use is a sign of higher intelligence that various fish have. Archerfish use droplets of water as bullets to shoot insects off vegetation above the water’s surface; they can even adjust the aim to compensate for the way light bends as it passes between air and water, and still hit their target.
A few years ago, researchers in Norway saw captive Atlantic cod inventing a new tool to feed themselves. Three cod, in two separate tanks, accidentally got their identification tags tangled in a string that released food from an automatic feeder. Beforehand, the cod had learned to pull the string with their mouths to get food. But these three cod worked out that it was much faster to deliberately hook their tags on the string then spin around and gobble the food.
Dr Helen Scales is a marine biologist and science writer. Her latest book is Eye Of The Shoal (£16.99, Bloomsbury).