A recent study published in The Proceedings of the Royal Society B has found that fish are able to display emotion, ruling out the widely held belief that they are not sentient creatures. Researchers discovered that zebrafish showed signs of stress-induced hyperthermia, or a rise in body temperature, when exposed to a number of stressors. This response is referred to as “emotional fever,” the capacity for which was thought to have evolved only in mammals, birds, and reptiles. The experiment included placing six groups of fish into tanks with different temperature-regulated chambers, allowing the fish to acclimate to the water, using nets to confine three of the groups to induce stress, and finally releasing the fish to examine their behavior. “The results were striking,” the report stated. Stressed zebrafish spent more time at higher temperatures, resulting in a 2–4 degrees Celsius rise in body temperature. “While the link between emotion and consciousness is still debated,” the report continued, “this finding removes a key argument for lack of consciousness in fishes.”

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