We report the cloning and molecular characterization of a zebrafish pronociceptin gene, which is expressed in brain and intestine. This fish precursor codes for two different nociceptin peptides, one of which presents an opioid sequence in its N-terminus, being more similar to dynorphin A than its mammalian counterparts. Our results represent a new tool to investigate the function of nociceptin and its receptor in relation to pain and drug addiction.