Pain

Not only can fish detect and perceive painful events, but they also show disturbed behaviour.

  • Loach make sounds when wounded
  • Pain can cause rapid breathing
  • Pain can cause reduced swimming
  • Pain can cause feeding to stop
  • Pain can cause rocking backwards and forwards
  • Goldfish rubbed their lips on gravel and tank walls when injected with vinegar
  • Injured minnows warn others by chemical release

VOCALISING PAIN

Although fish are normally silent, Russian scientists (Chervova) found that the wounding of European weather loach caused the fish to vocalize in pain using their swim bladders.

SMELLING FEAR

Scientists in the 1930s discovered that wounded minnows released a chemical that caused fear in other minnows. Scientists in Sigapore (Jesuthasan, 2012) have isolated the chemical in zebrafish, who froze in place.

PAIN OVERRIDES FEAR OF NEW OBJECTS

rainbow-trout fish pain cruelty

Fish will often not swim close to an object that they have not encountered before. Researchers in Scotland (Sneddon, 2003) found that trout, that had vinegar (acetic acid) injected under their skin, were less wary than fish who had not had the injection, when a lego tower was placed in their tank. The fish showed a normal cautious response if they were given morphine later.

The researchers said that the painful vinegar distracted the attention of the fish. For this to be happening, the fish must be consciously aware of the negative experience of the pain. The scientist concluded that, "the criteria for animal pain have been fulfilled for the trout."

ABNORMAL BEHAVIOUR IN TROUT AFTER VENOM OR VINEGAR

Researchers, again in Scotland (Sneddon, 2003, 2), injected into the lips of rainbow trout either bee venom or vinegar. A control group was handled but received no injection.

The effects on the fish was a near doubling of respiration, stopping of feeding for 3 hours, and reduced swimming. They rocked back and forth, balancing on either pectoral fin, while resting on the gravel, and they also rubbed their lips into the gravel and tank walls.

TROUT HIDE SIGNS OF PAIN

Researchers at Liverpool and Manchester Universities (Sneddon, 2003, 3), in a separate experiment, injected vinegar once more into the lips of trout.

After their painful experience, when individual fish were returned to a familiar social group they showed reduced aggression. When the fish were returned to an unfamiliar social group, they showed the usual level of aggression, suggesting that maintaining dominance status took priority over showing signs of pain.

The scientists concluded that fish are considerably affected by pain, and that the perception is not just a simple reflex. The experiment showed that fish are able to perceive and manage the pain felt.

CHEMICAL INDICATION OF STRESS

Two well known indicators of stress in animals are

  • adrenalin
  • cortisol
These are also used by fish.

"Stress in fish, as in other animals, results in two types of endocrine response, the adrenergic response, resulting in increased plasma concentrations of adrenaline and noradrenaline, and the hypothalamo-pituitary-interrenal response, culminating in an increased plasma cortisol concentration."
The Endocrinology of Stress, page 97 Author: Sumpter Year: 1997 Where: Cambridge University Press

FISH SPECIES VARY IN THEIR RESPONSE TO A PAIN

Fish Species
Swimming
Ventilation Rate
Feeding
Abnormal Behaviour
Rainbow Trout reduced increased reduced yes
Carp same same reduced yes
Zebrafish reduced increased reduced yes
Adapted from Reilly, 2008, Roques, 2010, Sneedon, 2011
Reilly, 2008, Behavioural analysis of a nociceptive event in fish: Comparisons between three species demonstrate specific responses, Applied Animal Behaviour Science, 114, pp. 248-259
Roques, 2010, Tailfin clipping, a painful procedure: Studies on Nile tilapia and common carp, Physiology & Behavior, 101, pp. 533-540.
Sneedon, 2011, Pain Perception in Fish Evidence and Implications for the Use of Fish, Journal of Consciousness Studies, 18, No. 9-10, pp. 209-29
Fish Pain