Activity levels and daytime sleepiness can be combined into a ‘behavioural clock’ that predicts whether a fish will have a short life or a long one.

You’re staring at your aquarium. It’s late. Everything is quiet. And there’s your fish, floating calmly, fins moving slowly, eyes wide open. Are they... asleep? Or just zoning out? Fish don’t come ...

A new study analyzed the sleep patterns of jellyfish and sea anemones and found they share some sleep traits with humans. The research could provide insight into the origins and function of sleep.