FISH BEHAVIOUR

Behaviour Relevant to Pain

Behavioural Evidence for Pain in Fish

Behaviour relevant to pain

• Feeding activity can be a basic reaction to pain. The initial reaction of the fish is often a sudden drop in feed consumption, resulting in cessation of feeding (Plumb, 1994).

• Swimming, the most general behaviour pattern of fish, involves the integrated effects of numerous physiological processes (Schreck, 1990). Estimation of swimming ability can provide a sensitive index to general stress and pain in fish. The swimming ability of fish under painful conditions, compared with that of fish not subjected to pain, is different. The pattern of swimming: swimming into shallow water, swimming lethargically at the surface, lying listlessly on the pond or tank bottom, floating downstream or swimming erratically can be an indicator (Plumb, 1994). Critical swimming speed and the length of time a certain swimming velocity can be maintained all may be used as an indicator of pain.

• Respiration is also thought to be a useful means to gauge the pain in fish. A difference between resting and active metabolism can be quantified simply by counting breaths (opercular beats) per minute or more precisely, by measuring respiratory gases. Respiratory movements, and even oxygen consumption all provide measures of toxicological stress which is related to pain by the fish can be observed (Fry, 1947).

• Other direct observations of behaviour, determination of the ability to learn or remember a particular behaviour can also be feasible (Sandoval,1979).

• However, behavioural responses to pain may differ considerably among fish species. Furthermore, little is known about fish specific behaviour response to pain: how can fish perform a particular behaviour? A behaviour pattern may be used as a useful index of pain and can be validated if it is not seen in the control group but is seen in the treated group.

Schreck, C.B. 1990. Physiological, Behavioural, and Performance Indicators of Stress. American Fisheries Society;

Plumb, J.A. 1994. Health Maintenance of Cultureed Fishes: Principal Microbial Diseases. CRC Press, Inc.

Sandoval, W. A. 1979. Odor detection by coho salmon(Oncorhynchus kisutch): a laboratory bioassay and genetic basis. Master's thesis. Oregon State University, Corvallis.

Fry, F.E.J. 1947. Effects of the environment on animal activity, The Ontario Fisheries Research Laboratory 68.

BEHAVIOURAL EVIDENCE FOR THE PERCEPTION OF PAIN BY FISH

• Fish response to pain is difficult to determine using traditional behavioural criteria.
• They exhibit all four basic responses to nociceptor stimuli:

1. Rapid startle reactions
2. Simple non-specific flight
3. Affective responses such as vocalisation
4. Co-ordinated reaction, such as biting the source of pain or rubbing the site of stimulation (Stoskopf, 1994)

• Responses to irritants or acute stimuli include pronounced reactions such as strong muscular and behavioural avoidance, and rapid respiration.
• Responses to chronic stimuli however may appear meagre or absent to the inexperienced observer.
• Fish react to chronic stimuli with unfamiliar responses such as colour changes or subtle alterations in posture and water column utilisation, and it would be an unjustified error to assume that fish do not perceive pain merely because their responses do not match those traditionally seen in higher vertebrates (Stoskopf, 1994).
• Behaviour also can be categorised into instinctive and learned behaviours.
•  

EXPERIMENT 1 (Ehrensing et al.., 1982)

• The response (agitated swimming) of goldfish to an electric shock (used to induce pain) was studied.
• Morphine was used to induce analgesia, and naloxone was used to reverse this analgesia.
• Increases in the concentration of morphine injected intracranially increased the intensity of shock needed to stimulate an agitated swimming response in a dose dependent way, and naloxone reversed this effect.
• The compounds thus behaved in a manner exactly analogous to the way they would behave in a rat subjected to a similar experimental protocol.
• This implies that fish react to analgesics similarly, and should thus feel pain similarly.
•  

EXPERIMENT 2 (Verheijen and Buwalda, 1988)

• It is often argued that the escape response of fish to aversive stimuli could be reflex in nature.
• Physically noxious ("pain") stimuli were administered separately by a) hooking the fish; and b) electrical stimulation via an electrode implanted in the roof of the mouth of the free-swimming fish.
• Responses of the hooked fish included rapid darting, spitting and shaking of the head.
• Responses of the fish subjected to electrical stimulation varied with the degree of painful stimulation.
• A mild stimulation resulted in a slight slowing of the heart beat and erection of some fins, while a highly effective shock caused wild erratic darting with bumping into the sides of the enclosure, and/or freezing.
• This implies that the escape response cannot be considered entirely reflex, and may reflect some conscious experience, as the fish can discriminate between the different stimuli and react accordingly.
•  

EXPERIMENT 3 (Beukema, 1970):

• Carp, initially hooked once and then released, learned to associate the bait with the hooking experience and subsequently avoided the bait.
• Up to three years later, the previously hooked fish were more difficult to catch than naïve fish.
• The remaining fish also became progressively more difficult to catch as the others were caught, implying that the unhooked fish were able to learn from the hooked fish that the experience was aversive.
• Carp are known to secrete pheromones which communicate their alarm to others when injured, and can also communicate their distress by vibrations carried through water.
•  

SUMMARY:

These studies show that fish contain endogenous opioid systems and neuromodulators similar to those found in mammals, and that analgesics modify the response of fish to painful stimuli in the same way as mammals. Fish avoid noxious stimuli, show a reluctance to resubmit themselves to noxious stimuli, and learn to associate neutral stimuli with painful stimuli, indicating that fish are indeed capable of feeling pain (Kestin, 1994).

REFERENCES:

• BEUKEMA, J. J. (1970) Angling experiments with carp: decreased catchability through one trial learning. Neth. J. Zool., 20: 81 – 92.
• EHRENSING, R. H., MICHELL, G. F. and KASTIN, A. J. (1982) Similar antagonism of morphine analgesia by MIF – 1 and naloxone in Carassius auratus. Pharmacology, Biochemistry and Behaviour, 17: 757 – 761.
• KESTIN, S. C. (1994) Pain and Stress in Fish. Bristol: Royal Society of the Prevention of Cruelty to Animals.
• STOSKOPF, M. K. (1994) Pain and Analgesia in Birds, Reptiles, Amphibians and Fish. Invest Ophthalmol Vis Sci., 35: 775 – 780.
• VERHEIGEN, F. J. and BUWALDA, R. J.A (1988) Do pain and fear make a hooked carp in play suffer? CIP – GEGEVENS. Utrecht. ISBN 90-9002167-1.

ON TO NEUROANATOMY OF FISH

BACK TO CONTENTS

BACK TO AWRG PAIN RESEARCH PAGE