Males of the plainfin midshipman fish court females while singing to them at nights. Their nocturnal love song has been a mystery since 1980, but scientists finally discovered in 2016 what makes this species sings only at night.
The study was published Thursday in the journal Current Biology and explains that the fish biological clock is the one behind the night singing of the plainfin midshipman mystery.
Scientist kept a group of midshipman fish in constant light to prove that an internal clock controls the night humming of the species. They put the fish under constant light and researchers noticed the fish almost completely suppressed their singing.
But when plainfin midshipman fish were in constant darkness, the species hummed almost on a schedule. Scientist discovered that the fish vocalization is controlled by an internal clock that is stimulated by light and the hormone melatonin.
Melatonin is known to govern sleep and wake cycles in almost all creatures, including humans. Melatonin is the hormone that keeps birds quiet at night and has a reverse effect on the midshipman fish.
The hormone activates at night and provokes that the midshipman gas-filled bladder starts vibrating to produced the love hums to attract females. Males migrate during late spring and summer from deep sites located offshore into shallow intertidal waters, the study says. Once there, the midshipman builds its nest beneath rocky shelters and sing to find a mate.
The study discovered that when plainfin midshipman fish are in the constant light, the condition lowers their melatonin production. But if they are giving melatonin-like substitutes, they continue to hum, though at random times.
Professor Andrew Bass led the research said melatonin worked as a ‘go’ signal for the species to sing at night. Dr. Ni Feng from Yale University, who was also involved in the research, elaborated on how the melatonin worked on the midshipman and stated the hormone serves to wake the fish up and start singing to courtship females.
Dr. Feng thinks this study could pave the way to study hormones and reproductive-related vocal communication behaviors shared by “many vertebrate species.”
Getting to know the plainfin midshipman fish
The plainfin midshipman can be as big as 15 inches (38 centimeters) long and generally has an olive-brown color. The fish’s name comes from rows of bioluminescent organs on its underside that reminded those who first discovered the species of the buttons on a midshipman’s uniform.
Andrew Bass, who is a Professor at Cornell University said the midshipman is among “the vocal champions of the marine environment along with whales and dolphins.” He added the production and hearing of vocal signals play a central role in the fish social interactions and reproductive behavior.
The study believes that the midshipman limits is singing to the night time because females are most receptive, or because their predators are less likely to hear their love songs.
Researchers also suggest that the fish night humming could be linked to evolution, saying that the midshipman body clock is part of their brain circuitry development from their most primitive, aquatic ancestors.
Another finding that described the study is that females are also sonic, but only territorial males used it to find a mate.
The mystery behind the midshipman’s singing
Bass confessed he got motivated to study the fish specimen after he read a paper written in 1924 by an academic called Charles Greene. The article revealed that the fish would hum at night. Bass stated that Mr. Greene referred to the plainfin midshipman as the California singing fish.
But for society, the midshipman fish and its singing have been subject to speculation. In the early 1980’s, people did not know what produced the night humming at Sausalito Bay, California, and started to believed the love song was an alien called.
People suspected the pumps of a nearby sewage plant was producing the sound, then, an underwater power line. Others thought the humming was part of a Navy experiment or even product of extraterrestrial activities.
Bass said that what people was hearing was merely the resonating sound of the male midshipman fish humming that traveled through their houseboats. And now that the study is published, the mystery is solved.
Source: BBC News