The cruel sport of fishing causes considerable distress to fish.
Fish have nerves, as we do, to detect the elements that cause pain - heat, chemicals, and pressure.
In an experiment, twenty-two pain receptors were found on the face of rainbow trout.
In humans and other higher vertebrates, there are two types of nerve fibres used in pain transmission:
The fish’s eye is similar to the human eye, with the trigeminal nerve ending in receptors in the outer layer of the eye. Twenty-seven pain receptors were found in the eye of fish, and were as sensitive as in the human eye. (Ashley, 2006).
The Lamprey is one of the most primitive vertebrates. Nevertheless, nerve receptors responded to painful stimuli, such as puncturing or burning of the skin (Matthews, 1978).
Substance P is widely distributed in the brain, spinal cord, and peripheral nervous system in people. It is an important element in pain perception, and in the transmission of pain information into the central nervous system. Canadian researchers found the distribution of a P-like substance in the brain of brown ghost knifefish (Weld, 1992).
Fish pain specialist, and author of Do Fish Feel Pain, Dr Braithwaite, told the Los Angeles Times that, although simpler than our own, the brain of a fish has been found to be more similar than once thought. In the amygdala and hippocampus, our brains handle emotion, learning, and memory. The equivalent area has been found in the forebrains of fish. When this part is damaged, they lose their fear, forget how to navigate mazes, and are impaired emotionally.
Birds and amphibians lack the complex outer layer of the brain that humans do, the neocortex yet many studies have amply demonstrated pain and suffering in these groups, (Cooke, 2007).
Norwegian scientists applied electrical shocks to the tails of anaesthetised salmon. They were able to trace this painful stimulation to the telencephalon in the brain (Nordgreen, 2007). The German magazine, Der Spiegel, in 2011, reported on research that showed that this area had not previously been hightlighted, because rather than being in the inside, as in the human brain, it moves to the outside, after embryonic development.
Fish and mammals may have inherited the same brain functions from an ancient ancestor.
The scientists at the University of Seville, in an experiment, damaged the telencephalon of goldfish. This resulted in the fish being unable to learn to avoid an electric shock. Similar damage to the amygdala and hippocampus of mammals produces the same effect (Portavella, 2004).
The outer layer of the telencephalon is the grey matter of the pallium, involved in pain processing, and the equivalent of the cerebral cortex in humans.
In an experiment in Ireland, goldfish were pricked with a pin and a heat probe. Responses from this painful event were measured in the spinal cord, and in the brain, from the cerebellum through to the telencephalon (forebrain), where fish feel pain, (Dunlop, 2005).
The research shows that there is a neural pain pathway from the peripheral nervous system to the central nervous system, including the brain.
Fish have demonstrated that they remember the circumstances of painful experiences and will afterwards seek to avoid the same situation.
Dutch researchers used anglers for three days to fish for pike, which had never been fished before, with live bait or spinner hooks. The fish were then tagged and returned to the water. It was then found that pike previously only hooked once by a spinner, rarely took it again, and avoided spinners for the remaining five days (Beukema, 1970).
At Belfast University, goldfish and trout were also given mild electric shocks when they entered a particular part of their tank. The fish reacted with rapid breathing and an increase in their blood cortisol, an indication of stress. They remembered to keep to one end of the tank, thus avoiding pain (Dunlop, 2006).
In an experiment by other researchers, goldfish were conditioned to expect an electric shock after a light was shown to them. Their fear produced a slowing of the heart when the light preceded the shock. However, when an analgesic, lidocaine, was injected into the brain (cerebellum) of other goldfish, it prevented the goldfish from feeling pain, and so they did not show fear when the light was shone (Masayuki, 2006).
Cod and bream learn to associate the sound of trawler with later contact with the fishing gear, causing them to be frightened by the sound alone, leading to decreased catchability during repeated trawls. Fish who escape gear may risk being unable to feed properly afterwards, or may be eaten, as they recover from stress or bodily harm. A single traumatic encounter can be remembered, and avoided, for several months. Cod, in the lab, have also learnt to avoid baited hooks (Brown, 2011).
In an experimental tank, zebrafish chose to live where there were plants and gravel, instead of a barren environment. However, when they were injected with a pain-causing chemical, they preferred to spend time in the barren environment where there was painkiller in the water (Sneddon, 2011).
Not only can fish detect and perceive painful events, but they also show disturbed behaviour.
Fish, like mammals, have been reported to make sounds when pain is felt. Although normally silent, wounded European weather loach vocalize their pain using their swim bladders (Chervova, 1968).
Scientists in the 1930s discovered that wounded minnows released a chemical that caused fear in other minnows. Scientists in Singapore isolated the chemical in zebrafish, who froze in place (Jesuthasan, 2012).
Fish will often not swim close to an object that they have not encountered before. Trout that had acetic acid (vinegar) 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 the normal cautious response if they were given morphine later. The researchers said that the painful acid distracted the attention of the fish. For this to be happening, the fish must be consciously aware of the negative experience of the pain (Sneddon, 2011).
At Liverpool and Manchester Universities, England, trout once more had acid injected into their lips. 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 (Sneddon, 2009).
FISH SPECIES VARY IN THEIR RESPONSE TO PAIN(Pain)
It can be demonstrated that fish feel less, or no, pain, when blocked by analgesic drugs. Fish also possess natural chemicals in their brains that reduce pain. If we were to believe that fish do not experience pain, why would these chemicals be present?
In New Orleans, scientists applied electricity to fish to produce an "agitated swimming response." After fish were injected with morphine, the voltage had to be increased to achieve the same response. However, when naloxone was injected, the analgesic effect of morphine was blocked (Ehrensing, 1981). Similar results were found by researchers in Portugal (Correia, 2011).
Researchers in Scotland injected acetic acid into the lips of rainbow trout. The fish rocked on either pectoral fin from side to side, and rubbed their lips into the gravel and against the sides of the tank. The respiration rate almost doubled. They were then given morphine. This reduced the abnormal behaviour, and calmed down the respiration. The study said that these pain-related behaviours were not simple reflexes (Sneddon, 2003).
At only five days after being fertilized, zebrafish larvae were exposed to weak acid, causing them to slow their swimming. However, when painkillers - aspirin, lidocaine, or morphine - were dissolved in their tank, before the acid was later added, they swam normally (Sneedon, 2017).
Many animals have opiate receptors, which are involved in regulating pain in the body. Fish also have their own natural painkillers. Researchers in England found opiate receptors in the brains of goldfish, catfish, African lungfish, and rainbow trout (Sneedon, 2004).
Russian scientists held fish in a water chamber. They applied short bursts of electricity to the tail fin. which jerked in response. Painkillers were given to the fish, and this allowed higher voltages to be applied before the fish responded. However, if a chemical known to block painkillers was then given, the fish once more jerked their tails in response to the lower voltages. When the experiment ended, it was found that different species took varying times to recover. The sturgeon swam slowly and preferred to lie at the bottom of the tank - this lasted for five days. The scientists concluded that fish feel pain, which affects their physiology and behaviour (Chervova).