German researchers reveal fish sleep in four distinct stages with complex neural patterns

In the quiet transparency of a zebrafish's body, German scientists at the Max Planck Institute have found a mirror of our own sleeping minds. By tracking eye movements and brain activity in fish that have no eyelids to close, researchers identified four distinct sleep stages — including a deep daytime torpor — that echo the sleep architecture of mammals and birds despite hundreds of millions of years of separate evolution. The discovery suggests that sleep is not a privilege of complex brains, but an ancient inheritance, woven into the biology of vertebrates long before the first creature craw