Fish may show 'emotional fever', a slight increase in body temperature in situations of stress linked to the emotions and consciousness, a new study suggests.
Researchers from the University of Barcelona in Spain, and universities of Stirling and Bristol in UK, have for the first time observed an increase in body temperature of between two and four degrees in zebrafish, when these are subjected to stressful situations.
This phenomenon, known as emotional fever, is related to what animals feel in the face of an external stimulus. Until now emotional fever had been observed in mammals, birds and certain reptiles, but never in fish.
Researchers divided 72 zebrafish into two groups of 36 and placed them in a large tank with different interconnected compartments that had 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 - they were confined in a net inside the tank at 27 degrees Celsius for 15 minutes. After this period the group was released.
While the control fish mainly stayed in the compartments at around 28 degrees Celsius, 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 evidence that these fish were displaying emotional fever.
"These findings are very interesting - expressing emotional fever suggests for the first time that fish have some degree of consciousness," said Sonia Rey from University of Barcelona.
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, a very simple behavioural repertoire and no ability to experience suffering.
Others contest this view, pointing out that, despite the small size of the fish brain, detailed morphological and behavioural 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 findings were published in the journal Proceedings of the Royal Society of London, Biological Sciences.
