In this experiment, goldfish were pricked with a pin. Responses from this painful event were measured in the spinal cord, and in the brain, from the cerebellum through to the telencephalon (forebrain), where it is thought that fish feel pain.
Responses were also found when a heated prod was used.
The speed of the response suggested that the pain nerves were A and C fibres, which are known to be used in pain transmission in people.
The research shows that there is a neural pain pathway from the peripheral nervous system to the central nervous system, including the brain.
RESPONSES TO PIN PRICK, MEASURED FROM SPINAL COLUMN TO BRAIN
"Nociceptive responses to a repetitive pin-prod stimulus in goldfish and trout were assessed. Single unit recordings were taken from the spinal cord, cerebellum, tectum, and telencephalon. Neuronal responses were elicited in all these regions of the central nervous system in both species of fish during brush (mechanoceptive) and pin-prod (nociceptive) stimuli."
RESPONSES TO HEAT PROBE
"In addition, in trout, a heated prod stimulus was used. Mechanoreceptive and nociceptive neuronal responses to various stimuli were elicited in all regions, and responses were detected as far as the telencephalon in both species. In goldfish, a noxious stimulus produced greater neuronal activity than a mechanoreceptive stimulus. This was not found in trout. The accurate setting of timed prods allowed the latency of the response to be calculated in all regions. From these data, conduction velocities suggested that A delta and C fibers were activated; both fiber groups previously have been shown to be involved in nociception in fish."
PAIN PATHWAY THROUGH TO FOREBRAIN
"This study has shown that there is neuronal activity in all brain areas including the telencephalon¹, suggesting a nociceptive pathway from the periphery to the higher central nervous system of fish."
¹telencephalon = cerebrum