Antinociception in piauçu fish induced by exposure to the conspecific alarm substance

► Piauçu fish exposed to conspecific alarm substance (CAS) reduced locomotion. ► Subcutaneous injection of formalin (FOR) enhanced locomotion (nociceptive response). ► FOR-mediated enhancement in locomotion is reduced after exposure to CAS. ► This enhancement was blocked by naloxone suggesting that opioid signaling is involved. ► Endogenous analgesic system in fish can be activated by chemical substance that signals danger.