Fish can show emotional fever: Stress-induced hyperthermia in zebrafish

Sonia Rey, Felicity A. Huntingford, Sebastian Boltaña, Reynaldo Vargas, Toby G. Knowles, Simon Mackenzie

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48 Citations (Scopus)


© 2015 The Author(s) Published by the Royal Society. All rights reserved. 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.
Original languageEnglish
Article number20152266
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1819
Publication statusPublished - 25 Nov 2015


  • Consciousness
  • Emotional fever
  • Fish sentience
  • Fish welfare
  • Stress-induced hyperthermia
  • Zebrafish


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