Fact: There are fish that sing. At San Francisco Bay, residents living in houseboats were mesmerized by a strange hum that starts when darkness fall and stops abruptly before the sunrise.

The Washington Post published an article that the strange noise comes from male suitors of the species Porichthys Notatus, or the ugly fins midshipman fish. On the other hand, the female midshipman only grunts when showing aggression for the male, when it is trying to mate with them. What makes these noises are their swim bladders that seem like a chorus of kazoos, a formation of a flying fish or a swarm of droning bees.

"They certainly sound like an orchestra full or mournful, rasping oboes," SFGate reported in 2004.

Or should one say that their noise is similar to singing mermaids?   

Recently, researchers found out a possible reason why these midshipman fish are singing at night; it's because of a hormone called melatonin. Produced by many plants and animals, melatonin is triggered once darkness sets. However, for animals that sleep at night, just like humans, melatonin secretion is thought to help regulate the internal or body clocks. That explains why some people find melatonin supplements as the cure for insomnia.

Andrew Bass from Cornell University said in his statement in Caltech, "Our results, together with those of others that also show melatonin's actions on vastly different timescales, highlight the ability of hormones, in general, to regulate the output of neural networks in the brain to control distinct components of behavior."

Bass also added that "In the case of melatonin, one hormone can exert similar or different effects in diurnal vs. nocturnal species depending on the timescale of action, from day-night rhythms to the duration of single cells."

In their research to trace melatonin's role in the humming mystery, scientists tested the singing cycles of these midshipman fish in darkness and light and found out that when there is light, they never sang at all. So, the researchers gave melatonin to the fish while they are in sunlight, and finally, they heard the not-so-sweet melodies of these fish.