Subject: Fish farting may not just be hot air
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| Fish farting may not just be hot air
| 00:01 05 November 03 NewScientist.com news service
| Biologists have linked a mysterious, underwater farting sound to bubbles
| coming out of a herring's anus. No fish had been known to emit sound from
| its anus nor to be capable of producing such a high-pitched noise.
| "It sounds just like a high-pitched raspberry," says Ben Wilson of the
| University of British Columbia in Vancouver, Canada (Listen here
| <http://www.zoology.ubc.ca/~bwilson/Herring_sound.wav>, .wav file). Wilson
| and his colleagues cannot be sure why herring make this sound, but initial
| research suggests that it might explain the puzzle of how shoals keep
| together after dark.
| "Surprising and interesting" is how aquatic acoustic specialist Dennis
| Higgs, of the University of Windsor in Ontario, describes the discovery. It
| is the first case of a fish potentially using high frequency for
| communication, he believes.
| Arthur Popper, an aquatic bio-acoustic specialist at the University of
| Maryland, US, is also intrigued. "I'd not have thought of it, but fish do
| very strange and diverse things," he says
|
| Grunts and buzzes
| Fish are known to call out to potential mates with low "grunts and buzzes",
| produced by wobbling a balloon of air called the swim bladder located in
the
| abdomen. The swim bladder inflates and deflates to adjust the fish's
| buoyancy.
| The biologists initially assumed that the swim bladder was also producing
| the high-pitched sound they had detected. But then they noticed that a
| stream of bubbles expelled from the fish's anus corresponded exactly with
| the timing of the noise. So a more likely cause was air escaping from the
| swim bladder through the anus.
| It was at this point that the team named the noise Fast Repetitive Tick
| (FRT). But Wilson points that, unlike a human fart, the sounds are probably
| not caused by digestive gases because the number of sounds does not change
| when the fish are fed.
| The researchers also tested whether the fish were farting from fear,
perhaps
| to sound an alarm. But when they exposed fish to a shark scent, there was
| again no change in the number of FRTs.
|
| Night waves
| Finally, three observations persuaded the researchers that the FRT is most
| likely produced for communication. Firstly, when more herring are in a
tank,
| the researchers record more FRTs per fish.
| Secondly, the herring are only noisy after dark, indicating that the sounds
| might allow the fish to locate one another when they cannot be seen.
| Thirdly, the biologists know that herrings can hear sounds of this
| frequency, while most fish cannot. This would allow them to communicate by
| FRT without alerting predators to their presence.
| Wilson emphasises that at present this idea is just a theory. But the
| discovery is still useful, he says. Herring might be tracked by their FRTs,
| in the same way that whales and dolphins are monitored by their
high-pitched
| squeals. Fishermen might even exploit this to locate shoals.
| There may even be a conservation issue. Some experts believe
human-generated
| sounds can damage underwater mammals. Now it seems underwater noise might
| disrupt fish too.
| Journal reference: Biology Letters (DOI: 10.1098/rsbl.2003.0107)
| Celeste Biever
|
| http://www.newscientist.com/news/news.jsp?id=ns99994343
Nick Zarlinga
"If we ignore nature.....maybe it'll go away."
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