[Watch this weird little fish walk up waterfalls]The noise comes from male suitors of the species Porichthys notatus, commonly called the plainfin midshipman fish. In animals that sleep at night — as humans do — melatonin is thought to help regulate the internal "clocks" that tell our bodies it's time for some shut-eye. Nocturnal animals also make melatonin when plunged into a dark night, so it clearly doesn't put them to sleep. In midshipman fish, it seems to prompt males to start singing — which is what makes them midnight crooners. Then researchers gave fish drenched in sunlight an artificial melatonin boost, and their not-so-sweet melodies began in earnest — though at random intervals.

Source: Washington Post September 23, 2016 18:22 UTC