Nociception is the unconscious detection by the nervous system that damage is occurring somewhere.
Nociceptors are sensory receptors that respond to potentially damaging stimuli by sending nerve signals to the spinal cord and brain. In 2003 Lynne Sneddon was able to demonstrate the presence of nociceptors on the face and snout of the trout.
[30] The receptors responded to touch, heat and chemical stimulation by sending an electrical signal through the trigeminal nerve to the brain.
[31] However, Rose et al. (2013)
[20] point out that a typical human cutaneous nerve contains 83% C type trauma receptors (the type responsible for excruciating pain in humans), but the same nerves in people with congenital insensitivity to pain only have 24-28% C type fibres. Sneddon showed that rainbow trout on the other hand have only around 5% C type fibres, while sharks and rays have 0%
[32] The absence of C type fibres indicates that signalling leading to pain perception is likely to be impossible for sharks and rays, and the low numbers (5% C fibres) suggest this is also highly unlikely for fish (Rose et al. 2013). From this, Rose et al (2013) concluded there is scant evidence that sharks and rays possess the nociceptors required to initiate pain detection in the brain, and fish are evolutionarily little more advanced than sharks in this respect. Rose et al (2013) concluded that sharks and bony fish have survived well in an evolutionary sense without the full range of nociception typical of humans or other mammals, probably because it would otherwise be disadvantageous to their survival in the aquatic environment.
[20]
