Fish yawn: the state-change hypothesis in juvenile white-spotted char Salvelinus leucomaenis

Abstract

Yawning is a ubiquitous stereotyped action in vertebrates. Yawning may induce behavioral state changes in animals through its arousal function, but no studies have explicitly examined this state-change hypothesis in fish. This study examined the state-change hypothesis in juvenile white-spotted char, Salvelinus leucomaenis. We observed 48 yawns in 23 out of 41 juveniles during 600 s of observation in the laboratory. Thirty-two of these yawns occurred while juveniles were stationary on the substrate, and they were concentrated immediately before the behavioral transition from stationary to active. These results support the state-change hypothesis. Sixteen yawns were observed after the behavioral transition, and their durations were longer than those before the transition. Although we suspected that this prolonged yawning after the transition would be associated with feeding and thermoregulation in the juveniles, we could not determine the cause of this difference. Further studies are needed to understand fish yawning and the origin of animal yawning.