Fish: Fearful of Mirrored Reflections
"It seems like something they don't understand," said Julie Desjardins, lead author of the paper describing the study. "I think this stimulus is just so far outside their realm of experience that it results in this somewhat emotional response."
Desjardins and co-author Russell Fernald arrived at their conclusion by comparing the behaviour and brain activity of male African cichlid fish during and after one-on-one encounters with either a mirror or other another male of about the same size.
The territorial male cichlids usually react to another male by fighting in a sort of tit-for-tat manner. Desjardins suspects the fish fighting their own reflections become fearful because their enemy in the mirror doesn't exhibit the usual reactions they would expect from another fish.
"In normal fights, they bite at each other, one after the other, and will do all kinds of movements and posturing, but it is always slightly off or even alternating in timing," Desjardins said. "But when you are fighting with a mirror, your opponent is perfectly in time. So the subject fish really is not seeing any sort of reciprocal response from their opponent."
The discovery that fish can discern a difference so subtle could prompt researchers to take a second look at how well other lower invertebrates can discriminate among various situations.
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