PACAP, a member of secretin/glucagon peptide family, is a pleiotropic hormone with multiple functions.At the pituitary level, PACAP acts as a hypophysiotropic factor regulating pituitary hormone secretion.Although its stimulatory effect on growth hormone (GH) release is relatively weak in mammals, PACAP is a potent GH-releasing factor in fish and has been proposed to be the ancestral GH-releasing hormone in lower vertebrates.In grass carp, PACAP nerve fibers were located in the anterior pituitary overlapping with the distribution of somatotrophs.