Despite the common perception that fish can’t feel pain, there is growing evidence that fish and crustaceans are in fact sentient beings capable of experiencing pain, fear and distress. The information below is an overview of the evidence for fish feeling pain & suffering, and the impacts this has on welfare.
It has been argued that because fish lack the neocortex responsible for pain perception in the mammalian brain, they are unable to feel pain. However, some experts respond to this by saying:
Studies of the sensory systems, brain structure and functionality provide evidence that different neurological structures provide at least some degree of sentience and pain reception in fish. For example, the forebrain of fish contains the dorsomedial and dorsolateral telencephalon, these brain structures are thought to perform the same function as the amygdala (emotions & fear responses) and hippocampus (spatial learning & memory) in mammals. Simply put, different structures have evolved to fulfil the same role. Therefore, although their perception of pain and suffering may not be identical to ours, fish do have brain structures capable of feeling fear and pain.
There is also good evidence that some invertebrates such as crustaceans also have the capacity for fear and pain, even though they lack a vertebrate brain system. More information on Crustacean Pain can be found HERE.
The following responses provide evidence of a fish’s ability to elicit a physiological pain response:
- Fish react to painful stimuli with primary, secondary and tertiary stress responses. These responses involve increasing levels of cortisol and catecholamines, and an increase in heart rate, blood flow and metabolism. This is the same response observed in mammals.
- Fish have very similar nociceptors (pain receptors) and associated central nervous pathways to other vertebrates. These pathways send information to the same functional areas of the brain in fish as in other animals.
- Endogenous opioids are produced by the brain to reduce pain. They work by interacting with opioid receptors, and all 3 types of opioid receptors known in mammals have been identified in studied fish species. There is also an elevation in the level of precursor chemicals in fish in response to pain, just as there is in people.
- Analgesics (pain killers) work on fish to reduce the behavioural and stress response to harmful stimuli in the same way that is seen in other vertebrates.
- Scientists have identified that different brain activity occurs in fish in response to a noxious (harmful) stimulus compared to a harmless stimulus, e.g., being touched with a heated prod vs. stroking with a paint brush. This shows activation of the brain structures involved in pain processing and indicates that the reaction to a harmful stimulus is not merely reflexive in fish.