South Coast ECOfishers

Like vegans have to prove absolutely that they don't cause pain to plants. Come off the grass. Enlighten yourself. Have a read of this:

A critique of the paper: ?Do fish have nociceptors: Evidence for the evolution of a vertebrate sensory system?
published in Proceedings of the Royal Society, 2003 by Sneddon, Braithwaite and Gentle.
James D. Rose, Ph.D.
Department of Zoology and Physiology
University of Wyoming
Laramie, WY 82071
USA

The paper by Sneddon, et al. is flawed and does not provide any legitimate evidence that trout are capable of
feeling pain. There are numerous problems with methods and data interpretation in this paper but this critique will
focus only on those of greatest significance. First, an explanation of the invalid claims for evidence of pain will be
presented, followed by an account of the misinterpretations of the behavioral results.
Flaws in the argument for a demonstration of pain.
1. The authors? definitions of pain and nociception are invalid, consequently this paper does not actually
deal with pain (a conscious experience), it deals only with nociception (unconscious responses to
noxious stimuli). Pain, as defined by the International Association for the Study of Pain is purely a conscious
experience, with a sensory component and a component of emotional feeling (suffering). In contrast to this
conscious experience of pain, the unconscious detection, transmission and response to noxious stimulation by
lower levels of the nervous system is and defined as nociception - not pain. According to Sneddon, and
associates, any behavior that is a reflex would be evidence of nociception but any behavior more complex than a
reflex would be evidence of pain. This way of distinguishing pain from nociception is invalid because there are
clearly complex, non-reflexive behaviors that can be purely nociceptive and unconscious. For example, humans
with extensive damage of the cerebral hemispheres can still make a complex of responses including facial
grimaces, vocalizations, struggling and avoidance reactions to noxious stimuli, but they are unconscious and
unable to experience pain. From the definition of pain used by Sneddon and associates, it would be concluded
that these unconscious humans are feeling pain rather than making purely unconscious, nociceptive responses,
which is clearly erroneous. There are many other examples of complex, non-reflexive, even distress-like
behaviors that can be performed unconsciously. A person having a night terror, for instance, will show a
compelling fear-like display, including a scream, terrified facial expression, elevated heart rate, sweating and
dilated pupils, even though they are unconscious and in such deep sleep that they are difficult to awaken. The
point is that complex behavioral displays that seem to reflect distress can be purely unconscious ? even in
humans. It should not be hard to appreciate that the behaviors of which a fish is capable could be unconscious as
well.
2. In order to show that a fish experiences pain, it is necessary to show that a fish has consciousness.
Without consciousness, there is no pain. None of the fish behaviors in this paper require the involvement of
consciousness and the authors don't even deal with this essential issue. Furthermore, as I have shown in my
2002 Reviews in Fisheries Science paper, there is extensive scientific evidence that pain and consciousness
depend on very specific brain regions, namely specialized neocortex regions of the cerebral hemispheres. These
specialized neocortical regions perform the additional levels of neural processing, beyond unconscious
nociception, that make the experience of pain possible. These brain regions are absent in fishes and there are no
alternative brain systems to perform the same functions. Consequently, there is no neurological basis for
assuming that a fish might have a capacity for consciousness or pain. Thus, the burden of proof that trout are
conscious and potentially capable of feeling pain remains on these authors. They dealt with this issue only by
citing previous studies that also used invalid criteria for pain, such avoidance learning, which actually occurs
unconsciously. Only anthropomorphic speculation would lead one to conclude that the trout in this study were
experiencing pain.
The behavioral results allegedly showing evidence of pain were misinterpreted.
1. The behavioral studies were done by injecting large volumes of one of three solutions: bee venom, acetic acid
solution or saline, into the jaw of rather small trout. For the sizes of the fish used, these injections of liquid
would have been equivalent to injecting 100 milliliters (more that 3 ounces) of solution into the lip of a
human. Bee venom contains a great variety of toxins that affect the nervous system and cause a hormonal
stress response in addition to stimulating receptors signaling tissue injury. In spite of the large dose of venom
or acid, the activity level of these fish was not affected, they did not hide under a shelter in the tank and
they resumed feeding in less than three hours. Furthermore, fish that received no injection at all or fish that
received a saline injection did not feed, on average, for an hour and 20 minutes, showing that a large saline
injection produced no more effect than just handling. The acid and venom-injected fish also showed an infrequent
rocking behavior that may have reflected a difficulty by the fish in maintaining an upright posture, given the
magnitude of the toxic chemical trauma created by the injection. But, even if the infrequent rocking was a
response to nociceptive stimulation of the mouth, there is no reason to believe that it is any more than an
unconscious nociceptive response, rather than an indication of ?pain?.
2. Sneddon and associates also state that the acid-injected fish rubbed their mouths against the gravel (they don?t
say how often), but the venom-injected fish did not. They concluded that mouth rubbing was an indication of pain
because mammals, including humans, rub injured tissues to alleviate nociceptive input. If so, why did the venominjected
fish, that were also supposed to be in pain, not perform this behavior? In addition, injections of irritants
into skin tissues is known to cause hyperalgesia, where skin becomes hypersensitive, like the effect of a sunburn.
Who rubs sunburned skin against gravel to alleviate the pain? At one point in the paper, Sneddon and associates
say that feeding was suppressed because the fish were avoiding mouth stimulation, which would cause ?pain.?
But later, they say that mouth rubbing was a way of reducing ?pain.? These are contradictory interpretations and
you can?t have it both ways. Their interpretations of the mouth-rubbing behaviors don?t make sense nor do they
show conscious experience of pain.
3. One of the few effects actually produced by the acid or venom injections was an elevated opercular beat rate
(breathing). This response could have resulted directly from gill irritation due to leakage or blood borne spread of
the acid or venom injections, but even if increased opercular beat rate was due to nociceptive stimulation of the
mouth, this unconscious movement proves nothing about conscious pain.
4. One caveat regarding the behavioral data described above is the fact that some of the statistical analyses were
not done correctly. Data for opercular beat rate and for time to resume feeding were analyzed by one-way
analysis of variance, but conclusions were made about specific group differences in these measures. With this
type analysis, it is not legitimate to conclude that one group (e.g. acid or venom injected differed from any other
group (e.g. handeled or saline injected), but the authors made such conclusions, nonetheless. Given the sizes of
the standard errors of the means for these data, however, the group differences reported by the authors would
probably have been substantiated following proper statistical analysis.
To summarize, the most impressive thing about the acid and venom injections was the relative absence of
behavioral effects, given the magnitude of the toxic injections. How many humans would show little change in
behavior or be ready to eat less than three hours after getting a lemon-sized bolus of bee venom or acid solution in
their lip? Rather than proving a capacity for pain, these results show a remarkable resistance to oral trauma by the
trout. It comes as no surprise, then, that many anglers have had the experience of catching the same fish repeatedly
within a span of a few minutes. Of course predatory fishes, including trout, feed avidly on potentially injurious prey like
crayfish, crabs and fish that have sharp spines in their fins ? which further indicates that these fish are not highly
reactive to noxious oral stimuli.
In addition, Sneddon and associates claim to have presented the first evidence for nociceptive sensory receptors
in fish, but their results were neither wholly original nor unexpected. In my 2002 Reviews paper, I cited a 1971 study
by Whitear that showed the presence of C-fibers in fish. C-fibers are a principal type of nociceptive receptor, so there
was very good reason to assume that trout would have nociceptive receptors. Another technical issue arises in the
authors? description of their procedure for decerebration of trout in order to make them ?insentient.? The term sentience
is vague and has no standard scientific meaning, but apparently Sneddon, et al. were performing this decerebration in
order to eliminate any potential pain that they assumed was within the capacity of the trout. The usual means of
producing a decerebration is to remove all brain tissue above the midbrain. According to Sneddon, et. al, however,
they removed the ??olfactory and optic lobes and cerebellum?? This is peculiar and counterproductive because the
entire pathway for nociceptive information from the periphery through the brainstem to the cerebral hemispheres would
have remained intact in these fish, since the ?ofactory lobes? but not entire cerebral hemispheres would have been
removed according to this description. If fish could feel pain, as the authors contend (and I dispute), these fish
probably would have.
The bottom line of this critique is that any attempt to show pain in fish must use valid criteria, including
proof of conscious awareness, particularly a kind of awareness that is meaningfully like ours. This is not
something that can be taken for granted, because on neurological and behavioral grounds it is so improbable that fish
could be conscious and feel pain. Furthermore, the behavioral results of this study show that in spite of very large
injections of acid solution or venom, the fish showed little adverse effect, hardly supporting the claim that they were in
pain.
Cited reference: Rose, J. D. 2002. The neurobehavioral nature of fishes and the question of awareness and pain.
Reviews in Fisheries Science, 10: 1-38. This paper can be obtained in electronic form from the author.