It's a little boy's dream: talking through farting. But it may be a part of everyday life for herring. A new study finds that the fish make noise by squeezing air bubbles out of their backsides. Researchers believe the noise could be used for communication.
Compared to most other fish, herring have great hearing, and scientists have wondered whether they use sound to communicate among themselves. Indeed, the fish make a variety of whistles and thumps.
To investigate herring sounds, two groups of researchers recently lowered microphones and cameras into schools of fish. Magnus Wahlberg, now at Aarhus University in Denmark, and colleagues listened after dark in the ocean. The team noticed that herring often release bubbles from their anuses when scared or during ascent or descent. They reported this curious finding earlier this year in Aquatic Living Resources.
To get an even closer look, Ben Wilson of Simon Frasier University in British Columbia, Canada, set up tanks in the lab. Wilson's group videotaped the fish and correlated the bubble blowing with the sounds they recorded, which they termed fast repetitive ticks (FRTs). Wilson's group found that the herring need to gulp air at the surface for continued FRTs; when the researchers blocked the herring's access to air, the fish FRTed for a little while then stopped. The team also noted that the herring made this particular noise just as darkness was falling, when they gather. This suggests that the FRTing has a social function, Wilson and colleagues report online 5 November in Biology Letters.
Although related fish have been caught farting nondescriptively, these new herring FRTs are distinctive. "They're really cool signals," says acoustic biologist Michael Fine of Virginia Commonwealth University, Richmond, because they're streams of distinct pulses. No one knows for sure what purpose farting serves in any fish, but neuroscientist Arthur Popper of the University of Maryland, College Park, says, "It's conceivable that they're using it for communication. Fish do the weirdest things."