Problems with equating thermal preference with ‘emotional fever’ and sentience: comment on ‘Fish can show emotional fever: stress-induced hyperthermia in zebrafish’ by Rey et al. (2015)

Rey et al. [1] report that zebrafish captured with a net and held for 15 min at a water temperature of 27°C exhibited a subsequent preference to swim in water temperatures of 28.75 +/- 0.278C and higher for the next 4 h, compared with controlfish that were neither captured nor held in nets. They report that approximately 25% more net-confined fish resided in areas with water temperatures of 29°C or higher (compared with controls; their fig. 2). Based on these results, they conclude that: (i) net-confined fish exhibit hyperthermia; and(ii) this hyperthermia is caused by psychological stress (e.g. anxiety) which they refer to as ‘emotional fever’ [1, p. 1]. Rey et al. state that ‘ . . . lack of emotional fever in fishes . . . ’ would reflect ‘ . . . a lack of consciousness . . . ’[1, p. 1] and claim that the occurrence of emotional fever in zebrafish ‘ . . .removes a key argument for lack of consciousness in fishes’ [1, p. 1]. Thus, Rey et al. [1] are clearly inferring that their results are consistent with consciousnessin fishes. We contend that the methods, analysis and interpretation of their data are flawed and that their conclusions are, therefore, unfounded.