New research has removed a significant obstacle to the theory that fish are conscious, emotional creatures. A key argument against fish sentience is that, unlike mammals, birds and even some reptiles, they do not seem to respond to stressful situations with an ’emotional fever’ – an increase in body temperature that serves as a kind of physiological rolling-up of sleeves.

But new experiments suggest that stressed zebrafish seek out water that is warmer than they usually prefer, which gives the same result. The scientists conclude that fish are “behaviourally complex animals that may well be sentient and conscious to an extent”.