Study uncovers why a fish species only hums its ‘love song’ at night

WASHINGTON // In one of the marvels of nature, males of a fish species called the plainfin midshipman court females during breeding season with a nocturnal “love song”, creating an otherworldly sound.

Laboratory experiments showed that the vocalisation of the fish, which dwells in Pacific coastal waters, is a low-frequency hum like a foghorn. It is controlled by a light-driven internal clock and melatonin, known to govern sleep and wake cycles, researchers said.

“The production and hearing of vocal signals plays a central role in their social interactions and reproductive behaviour,” said Andrew Bass, a professor of neurobiology and behaviour at Cornell University.

The plainfin midshipman, up to 38 centimetres long, generally has an olive-brown colour.

Its name comes from rows of bioluminescent organs on its underside that reminded early observers of the buttons on a midshipman’s uniform.

Males migrate during the late spring and summer from deep offshore sites into shallow intertidal waters, where they build nests below rocky shelters.

Throughout the night, they produce hums by vibrating a gas-filled bladder within their abdomen to attract females to their nests to spawn. One hum can last about two hours. Neighbouring males often hum together in a chorus.

The study, published in the journal Current Biology, involved wild-caught fish kept in rooms where lighting could be controlled.

In constant darkness, the fish hummed pretty much on schedule, thanks to their internal clock, or circadian rhythm.

In constant brightness, which lowers melatonin production, humming was suppressed. When kept in constant light but given a melatonin-like substitute, they continued to hum, but at random times of the day.

* Reuters