Document type: article published in Ouest France - Le Mag des Animaux
Author: Nathalie Truche
Preview: The sensitivity of fish has long been underestimated, as these silent animals are often perceived as being without consciousness or sensation. Yet recent research shows that they can experience pain when hooked or netted. Our article explains how pain and stress operate in fish, and how scientists assess how they feel. Understanding the mechanisms involved in their suffering allows us to better comprehend their welfare needs and take appropriate measures.
What is the mechanism of pain?
Pain is a biological reaction that enables an organism to detect and avoid injury [...]
What is stress? [...]
Do fish feel stress?
Fish do feel stress, as has been proved by numerous studies that have measured their cortisol levels after exposure to anxiety-provoking situations. When fish are captured, handled or placed in an unsuitable environment, their breathing accelerates and their behaviors change. Some become agitated, others adopt a lethargic state, and many lose their appetite. Further, prolonged exposure to stress can make them more vulnerable to infection, reducing their life expectancy.
How can you tell if a fish is suffering?
Scientists have conducted a number of experiments to determine whether fish are indeed suffering. Here are just a few examples:
A landmark experiment was carried out by biologist Lynne Sneddon, a specialist in pain in fish. In this study, rainbow trout were injected with bee venom or acetic acid into their lips, an area with many nerve endings. The results showed that these fish exhibited abnormal behaviors, frantically rubbing their mouths against the floor or walls of their aquarium, breathing more rapidly and refusing to feed. These reactions suggest that the fish were experiencing persistent pain and were actively seeking relief. When these same fish were given morphine, a powerful analgesic, their behavior returned to normal, proving that pain was not simply a reflex but a conscious sensation. In a different experiment, conducted by Dr Victoria Braithwaite, fish were placed in a tank where they could choose between a neutral space and one containing an analgesic substance. Injured fish preferred the analgesic-enriched environment, suggesting that they are able to detect and seek active relief from their pain, a behavior similar to that observed in mammals. Other studies have analyzed fish reactions to painful stimuli by measuring their levels of cortisol (a hormone linked to stress, see above). For example, when individuals are caught in nets or handled out of water, their cortisol levels rise significantly, indicating physiological distress as well as possible pain. Last, neurobiological research has demonstrated the presence of nociceptors and pain-processing structures in fishes' brains. Although different from those of mammals, their brains contain functionally similar regions, such as the pallium, which plays a role in sensory perception and emotional reactions. Brain imaging studies have confirmed that these regions are activated when a fish is exposed to a noxious stimulus.
Is a fishhook painful for fish?
A fishhook pierces particularly sensitive areas of the fish's mouth or throat, where many nociceptors are located. In addition to this physical injury, the animal experiences intense stress as it struggles to free itself and, if pulled out of the water, asphyxiates, a process comparable to suffocation in humans. Numerous studies have shown that fish that have been caught and released continue to show signs of stress and pain for several hours, calling into question the belief that the practice of "no-kill" causes no suffering.
Does net fishing cause fish to suffer?
Industrial net fishing also generates pain and stress in fish. Trapped in a confined space with hundreds or thousands of other fish, a fish will struggle to escape, sometimes leading to serious injuries (scrapes, contusions, and even fractures). Some fish, such as those caught in gill nets, become caught up by their gills or fins and suffer gradual asphyxiation if they are not quickly brought to the surface. In trawling, where a huge net is dragged behind a boat, some fish are often crushed under the weight of the others, causing internal lesions and haemorrhaging. On being hauled aboard, the fish undergo a brutal pressure differential that can bring about barotrauma, causing burst swim bladders, bulging eyes and damaged internal organs. Moreover, most fish caught in nets die of asphyxiation after being removed from the water, being unable to breathe outside their natural environment. Their suffocation lasts for anything from a few minutes to several hours in the case of stronger species. Fish are sometimes still alive when they are gutted or frozen, prolonging their agony.
How can suffering in fish be avoided?
A number ways to mitigate fish suffering have been identified: for example, amateur fishermen can use unbarbed hooks to reduce injuryc to the fish they catch, and can limit capture time to minimize stress. Some industrial fisheries are beginning to try out faster, less painful methods of slaughter, such as electronarcosis (using an electric current to stun the fish) or immediate exposure to iced water saturated with CO₂. However, these continue to be minority practices and are rarely employed out at sea. Better regulation of commercial fishing and the raising of public awareness ofthe conditions under which fish are caught would help improve the latters' fate. Consumers can get involved by choosing to buy products from fisheries and farms committed to animal welfare.
