Trout trauma puts anglers on the hook?
Published in The Royal Society -
Science News -
30 Apr 2003
Can fish feel pain? This is a question that
has troubled anglers and animal rights activists alike in recent
years. Research by a team of scientists from the Roslin
Institute and the University of Edinburgh to be published in a
forthcoming Proceedings B, a learned journal published by the
Royal Society, appears to provide the answer: "yes". This is the
first conclusive evidence indicating pain perception in fish. It
has previously been established that birds and mammals are
capable of experiencing pain.
This study was undertaken on rainbow trout and
demonstrates that not only are there nervous system receptors in
the head of the fish that respond to damaging stimuli, but that
application of short-acting noxious substances produce profound
behavioural and physiological changes in the fish over a
prolonged period comparable to those observed in higher mammals.
This indicates, the researchers believe, that fish can perceive
The presence of nociceptors - receptors that respond
preferentially to tissue damaging stimuli - in the rainbow trout
was determined using electrophysiological recordings. Neural
activity was recorded in prepared, anaesthetised fish whilst
mechanical, thermal and chemical stimuli were applied to the
head. "We found 58 receptors located on the face and head of the
rainbow trout that responded to at least one of the stimuli,"
says Dr Lynne Sneddon who led the research at the Roslin
Institute and is now working at University of Liverpool. "22 of
these could be classified as nociceptors in that they responded
to mechanical pressure and were stimulated when heated above
40ºC. Of these, 18 receptors also responded to chemical
stimulation and can be defined as polymodal nociceptors."
The polymodal nociceptors found in the trout
are the first to be found in fish and have similar properties to
those found in amphibians, birds and mammals including humans.
"Receptor diameter, thermal thresholds and mechanical responses
were found to be similar to those measured in higher vertebrate
groups," explains Dr. Sneddon. "However mechanical thresholds
were lower than those found in, for example, human skin. This
may be due to the more easily damaged nature of fish skin. The
threshold for mechanical stimulation appears to be similar to
that for mammalian eye nociceptors."
Nociception not enough
However the demonstration of nociception, the detection of
noxious, tissue damaging stimuli, in any animal is not enough to
prove pain perception. Nociception may sometimes be accompanied
by a reflex reaction such as withdrawal. To demonstrate pain
perception it is necessary to show that the animal’s behaviour
is adversely affected by a potentially painful experience and
these behavioural changes are not simple reflex responses.
Therefore the behavioural response to stimuli in fish was also
Bee venom or acetic acid was injected in the
lips of some trout, whilst other fish were injected with saline
solution or merely handled to form control groups. All fish had
previously been conditioned to feed at a feeding ring in their
tank where they were collected for handling and/or injection.
"Anomalous behaviours were exhibited by trout
subjected to bee venom and acetic acid," says Dr. Sneddon. "Fish
demonstrated ’rocking’ motion, strikingly similar to the kind of
motion seen in stressed higher vertebrates like mammals, and the
trout injected with acetic acid were also observed to rub their
lips onto the gravel in their tank and on the tank walls. These
do not appear to be reflex responses."
The acid and bee venom injected fish also took
almost three times longer to resume feeding activity compared to
the saline and handling control groups. The time to resume
feeding did not decrease in experiments with fish conditioned to
feed on ’softer’ food.
Hook line and sinker
"Our research demonstrates nociception and suggests that noxious
stimulation in the rainbow trout has adverse behavioural and
physiological effects. This fulfils the criteria for animal
pain," concludes Dr. Sneddon. "Previous work on fish has looked
at the elasmobranch family, such as stingrays, and primitive
vertebrates like the lamprey. These studies did not conclusively
show the presence of nociceptors. We believe that our study is
the first work with fish of the teleost family and the results
may represent an evolutionary divergence between the teleost and
The full title of this paper is:
Do fish have nociceptors: evidence for the
evolution of a vertebrate sensory system by Dr. Lynne U. Sneddon,
Dr. Victoria A. Braithwaite and Dr. Michael J. Gentle.
The full paper will be published via the
FirstCite website on Wednesday 30 April 2003 and will be part of
PROCEEDINGS OF THE ROYAL SOCIETY: Biological Sciences - Vol.
270, No. 1520 to be published in June this year. http://www.pubs.royalsociety.org
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Fact of the Day: Scientific evidence proves that fish do in fact, feel pain and react to it.