In the 1980s, houseboats around San Francisco Bay were puzzled by a droning hum that they thought were extraterrestrials that start in the evening and go on in the morning. The culprits are male plainfin midshipman singing to attract mates.
Singing Fish
Named after the bioluminescent organs on its underside, the plainfin midshipman resides in deep water during the fall and winter and move to shallow waters in the spring and early summer. They move to coastal waters between Alaska and Baja California, then the male fish 'sings' to attract potential mates.
This happens exclusively at night controlled by their internal clocks. The hormone that manages this internal clock is the same hormone that regulates bird activity and help humans sleep. Melatonin keeps the fishes from being late to their nightly crooning, it helps regulate internal clocks - way for our bodies to know if it's time to sleep.
"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," Cornell University's Andrew Bass, the paper's senior author, said in a statement. "Our study helps cement melatonin as a timing signal for social communication behaviors."
To understand the melatonin's effect on the fishes' behaviors, they were exposed to constant light for 10 day stretches. Sine the melatonin can only be produced in the pineal gland at the dark, the constant light visibly supressed the humming of the fish. After the fish were given a melatonin substitute, they continued to hum though at random times a day.
"Melatonin acts as a 'go' signal for the nocturnal call of the midshipman fish," said Ni Feng, Ph.D. '16, a former graduate student in Bass' lab who is currently a postdoctoral researcher at Yale, the paper's first author. "Surprisingly, at the single call timescale, constant light also decreased hum duration, but melatonin maintained hum duration at normal levels, a finding also found in diurnal birds."
Watch the fish sing here:
