Researchers brought midshipman fish into their lab to work out why they sang at night, reports the BBC.

The researchers found the singing was controlled by a hormone that helps humans to sleep – melatonin.

And looking more closely at how melatonin acts on receptors in different parts of the fish’s brain could help explain why it is such a powerful “chemical clock” with a role in the timing of sleep-wake cycles, reproduction and birdsong.