Goldfish may not have bad memories after all, as they can keep track of how far they have swum.
Scientists trained goldfish to swim 70 centimeters, then stop when someone waved over their tank. When the waving was taken away, the goldfish still remembered to swim almost the exact same distance for a tasty bloodworm snack.
They simply used a stripy pattern on their tank to judge how far they had travelled. They used rocks, algae, and submerged branches in nature.
Researchers worked out the goldfish using the stripes because, when the stripes were placed close together, the fish got confused over the distance.
How did the Scientists train Goldfish?
Scientists created a tank with 2cm-wide black and white vertical stripes along the walls and base.
Nine goldfish were trained to swim along the tank for 70cm, and then return to their starting position when someone waved over them using a food reward.
The researchers then stopped doing the gestures and tested the fish using different backgrounds to see if they could still remember the 70cm swimming distance.
Each fish made the journey 45 times for each background.
Dr. Adelaide Sibeaux, who led the study from the University of Oxford, said:
'Forgetful people say they have a mind like a goldfish, but that's not fair.'
'Goldfish are clearly not stupid at all, as they have a good memory for distance based on the flow of objects passing by as they swim, like stripes on the tanks.'
The goldfishes swam only 47cm on average when the stripes on their tank were switched for stripes closer together, suggesting the fish had used the visual background to work out the distance.
However, goldfish do not use the time of a journey to judge their distance. Time may be a poor strategy for navigation in goldfish because they frequently get delayed either by socialising, mating, or trying to find food.
It's important for a fish to understand distance so they can find a home after a trip or a shelter when being chased by a predator.
This study was published in the journal 'Proceedings of the Royal Society B. Biological Sciences.'
The results suggest that fish can adjust their navigation skills to a wholly different terrestrial environment.
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