fish do not feel pain?
In the twentieth century, the prevailing view was that fish do not feel pain.
The fish brain is simpler than the brain of mammals, and it lacks areas that in humans and other mammals are responsible for processing information related to pain.
In 2003, pain receptors were discovered in fish, and even though the fish brain is simpler, it was found that they respond to pain in ways similar to humans.
When a fish feels pain, for example from an electric shock or an injection, its breathing accelerates, and after the painful experience it rubs the injured area and changes its swimming speed, sometimes speeding up and sometimes slowing down.
It avoids for hours to days returning to the environment where it experienced the pain, indicating that this is not only an initial response but learning that affects its behavior in the long term.
If painkillers are given, for example aspirin or morphine, the behavior indicates a reduction in pain and the fish returns more quickly to the environment where it experienced the pain.
The conclusion is that there is a similarity between the pain experience of fish and our own pain experience.
The fishing industry catches about a trillion fish each year.
The most common and simplest method of killing a fish is to remove it from the water and wait for it to die from suffocation.
The gills of the fish are responsible for removing carbon dioxide and absorbing oxygen.
Outside the water they stick together, cannot continue exchanging gases with the environment, and carbon dioxide accumulates in the blood and later in the brain.
The fish gasps in an attempt to bring oxygen into the blood.
The rise in carbon dioxide levels in the body increases the acidity of the blood, which causes additional pain, and finally, when the acidity level in the brain rises, the fish loses consciousness. There is no definitive evidence that pain receptors are activated when the fish is removed from the water, but there is an increase in the level of the hormone cortisol, which is secreted in states of stress and distress, and the fish twists and writhes in what appears to be a desperate attempt to return to the water.
It therefore seems that the fish experiences pain when removed from the water, beyond instinctive spasms.
It is difficult to measure the suffering of animals, but researchers examined in a new study the pain experience of fish removed from the water.
They recently developed a method that combines the intensity of suffering the animal experiences and the duration of time it experiences it.
If there were a single measure for the pain animals feel during treatment, it would be possible to improve the way we treat animals, including farm animals.
The authors of the study said in a publication that the public is more aware of the impact of food production processes on animal welfare, and this rise in awareness is reflected in attempts to label products and change legislation and policy to prioritize animal welfare. Their findings provide the first quantitative assessment of the suffering of fish on their way to the plate.
To assess the suffering experienced by fish, the researchers focused on a specific species of trout. They relied on previous articles and evaluated the stages the fish goes through from the moment it is removed from the water until it loses consciousness.
The fish was considered unconscious when no reflexes appeared in its eyes and they did not respond to light.
According to the article, the fish goes through four stages.
It is exposed to air, carbon dioxide levels and blood acidity rise, it experiences metabolic exhaustion, and finally it loses consciousness.
The researchers estimate that from the moment the fish is removed from the water until just before it loses consciousness, it experiences pain.
In some studies the fish lost consciousness within two minutes, and in others within about twenty minutes.
The researchers estimated that between two and twenty five minutes pass from the moment the fish is removed from the water until it loses consciousness.
The time estimates vary widely because these are different studies that examined fish of different sizes and at different temperatures.
The study provides an initial assessment of the pain experience the fish undergoes on its way to the plate.
However, the researchers relied on previous articles and did not conduct primary and direct research under controlled conditions.
Do pain receptors operate when the fish is removed from the water.
How do water temperature and fish size affect the length of time it experiences pain.
These issues need to be studied to ensure optimal treatment of captured fish.
When we know how long their pain lasts and how intense it is, and when the information is made accessible to decision makers, it will be easier for them to plan and set policy that reduces the suffering of fish.
There are solutions that may reduce the pain of fish, for example electric shock that leads to loss of consciousness before the fish is removed from the water, or the use of painkillers and anesthetic substances.
However, to decide whether to adopt these solutions, additional large scale industrial studies will be required.
In addition, reducing the pain of fish will cost money, and it is likely that fishermen and producers will pass this cost on to the consumer, which will raise the price of fish.