"Throwing your guts
up" may not be the most elegant phrase to describe the action
of vomiting, but in some fish species it is certainly an accurate
one.
UK researchers have
shown that a thornback ray will literally turn its stomach inside
out to eject an unwanted meal. For a very short time, even the
stomach itself will be pushed out through the mouth to get a good
cleaning.
The ray thrashes
its head from side to side to make sure everything is washed away.
Many animals vomit.
It is a very important protection mechanism designed to rid the
body of dangerous materials that are either toxic or indigestible.
And although the type
of vomiting reflex seen in the thornback may sound dramatic, it
is probably more common than was thought.
How
to invert a tube
"We don't
really know the mechanism involved but it obviously involves some
muscular movements," Dr David Sims, from Aberdeen University's
Department of Zoology, told BBC News Online.
"The
problem is how to invert a tube. When you take your socks off
they always go inside out and that is what the ray has got to
do. So, muscle contractions of the gut and throat area are probably
responsible."
Dr Sims
and colleagues watched and filmed several trawler-caught thornbacks
(Raja clavata) swimming in their laboratory.
The rays
were given an injection of veratine hydrochloride to make them
sick. This usually occurred within 10 minutes of the emetic being
administered. Vomiting was frequent, with one animal "chucking
its guts up" nine times in four discrete bursts.
Poisons
and parasites
The whole
procedure is very short with the stomach ejected, cleaned and
swallowed again in about four seconds.
"This
behaviour has been seen in rays and sharks and is therefore more
widespread than is currently realised," Dr Sims said. "It is a
way for these creatures that eat prey whole to get rid of indigestible
materials. It would work for poisons and parasites as well."
Certain
frogs and toads can also do it, except they actually use a hand
to clean the stomach when it is hanging outside the mouth.
By studying
different creatures that display similar behaviour, scientists
might gain fresh insight into the evolution of the autonomic nervous
system.
This
controls the many organs and muscles within the body cavity that
function in an involuntary, reflex manner.
