A new study has said that fish can detect fear in other fish, and then become afraid too, suggesting that animals too can have complex emotional lives like humans. The research has been conducted on zebrafish, a freshwater fish native to South Asia, and published in the journal Science. It said that fear is contagious for zebrafish and the hormone oxytocin is responsible for the fright catching on. It is same brain chemical that underlies the capacity for empathy in humans.
The study further said that if oxytocin is removed from the equation, the recognition of fear and subsequent reaction mostly go away.
"The apparent concordance between mammals and fish of how oxytocin regulates empathetic behaviour raises the intriguing possibility that the mechanisms underlying empathy and some forms of emotional contagion may have been conserved since fish and mammals last shared a common ancestor," Ross DeAngelis, a postdoctoral researcher at University of Texas said about the study.
The researchers also found that the brain region responsible for regulating fish fear contagion is comparable in some ways to the emotional centre of the mammalian brain.
The study is being considered important as it suggest that empathy may have a longer evolutionary history than previously thought - going beyond the 375 million years ago when the scientists say the last common ancestor between fish and humans existed.
For the experiment, the scientists divided zebrafish into different groups. In one of the experiments, they kept a group of zebrafish in one tank and a single fish in another. Then, they put a substance known to trigger fear (like erratic swimming) in the tank with multiple fish. The researchers saw that the single fish froze as if afraid when its saw their peers reacting through two layers of glass.
However, when they repeated the experiment with genetically modified fish, the percentage of single fish responding to fear went down by half. They then gave a dose of oxytocin to these fish and saw their response changed.