Fish farting may not just be hot air
By Celeste Biever
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-
"It sounds just like a high-pitched raspberry," says Ben Wilson of
the University of British Columbia in Vancouver, Canada (Listen
here , .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.
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
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)
Air bubbles much like ship props issue and would bring proteins to
surface and impact conductivity and provide a mechanism to cause bio
cirrus particle connection.