A

n American folktale tells of how theGood Lord

createdishandilled the rivers with thesecrea-

tures. Theinestand most handsomeish ofall

was thecatish. The Good Lord made catish

with brilliantly coloured scales that sparkled

hues of red, blue and gold as they swam in the shallow waters.

The Good Lord enjoyed walking along riverbanks and seeing

these beautiful creatures. Then one day the Good Lord came

upon the Devil who was seated by a river. The Devil was

plucking the scales off a catish so he could fry it for dinner.

The catish was wincing with pain as each scale was pulled out

and this angered the Good Lord. The Good Lord threw the

catish back into the water. To ease its pain, the catish swam

to the bottom of the river and slithered about in the mud. The

pain disappeared and from that day on catish no longer had

scales and instead became covered in slime, making themdii-

cult for the Devil tocatch.

It’s very easy to conclude that a ish feels pain if it winces

every time a scale is plucked. Plucking an eyebrow or pulling

sticky plaster off your skin causes a twinge of pain, so it’s not

unreasonable to assume that a grimacing ish also feels pain.

However, looks can be deceiving. The question of whether ish

feel pain has become a heated academic debate involving scien-

tists and philosophers from diverse ields including neuro-

science, psychology, medicine, ethology, systems biology, animal

welfare and robotics. The resolution of this question has impor-

tant implications for understanding the nature of consciousness.

Given that ish respond to stimuli that in humans cause

pain, why is the question that ish feel pain such a hard problem?

Assessing pain in humans seems to be a relatively simple matter.

All we need to do is to prick someone’s big toe with a pin and

ask whether they felt pain.

But what happens if that person can’t speak and tell us what

they are feeling? Again that seems to be easily resolved. We

could watch the person to see if they withdrew their foot

following the pinprick. Measuring the distance moved by the

foot could provide a quantitative index of the amount of pain.

But this is where it actually begins to get tricky.

What happens if the person has suffered a spinal cord injury

and they can’t feel any sensations arising from their feet. Some

paraplegics with complete spinal cord injury can still physically

respond to stimuli, such as a pinprick to the sole of the foot,

despite not experiencing any pain sensation. These bodily

responses occur non-consciously (i.e. without being aware or

feeling).

Many different types of human behaviours can occur non-

consciously. Extreme examples include walking and driving

while asleep. A sleepwalker can get out of bed and walk around

objects and even operate machinery while being totally obliv-

ious to what they are doing. Observing body movements is

clearly not an appropriate way of assessing the feeling of pain.

So how do we interpret the response of the catish to the

Devil’s plucking of scales? We have learned that merely observing

behaviours can be misleading. A better way of inferring pain is

needed.

In2003, Lynne Sneddon in theUnitedKingdom thought

she had found this when she began observing the response of

ish to injections of acetic acid (vinegar) into their lips. She

injected ive trout and found that they subsequently displayed

anomalous behaviours not seen in ish injected with saline (salt

water). The acid-injected trout appeared to rock on their ins

or rub their lips into the gravel on the bottom of the holding

tank, much like the catish in the folktale. Although they only

performed these movements less than two times per minute, she

still likened it to the way humans sometimes vigorously rub an

injured area. She then found that these behaviours seemed to

disappear if the ish were subsequently injected with morphine.

This study is often touted as deinitive evidence that ish feel

pain.

30 | APRIL 2016

Do Fish Feel Pain?

BRIAN KEY

If you want to know whether your pet goldfish can feel pain you had better look inside its head

to see if it has the brains for it.

... are fish equipped with the

specialised forebrain subregions as

well as the bidirectional network of

fibres and interconnections that are

necessary for awareness and the

feeling of pain?