London: Do fish express emotions like humans when in stress? Yes, says a team of researchers who observed for the first time an increase in body temperature of between two to four degrees in zebrafish when subjected to stressful situations.
This phenomenon, known as emotional fever, is related to the emotions expressed when we are under stress and has been linked to consciousness.
The emotional fever has been observed in mammals, birds and certain reptiles but never in fish till date.
For this reason fish have been regarded as animals without emotions or consciousness.
The experiment with 72 zebrafish has brought this view into question.
"These findings are very interesting as expressing emotional fever suggests for the first time that fish have some degree of consciousness," said Sonia Rey from University of Stirling in Britain and Universitat AutAnoma de Barcelona (UAB) in Barcelona, Spain.
To reach this conclusion, the researchers divided the fish into two groups of 36 and they were placed in a large tank with different interconnected compartments with temperatures ranging from 18 degrees Celsius to 35 degrees Celsius.
The fish in the control group were left undisturbed in the area where the temperature was at the level they prefer: 28 degrees Celsius.
The other group was subjected to a stressful situation when they were confined in a net inside the tank at 27 degrees Celsius for 15 minutes.
The fish subjected to stress tended to move towards the compartments with a higher temperature, increasing their body temperature by two to four degrees.
The researchers point to this as proof that these fish were displaying emotional fever.
Scientists differ on the degree to which fish can have consciousness.
Some researchers argue that they cannot have consciousness as their brain is simple, lacking a cerebral cortex and they have little capacity for learning and memory and have no ability to experience suffering.
Others contest this view, pointing out that despite the small size of the fish brain, detailed analyses have highlighted homologies between some of their brain structures and those seen in other vertebrates, such as the hippocampus (linked to learning and spatial memory) and the amygdala (linked to emotions) of mammals.
The research was published in the journal Proceedings of the Royal Society of London, Biological Sciences.