© Todd Anderson/Stanford UniversityTwo male cichlids spar with each other by showing what big mouths they have. When two fish fight, all their movements are at least slightly out of sync. But when the foe is a fish's mirror image, the "opponent's" actions are perfectly in time, which seems to trigger an element of fear.
Fish looking at a mirror showed increased brain activity in regions linked to fear than fish faced with an actual fish separated by glass, the study showed. However, in both instances the fish responded the same physically, engaging in a routine of combative gestures to try to fight the other fish - be it a reflection or an actual opponent.
"It seems like something they don't understand," said Julie Desjardins, researcher and post-doctoral biologist at Stanford University. "I think this stimulus is just so far outside their realm of experience that it results in this somewhat emotional response."
Desjardins and Stanford biologist Russell Fernald arranged 20 minute-long sparring sessions for male African cichlids, a freshwater territorial fish. A clear wall across the middle of the tank kept the combatants apart when two fish were pitted against each other, so there was never any actual fish-to-fish contact. In some instances, the clear wall was replaced with a mirror.
