Researchers from the Universitat Autònoma de Barcelona, together with scientists from the universities of Stirling and Bristol, have observed an increase in body temperature in zebrafish when subjected to stressful situations. This phenomenon is known as emotional fever, as it is related to the emotions that animals feel in the face of an external stimuli and it has even been linked to consciousness.
Until now emotional fever had been observed in mammals, birds and certain reptiles, but never in fish. For this reason fish have been regarded as animals without emotions or consciousness. The experiment, with 72 zebrafish, has brought this into question.
The researchers divided the fish into two groups of 36. The fish were placed in a large tank with different interconnected compartments with temperatures ranging from 18ºC to 35ºC. The fish in the control group were left undisturbed in the area where the temperature was at the level they prefer, 28ºC. The other group was subjected to a stressful situation. They were confined in a net inside the tank at 27ºC for 15 minutes. After this period the group was released. While the control fish mainly stayed in the compartments at around 28ºC, 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 they lack a cerebral cortex. Additionally, they have little capacity for learning and memory; 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.
Researcher Sonia Rey comments “these findings are very interesting: expressing emotional fever suggests for the first time that fish have some degree of consciousness”.
The research was published recently in Proceedings of the Royal Society of London, Biological Sciences. The study began three years ago at the UAB’s Institute of Biomedicine and Biotechnology and was concluded at Stirling University.
Funding: This work was funded by the Swiss National Science Foundation, the NCCR-Synapsy, and EPFL.
Source: Sonia Rey Planellas – UAB
Image Credit: The image is credited to Azul
Original Research: Full open access research for “Fish can show emotional fever: stress-induced hyperthermia in zebrafish” by Sonia Rey, Felicity A. Huntingford, Sebastian Boltaña, Reynaldo Vargas, Toby G. Knowles, and Simon Mackenzie in The Royal Society: Proceedings B. Published online November 25 2015 doi:10.1098/rspb.2015.2266
Abstract
Fish can show emotional fever: stress-induced hyperthermia in zebrafish
Whether fishes are sentient beings remains an unresolved and controversial question. Among characteristics thought to reflect a low level of sentience in fishes is an inability to show stress-induced hyperthermia (SIH), a transient rise in body temperature shown in response to a variety of stressors. This is a real fever response, so is often referred to as ‘emotional fever’. It has been suggested that the capacity for emotional fever evolved only in amniotes (mammals, birds and reptiles), in association with the evolution of consciousness in these groups. According to this view, lack of emotional fever in fishes reflects a lack of consciousness. We report here on a study in which six zebrafish groups with access to a temperature gradient were either left as undisturbed controls or subjected to a short period of confinement. The results were striking: compared to controls, stressed zebrafish spent significantly more time at higher temperatures, achieving an estimated rise in body temperature of about 2–4°C. Thus, zebrafish clearly have the capacity to show emotional fever. While the link between emotion and consciousness is still debated, this finding removes a key argument for lack of consciousness in fishes.
“Fish can show emotional fever: stress-induced hyperthermia in zebrafish” by Sonia Rey, Felicity A. Huntingford, Sebastian Boltaña, Reynaldo Vargas, Toby G. Knowles, and Simon Mackenzie in The Royal Society: Proceedings B. Published online November 25 2015 doi:10.1098/rspb.2015.2266
