Photo: Midshipman fish monitor a nest, which contains embryos secured to the rocks. Credit: Margaret A. Marchaterre Melatonin, the same hormone that helps humans sleep and combat jet lag, teams with circadian rhythm to control the nocturnal mating song of male plainfin midshipman fish, a new study out of Cornell University finds.
The fish (Porichthys notatus), a bit more than a foot long fully grown, sings through the night when it wants to attract a mate, the "song" more akin to a droning hum that can last more than an hour at a stretch. Ranging in the Pacific Ocean from Alaska down to Southern California, the sound used to puzzle seafaring Californians.
Now, though, the sound has long since been identified as the mating song of the male midshipman fish. The question that remained for scientists was what keeps it singing at night.
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To find out, Cornell researchers first tested the possibility that circadian rhythm -- an internal clock -- controlled the night singing. They put midshipman fish in darkness for a full week, without light cues.
The fish still sang generally once per day, suggesting the clock was doing its job keeping the humming on schedule.
Next, the scientists kept the fish in constant light, suppressing melatonin production, which happens in darkness. That setting almost fully stopped the humming.
However, a melatonin substitute brought back the fish's hum, but without any sense of timing -- the songs were randomly sung at varying times of day.
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"Melatonin acts as a 'go' signal for the nocturnal call of the midshipman fish," lead author Ni Feng told the Cornell Chronicle.
While in diurnal (active during the day) creatures such as birds, melatonin brings quiet, it does the opposite in the midshipman fish.
"Our results demonstrate that vocalizations in fish, as in birds, follow a circadian rhythm and are sensitive to melatonin," the Cornell team wrote.
The researchers' findings have been published in the journal Current Biology.
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